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Baseboard Heating

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Baseboard Heating Not Heating Uniformly

The Home Wizard app calculates your ideal home care program to avoid problems with your Baseboard Heating, but sometimes trouble can still occur. Here are answers to questions about baseboard heating not heating uniformly.


Hi...we heat our bungalow with full basement with hot water heat and have a combination of cast iron rads and fin type baseboard radiators. The boiler is new however we now have a problem in getting heat in a 30 foot section of fin type rad in basement. All other rads in the house work fine. There is no air bleed valves to bleed air from in this basement rad. The first 10-12 feet of rad begin to get hot but as the boiler temperature increases (approx 140-150 degrees) the pipe grows cooler. Seems very unusual to lose heat in line when boiler temperature is increasing. Never had problem before with this extended length of baseboard previously. Our boiler did quit one evening when i had flue problem but i can't say with any certainty that this created the problem with this basement baseboard heater. Would putting in a bleed valve at the end of this baseboard heater solve the problem??? While there may be air in line how can the line begin to get hot and then lose this heat as the boiler temperature increases??? Is this not strange?? Thank you kindly for your help.

Continued . . .

Hi...I have new gas boiler with the rads in the house being a combination of cast iron and fin type baseboard. In the basement I have a long section of baseboard rad that only gets hot half way down. As the boiler temperature increases I eventually lose most of the heat i already had in that line. In other words, the baseboard rad cools off the longer I run the boiler. All other rads in house work fine and there is no where to bleed boiler in basement. Is this not a very unusual situation?? Comments or suggestions greatly appreciated Wizard....



Dear Bhrin:

Yes, what you are describing does sound very unusual.

I assume that this section of baseboard radiators are on a separate zone from the rest of the radiators in your bungalow, correct? By this I mean that it has a separate thermostat, and the piping for circulating water from through the boiler runs separate from the other piping lines that would serve each of the other zones in your bungalow. And further, I assume that your boiler is likely in your basement, right?

A couple of things that could be causing your problem.

First, yes, I'm wondering if you could have air trapped in your system, but I would think that you would have mentioned something about hearing "gurgling" or rushing water sounds in the lines.

Then what I'm wondering is if there is a problem with the circulation pump (or thermostat) for the zone that serves your basement. Then, when your boiler turns on to serve OTHER zones in your bungalow, the hot water warms up the pipe and part of the baseboard closest to the boiler in the zone that serves your basement, but because the circulation pump is not running properly, the rest of the baseboard further down the line doesn't get heated up.

What you can do to test this is turn down the thermostats on all of your other zones, and then turn up the thermostat in your basement, and then go to your boiler and see if you can hear one of the circulation pumps running on the pipes coming out of your boiler (for example, if you have three zones, i.e, three thermostats, you should see three pipes coming off the line coming out of your boiler, and each of these lines will have a circulation pump on it). If none of the circulation pumps are running, then there is either a problem with the circulation pump or with the thermostat for this zone.

And now, regarding why the pipe seems to get colder when the boiler is running, what I am thinking is that the boiler is running to serve other zones, but your basement zone is not circulating as described above. Therefore as the other zones are running, what I'm wondering is as their circulation pumps are running if they actually then draw the pressure down on the zone for the basement, and since this zone is not running that then somehow begins to pull the hot water back from this pipe and therefore makes the baseboard radiator start to feel cooler.

I'm sorta just guessing here, because it difficult to tell without being able to physically see your system.

But why don't we start by doing the test that I described above, to see if the problem is related to your circulation pump or thermostat for your downstairs zone.

And if you do decide that you need to purge / bleed the air out of the zone that serves your basement, you can find the procedure for how to do this in the Question & Answer section of our Baseboard Heating System webpage in our online Maintenance Library:

Hope this is helpful. And please let us know what you find out, and then we can try to help you further.


I am so impressed with the help you offer when its free...this kind of info is way beyond what i expected from a fellow that is as busy as you appear to be.

I tried to be concise with my question so as not to have you read endless amounts of dialogue but then i guess i forgot to provide crucial info. My apologies. There is only one thermostat and to my knowledge only one zone as the system was put in years ago by people obviously not as sharp as you. I believe it always provided good heat before and perhaps it became problematic when my boiler quit awhile ago due to a minor flue issue. The boiler is a year old and a viesmann (circulator brand new as well) so i think the problem must lie in the lines. This particular baseboard is about 35 feet long and has a 90 degree turn but i think i have it reasonably level. The copper line seems to be an inch or perhaps inch and a quarter so it should give off lots of heat. It gets nice and hot for about 10 feet but once the boiler temp reaches around 150 degrees it starts to cool down. Would putting a bleeder valve at the end of the line do any good?? There are no shut off valves anywhere in basement and essentially what i have is a big copper line running the perimeter of the basement. I dont hear a lot of gurling in line but perhaps there is some air in the end. The pressure is about 20 psi and if i did as you suggest to clear out air i would only be able to raise the pressure about 8 lbs or so and would this really make any difference??

Again I am so impressed that you would take the time to help all us dummies out. Thank you very much.



Glad to try to help you out, and yes, we have some GREAT sponsors who allow us to make this free service available to you ( ) !

I'll need to ask a few more questions:

When you say you have only one zone, you mean for the entire bungalow, not just for the basement, right? And there is only one thermostat for the entire bungalow, and near the boiler you only see one circulation pump for one line coming out of the boiler, right?

Could you please tell me more about how the pipe in your basement gets hot, but then starts to cool down when the boiler reaches 150 degrees. Can you describe for me exactly what is happening. Does the pipe in your basement start to get warm when the boiler comes on, and then when the boiler gets up to it maximum temperature does the boiler turn off and THEN the temperature begins to drop in the line down in your basement?

Is the end of the pipe in your basement that gets hot closer to or further away from where your boiler is located (I'm trying to figure out which way the water is flowing through this pipe)?

Do you know if this section of piping in your basement was added after your bungalow was originally constructed? In other words, was your system designed for standard radiators, and then later this section of baseboard heating in the basement was added?

Do your radiators upstairs all have bleeders?

Regarding your question about adding a bleeder to your baseboard line in your basement, I don't think this would help. If water is flowing through this line, it would move the air with it, and then this air would get trapped in the radiators on your upper floors, where you could bleed the air off. However, not knowing what style radiators that you had upstairs is why I was wondering if it could make sense to purge/bleed you system using the drain valve near your boiler. And regarding your question about purging/bleeding the lines, you actually don't have to raise the pressure to do this, it just helps the process go a little quicker. While purging you would want to keep the pressure from dropping.

But again, it does not sound like you have a trapped air problem. However, if you can let me know about the above questions, we can take it one step at a time, to confirm this, and figure out what is causing your problem.



Hi again...more than happy to answer your questions & apologize for not giving u a better handle on this. The house has only thermostat and only one pump with one line going out. The upstairs has a combination of cast iron rads and fin type rads. The basement has only one cast iron rad and about 45 feet of fin type. All the rads upstairs have been bled and work fine while the cast iron rad downstairs and a seperate 10 ft section of fin work well in basement. It is this one 35 foot section of fin where the problem lies. The end closest to the boiler warms up nicely when boiler starts and gets quite hot for about 10 feet. After that it is only warm and usually will get warm right to the end of the line before it heads up to the floor joists. As the boiler continues to run and reaches about 150 the line starts to grow colder even as the boiler runs. When the boiler temp reaches 160 or so and is still running the pipe is quite cold. The end nearest the boiler is still warm but a point 10 feet away is actually cold. I am afraid i cant tell you when things were added but there was an addition (family room) where 2 cast irons rads reside afer original house built. As i mentioned the basement area has always been warm and perhaps the problem surfaced after our boiler went out a couple of times a month ago. I had a young fellow out to look at it but he is relatively inexperienced and just suggested a bleed at the end of the line in basement. His theory, was that the line has air in it towards the end and is not moving. He had no answer for why the line gets colder as boiler gets hotter and i dont blame him as that is puzzler. I live in Canada where it gets real cold(-40) and there is shortage of people who understand hot water heat. Hope this sheds more light on subject and again many thanks. Incidentally, there is a bleed valve in the floor joists above the end of the line and when bled we just get water.



This is helpful, and I think I'm getting the picture here.

The end of the pipe that gets hot is the end that is closest to the boiler, right?

From what you can tell from the piping you see going into and out of the boiler, can you confirm that the line coming back from your basement is at the end of your heating system? In other words, does hot water come out of your boiler, and then have to go through all of the other radiators in your bungalow before it goes down to the basement and then back to the boiler?

If so, I'm wondering if what is happening here is two things:

1) the boiler was not originally designed for as many radiators and baseboard heating pipes as have been added over time. As a result, by the time the water circulates down to the basement, the water is cold since it has already given up all of its heat in the other radiators.

2) the reason the end of the pipe in the basement gets hot is because it is connected to the boiler, and it conducts heat along the pipe. But then as the boiler runs longer, and the water circulates through the pipe in the opposite direction, the cold water from #1 above starts to cool this pipe down.

As I mentioned before, its difficult to diagnose without physically seeing your system operating. But does this sound like what could be happening?


Hi...i just noticed that the cast iron rad upstairs directly above where the fin rad starts in the basement is much hotter on top of the rad than the bottom of the rad. I did bleed it and got a tiny amount of air but discrepancy in temp between top and bottom remained. Could this be the problem??



I'm wondering if what you are seeing with this radiator is as a result of sludge build-up in it. Here's a drawing showing what I'm referring to:

And this is usually indicated by a radiator that is hotter on the top than it is on the bottom (because the sludge acts as an insulator).

Do you think this is what you are seeing?


I have a HW base board return heating system.We just bought the house last year.This winter has been very cold.The furnace was replaced last year.We cannot get enough heat.The room temp. stays around 60 or lower.I was told there is not enough footage of base board installed.My main concern is the new furnace is being over worked.I am going to add (additional attic insulation).If I dont add more base board in the house and just tough it out thru the winter.
1- Are my fuel costs increased because of the lack of base board.
2-Is the furnace being overworked,therefor shortening its normal life and efficiency.
Thank You


Dear Dennis:

There could be a number of issues that you could be facing, so let me go through each of them.

It could be possible that when your furnace was replaced last year that it was replaced with a unit that is too small for your baseboard heating system. Hopefully this wasn't something that the previous owner did on purpose when they knew that they were planning to sell the house. On the other hand, the problem could be that the furnace is adequately sized, but it is not getting adequate fuel supply. For example, if you use oil, then the fuel nozzle could be too small. Or your gas regulator could be set too low.

Regarding adding footage of additional baseboard radiator versus additional insulation, yes, it would be much better to add insulation and save energy (heat) , rather than just putting more heat into the rooms. In addition to more roof insulation, you might want to consider replacing your windows with higher efficiency rated windows, weatherstipping your doors, blocking electrical switches on outside walls, etc.

With respect to your question about increased fuel costs due to the lack of sufficient baseboard length, it actually will increase your electric bill because your water circulation pump will need to operate for longer periods of time (and if you are only getting up to 60 degrees F in your home, then your system is probably running constantly). But your fuel costs will probably be lower because you are not getting enough heat (energy) into the rooms.

But this raises the question as to whether your furnace is too small, or if your baseboard lengths are too short. One way to check this is to carefully check the temperature of the return water that is circulating back to your furnace (be careful grabbing any pipes around your furnace, as they could be very hot). If the water return pipe at your furnace is relatively cool, then the problem is not that baseboards are too short, but more likely that the furnace is not putting enough heat into the water supply (this is why the hot water "runs out of gas" by the time it runs through the system . . . assuming that you are not losing excessive heat through leaky windows, doors, electrical switch plates, poor insulation, etc.). But if the return water going back to your furnace is relative warm, then the furnace size is probably fine, but there isn't enough length of baseboard radiators to remove heat before it goes back to the furnace.

And finally, regarding your question about your furnace being over-worked, yes it's not good for its service life if it is running all the time (and still not heating up your home). However, it is not as bad as the reverse problem of your furnace cycling too often because it is over-sized for your system.

And regarding the efficiency, it's actually more efficient to operating in steady state than cycling, but the problem is that you are not getting enough heat into your home.

Hope this is helpful.


I have a baseboard hot water system. There are 3 zones and only the basement zone gets really hot. On The first floor and the second floor you hardly can feel the heat. Air is out of the baseboards and clean. Also, How do i drain the expansion tank?


Dear Victor:

If one of your heating zones is getting hot, but the other two are not, here are some things to check:

1) You said that air is out of the baseboards, but you might want to double check that you have properly purged all of the air out of each of your two upstair heating zones. If you need the procedure for doing this, you can find it in the "Question & Answer" section of our Baseboard Heating System webpage of our online Maintenance Library:

2) Check to be sure that the thermostat controlling each of these zones is working properly.

3) Check to see that the valve controlling the flow to each of these zones is not stuck or blocked.

4) Check that the circulation pump for each of these zones is working properly.

Regarding your question of how to drain the expansion tank, I will answer this for you separately as part of your second posting to Ask-the-Wizard.

However, are you asking about draining your expansion tank because of the problem you are having with your second floor zones not heating up? Or is it because you are seeing the symptoms of the need to drain your expansion tank:

o The pressure relief valve on your boiler is spurting out water.

o The pressure gauge on your system is reading too high (above 20 psi).

o Your expansion tank feels hot to the touch, both at the top and at the bottom.

Hope this is helpful.


What is the purpose of my heating system’s expansion tank?


Dear Victor:

The purpose of an expansion tank in a baseboard hot water heating system is that acts as a surge tank for pressure variations in your system, and it prevents water in your system from boiling and exceeding the optimum system pressure of 12 psi. To operate properly, your expansion tank must be charged with air. If your expansion tank is either has too much, or too little, air in it, then it cannot do its job properly.

If your system is an older installation, then your expansion tank is likely found in your attic, otherwise in newer heating systems the expansion tank is typically either attached to the boiler piping or hung from the basement ceiling near the boiler.

As I mentioned in my earlier email to you in response to your first posting to Ask-the-Wizard, the symptoms that you expansion tank need to be drained include:

o The pressure relief valve on your boiler is spurting out water.

o The pressure gauge on your system is reading too high (above 20 psi).

o Your expansion tank feels hot to the touch, both at the top
and at the bottom.

If this is the case, then here is the procedure for draining your expansion:

1) Turn off your boiler, close your heating system water supply valve, and let your expansion tank and heating system cool down.

2) Attach a hose to the purge valve on your expansion tank and drain out the water (usually about 3 gallons).

3) Be sure the purge valve has closed, and then open up your system's water supply valves and let the system fill back up.

4) Turn you boiler back on, and let your system recharge.

5) After you system runs for several hours, check your expansion tank again to ensure that it is no longer hot at both the bottom and top of the tank.

Hope this is helpful.


if i add a 3rd zone to my house do i need to adjust anything ? (water temp or psi or the expansion tank)
The reason to my ? is that the new zone works much better that the other two.
I have a water heat system and they work with 3 independent pumps.


Dear Victor:

If you add an additional heating zone to your baseboard heating system, then there are two things that you need to do. And not doing one or both of these can result in the performance of the new zone being very different than your existing zones:

1) The linear feet of baseboards that you install in the rooms served by the new zone needs to be appropriately matched to the heating requirements of those rooms. And the baseboards need to be installed in the appropriate locations, for example, on exterior walls near cold windows and doors.

2) Balancing valves need to be installed, to keep the hot water in your system from traveling the path of least resistance, and not providing enough heat to the baseboards that need it. As the name suggests, these balancing valves can be closed down on the shorter or "easier" loops, forcing more water to flow through the longer or loops with more elbows and bends, which are harder for water to flow through. By installing and properly adjusting the balancing valves, you can achieve more uniform heating throughout all of rooms served by all of your zones.

Hope this is helpful.


Hi, I've been reading your posts about heating system issues. I have a rather new 2 story Cape Cod style house and have a minor heating issue. I have 2 zones. The first floor heats very slowly. Second floor heats quickly. I suspect the number of footage of baseboard is not enough to handle the larger first floor. I have removed the front panel of one of the baseboards and placed a small fan next to it and the house heats more quickly. I assume this confirms my suspicions about not enough baseboard for the size of the floor. What are my options? I assume that I could hire a plumber to put in more baseboards. I've also heard of small units that can be added under the kitchen sink that "blow" warm air into the room. Are these my only options? Can anything be done to the existing baseboards without hiring a plumber. This is only a problem when the house gets cool and needs to heat up as with a setback thermostat.


Dear Rick:

If you are not seeing sufficient heating capacity coming from your first floor baseboard heating zone, here are some thoughts on potential options:

1) You are correct, you can install a blower unit, which blows air across a section the baseboard pipe.

2) And yes, you can install additional linear feet of baseboard, assuming that you have the room to do it.

3) However the problem could be an indication that you need to bleed your the air out of the zone which serves your first floor.

4) The problem could also be an indication that you have a faulty circulator pump that is not circulating enough hot water through your first floor zone.

5) You have something blocking the first floor baseboards. A common example of this is loose or poorly installed carpet.

6) The damper on the top of the baseboard may have been closed, and this will reduce the heat capacity of the baseboards.

7) A heavy build-up of dirt, dust, animal fur or household items that have fallen on top of the baseboard fins, which can reduce the efficiency of a baseboard radiator. (Although since you said you had a rather new house, this option may not be likely, unless you have been sanding floors, or that you have heavily shedding dogs).

Hope this is helpul.


We have radiant baseboard heating on 2 floors in 5 zones. a) when the thermostat is turned on in 1 zone it just makes a clicking sound; we don't use it. Is this a faulty control unit or air in the lines or....? b) our upstairs bedrooms zone seems to produce heat even when not turned on. If any other zone in the house is turned on it seems to impact the bedrooms. If turned completely off, the bedrooms are fine until another zone is turned on again. It's not just rising heat; the baseboard heating units seem to generate heat even though only other zones are turned on. Is this a faulty control unit(s)? My understanding is that all zones are "closed" so wouldn't think one would impact another. c) how do you know if you have air in the lines? d) can home maintenance be performed to maintain these units or are professionals required?


Dear Daryl:

Let me address each of your questions one at a time for you:

a) When you say that your thermostat for Zone 1 "just makes a clicking sound and you don't use it", could you tell me a little bit more about this? Is it the thermostat that makes the clicking sound? Or is it the baseboard pipes that make the clicking sound as the pipes are heating up?

b) Regarding the problem you are having with the upstairs bedroom zone heating up when other zones are turned on, when you look at your furnace/boiler, do you see 5 control valves with on 5 separate pipes coming out of your boiler (for example, like the 3 red valves in this photograph: ) ?

c) Symptoms of air in your baseboard heating pipes include: a gurgling or whoosing noise through your pipes when the heat is on; loss of heating efficiency; or banging noise when heat comes on. If you need to purge the air out of your baseboard heating system, you can find instructions on how to do this here on the Home-Wizard website.

d) Home maintenance for your baseboard heating system includes vacuuming and cleaning around the baseboard louvers, and opening and closing the covers depending on the season. These are straightforward to do. Purging air from your system is a procedure that many homeowners are comfortable doing themselves (especially using the procedures we provide here at, however, you need to be very careful of scalding water and not to overpressure your boiler. If you have any concerns about doing this yourself, then yes, its better to leave it to a professional. A separate topic is the important routine maintenance for our furnace/boiler. This is definitely something that most homeowners have done by a trained professional.

If you could let me know about the questions above, I can better help you diagnose your problems.



Thanks for your response.

a) It seems to be the actual control unit (by the boiler) that is clicking.
There is 1 controller for each zone. It's not the thermostat or the pipes.

b) Yes 5 control valves on 5 separate pipes.

c) Thanks - don't think we have air in the pipes

d) Thanks

Happy New Year


Dear Daryl:

Thanks for your clarifications.

From what you've described, it sounds like it is not air in the lines, nor problems with your thermostats.

However, it sounds like something may not be right with your control unit. If you have the proper electrical testing tools (and are comfortable working around electricity), then you can test each zone valve at your boiler to see which one (or more than one) comes on when your turn up and down each of the 5 thermostats for each of your heating zones. Otherwise, this is something that you would want a trained professional to do for you.

One other thought, and this may be a bit of a longshot, is that if what you are seeing is not a new problem, I'm wondering if your heating pipes run together beside each other in the floor joists or wall, and when one zone turns on that it heats up the pipe that serves another zone? But this would not show up as a new problem, but rather this would start happening from the beginning when the system was installed.

Which is why it sounds like a problem has developed with your control unit.

If you are interested, here is a webpage that describes how the control system for a baseboard heating system works:

Hope this is helpful.


I have a two zone gas baseboard heating system. In seems that no heat is going to one room only in the entire house under zone 2. Are there controls inside the baseboard unit or a valve that allows water into that room's unit pipes, etc? Please advise? Since it is the room above my garage, it is like a freezer in there! Thanks in advance


Dear JMJ:

If you have one zone of your heating system that is not getting hot, then the first thing that I would recommend is that if you haven't already, you should try bleeding the air out of this zone. The procedure for how to purge the air out of a heating zone can be found in the "Question & Answer" section of the Baseboard Heating System webpage of our online Maintenance Library:

If you have already bled this heating zone and you are still not getting heat in these baseboards, then the other possible problems include:

1) the thermostat in the room controlling this zone is not working properly.

2) the valve controlling the flow to this zone is stuck or blocked.

3) the circulation pump for this zone is not working properly.

Hope this is helpful.


I recently bought a co-op apartment with baseboard hot water radiators. One of the radiators puts out very little heat, mostly from the bottom of the pipe, so I'm assuming it needs to be bled. My questions:

1. Since my apartment is on the 2nd floor of a 4 story building, I don't have access to the main boiler for turning off anything there. Can I just go ahead and bleed the radiator?

2. The radiator has a valve similar to the one I have on the main water meter in my home, and like any outside water valve you might use with a garden hose, etc. Is this what I use to bleed the radiator? I don't see any other valves, only on/off levers on either end of the radiator.

3. If this is the valve to use and do I just turn it on and have a pail or receptacle to catch the water? At what point do I turn it off?

Thanks for your help.


Dear Bob:

Regarding bleeding your radiators, it depends on what type of radiators and heating system that you have. Here a couple of videos which show how to bleed radiators. From your description of the radiator putting out heat mostly from the bottom, it sounded like you have a wall-type radiator system, so here are videos for wall style hot water radiators:

And if you have a baseboard heating system (single pipe with fins around it), here is a Home-Wizard video which describes how a baseboard heating system works, and if you skip ahead to around the 6-minute point in the video, it will describe how to bleed air out of the system:

Hope this is helpful.


We recently moved into a duplex (4th & 5th floor) in a relatively new 5 floor apartment building and have begun using our unit’s heat for the first time this winter. Each unit has its own gas fired, hot water, baseboard heating system with one zone. We have noticed that the 5th floor radiators do not put out the same level of heat as the 4th floor radiators, resulting in the 5th floor being much colder than the 4th floor. Someone mentioned that the boiler’s pressure could be adjusted to increase the heat output to the 5th floor. Is this possible? Or, is there something else that can be done to increase the heat output on our unit’s 5th floor?


Dear John:

Here are a couple of reasons why your higher floor may not be getting as much heat as your lower floor:

1) You may need to purge air out of the heating system. Air trapped in the pipes can cause your heating system to operate less efficiently, and as a result, not have the heating capacity to heat both the 4th and 5th floors. You should talk with your apartment manager about the procedure for purging/bleeding the air out of your particular heating system. It may be something you can do in your apartment, or it may be something that they will need to do down near the boiler.

2) It may be a balancing issue. For example, if the hot water circulates first through the 4th floor before it circulates through the 5th floor, then it may be losing too much heat on the 4th floor, and not leaving enough for the 5th floor. If your system will allow it, you might be able to close the louvers down a bit on the baseboards on the 4th floor, and leave the 5th floor louvers wide open. This way your system will run longer to heat up the 4th floor, but in the process could allow the 5th floor to heat up.

3) It may be a thermostat location problem. This might be a bit of a long-shot, but you said you only had one zone, so if the thermostat for the zone was located on the 4th floor, then when the room with the thermostat in it on 4th floor is warm enough, it would shut off the heat, even though the rooms on the 5th floor might not have gotten up to temperature.

4) As far as the water temperature and pressure of your boiler, yes these are worth checking to see if they are operating in the proper range. As well as checking whether the boiler has sediment buildup. These can all keep your heating system from operating a full efficiency.

Hope this is helpful.


Thanks so much! Since air rises, does it usually get trapped at the top of the system? (5th floor) Or does it circulate trough the system?

Thanks again



If it is a closed baseboard heating system, the trapped air is circulated through the system with the water. But if it is a radiator style heating system, the air can get trapped in pockets at the top of the radiators (here is a drawing showing a radiator, and you can see how air can get trapped in the top: )

In a baseboard heating system, the air that is trapped in your system gets pushed around by the water and ends up circulating around through the pipes. But if you had radiators, the air could get trapped at the tops of them, and the water could be circulating below this trapped pocket of air. However in a baseboard heating system, the small diameter pipes don't leave room for pockets to form, but rather the trapped air flows around with the water. Which is why you can hear a "gurgling" sound or water rushing sound when you have air trapped in a baseboard type heating system.

Hope this helps.


I have a puzzling problem with baseboard heating in my house. It is a two floor house with 3 zones.
2 zones on the first floor and 1 on the second floor. When I turn on the thermostat for zone that heats main portion of the 1st floor (zone1), the radiators of the upstairs zone (zone2) get hot.
When I feel the pipes, the 1st floor zone1 supply line is hot. The 2nd floor zone2 supply line is cold. The thermostat of the 2nd floor zone is turned off. The house has a return line that runs the length of the house in the basement. There is a 3 way T connector on the opposite end of the house, which has the 2 returns from the zone1, and one return from zone2. That return line from 2nd floor is hot.
I had personally inspected the plumbing with my oil company repair man. All the splits and pipes are accounted for, and the situation does not makes sense to him. He says that there is noway the zone2 can get hot from the return line.
Each zone has an electric motor, as well as the return pipe. They added backflow check valves to each zone, next to the motors, but it did not help. The second zone (zone3), serving another part of first floor stays cold as expected.
Is there a reasonable explanation for whats going on?


Dear Max:

If I understand you problem correctly, the baseboard heating zone on your second floor is getting hot, even though the thermostat for the second floor is turned off, right?

A couple of thoughts:

1) Have you checked to ensure that your thermostat on the second floor is operating properly? If it is defective or not wired properly, then it could be calling for heat, even when it is in the "off" position.

2) Does your second floor baseboard zone only get hot when you turn on the first floor zone 1? In other words, if you have both zones 1 and 3 turned off, does zone 2 upstairs ever get hot on its own? Also, when you say that the "2nd floor zone 2 line is cold", where are you testing the line? Is it down near your furnace, or up closer to the second floor? If the 2nd floor zone only gets hot when you are running zone 1, and the pipe is cold near the furnace, then the next thing to check is whether the supply pipes for zones 1 and 2 are running side-by-side for a long way inside the same floor joists, such that it could be heating the zone 3 piping. I've seen this happen where a heating supply pipe was run along side a cold water pipe, and when the cold water faucet was turned on, the water would come out scalding hot. But in your case, the question would be whether when you turn on zone 1 (with zone 3 upstairs turned off), does the circulation pump for zone 3 also turn on (which would circulate the water heated up by running next to the zone 1 piping)?

If you could give me a little more information for the questions above, I can try to better diagnose your system's problems.



We live in a two story apartment with hot water baseboard heating. First floor gets plenty of heat.
Second floor bedrooms get very low heat despite
out turning the thermostat on the second floor
up high.

Could it be the thermostat? air in the pipes?
This has been going on for a week. Help Im freezing...


Dear Ryan:

If one of the two zones of your hot water baseboard heating system is not warming up, then here are some potential causes:

1) The zone needs to be bled of air. You can find a procedure for this in the question and answer section of the "Baseboard Heating System" webpage of our online Maintenance Library:

2) Your circulation pump for this zone has gone bad and is not circulating enough hot water.

3) The check valve in this zone is partially stuck, and is reducing the flow rate of hot water (you might be lucky enough to solve this problem with some raps on the valve with a piece of wood, NOT a hammer).

4) The thermostat for this zone has gone bad.

Hope this is helpful.


I have a 1-zone hydronic baseboard system which heats a basement, 1st floor, 2nd floor and a small room in the attic. There are 3 returns, each with a bleeder/return valve. The thermostat is on the 1st floor. The 2nd floor and attic aren't heating nearly as warm as the 1st floor. There are bleeders in 1 of the bedrooms and the attic baseboard, which I've bled all the air out. I've also tried bleeding at the return valves and no air gurgled out after a thorough session. The return pipe for the upper floors doesn't get nearly as hot as the other two. Two questions:

1. I recently replaced the circulator pump with a lower horsepower Taco model. Can this be a reason why the upper floors aren't heating as effectively?

2. Can I get more heat upstairs simply by partially closing the return valves that come back from the 1st floor & basement?


Dear Frustrated:

If you have already done a thorough job of bleeding your system, and if the piping of your system is such that water from your boiler goes first to the radiators on your first floor, then yes, your problem could be the lower horsepower of the Taco circulation pump that you installed. And yes, you can try partially closing the return valves that come back from the first floor and basement.

The risk is that your circulator pump may fail sooner, since you will need to run this pump longer to heat your home (circulate the hot water), than would a higher horsepower pump that your system was designed for.

Hope this is helpful.


I have gas baseboard heating. I have one zone in my home. Within the past two days, I've noticed that my daughter's room radiator is cold when the other radiators are warm. I don't understand. It seems illogical to me. The radiators in the rooms on either side of her bedroom are working. Can you help me?


Dear Tom:

Since you only have one heating zone, and there is one section of baseboard radiator that is cold and the rest are hot, it sounds like the problem is that you have a section of baseboard radiator that is "air-blocked."

Here is a webpage that describes what "air-blocked" is, and how to fix the problem:

Hope this is helpful.


This is a follow up from my 12/30/09 response from you. I have one zone baseboard heating with one radiator not heating up. It seems to be one in the middle of the circulation. I turned up the thermostat, let it heat up, checked the other radiators (they were all hot)the one was still cold. I have unscrewed my single air bleed valve (like a bicycle tire valve). Nothing came out. I depressed the valve stem & I got a shot of air, then water. I closed it. Then loosened it. The radiator (I waited about 10 minutes) is still cold. What do I do next? Is there anything I can do?


Dear Tom:

When you turn up the thermostat and let the other radiators heat up, and then purge the air out of the bleeder valve . . . when the water starts to come out of the bleeder valve is the water hot, warm or cold?


The water that comes out of the bleeder valve when I push the valve down is very hot.

What does that mean?


Dear Tom:

You said that you have one heating zone, and the section of baseboard radiator that does not heat up is located in between sections of baseboard radiators that are working fine.

Is the piping for your heating system a series loop system, where the main supply goes from boiler into one radiator and then to the next, and so on? Or do your radiators have a diverter valve for each section, which diverts the flow of water into that section of radiator?

If it's the latter, then I'm wondering if you have a problem with the diverter valve for the section of baseboard radiator that is not heating up. If this diverter valve is not opening up enough (or is partially plugged), this could explain why there is hot water coming out of the bleeder valve, but not enough flow to heat up the section of radiator.

Hope this is helpful.


I have an old 3 story house with baseboard steam heat. There is one baseboard that runs the entire length of the wall in the 3rd story bedroom. The first 1/3 of the baseboard heats up, but the rest of the baseboard is ice cold. I have opened the air valve and air does hiss out. But the baseboard does not heat up even after I close the valve. If I open the valve 30 minutes later, I get the air hissing again. What could be wrong?



Dear Michelle:

Steam radiators have a valve that allows steam to flow through at a controlled rate so that the radiator can heat up. If this valve is clogged with mineral deposits or stuck shut, it restricts the flow of steam to the radiator, so it doesn't heat up properly. It is sometimes possible to unclogged these valves, but usually it's better just replacing them.

Another possible problem is that the pipe leading to the radiator is not properly sloping downward towards the boiler. If this has occurred (due to your house settling, the pipe not installed properly, etc.), then the condensation within the radiator that would normally flow back to the boiler is instead pooling in the pipe. This can block the movement of steam to the radiator.

Hope this is helpful.

QUESTION FROM deanna Wilson

My baseboard heating system is only working in one of my upstairs bedrooms. What can I do to fix it?


Dear Deanna:

We would be glad to try to help you, but we will need some more background on your heating system. For example, what type of heating system do you have? Is it forced air or hot water radiators? How many heating zones do you have? Are the upstairs bedrooms in a separate zone from the rest of the house?


have one of my zones passing hot water when zone is not calling for controller shows off .three other zones fine.i also have a outside wood boiler connected to existing propane fired boiler.


Dear Dave:

Do I understand correctly that your problem is that all of a sudden one of the zones in your baseboard heating system is coming on, even though the thermostat for this zone is in the off position?

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Baseboard Heating