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Old 02-01-2013, 06:19 AM   #1
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Radiant heat issues


Hi all. We just completed a master bath remodel in which we installed electric radiant heat. I wanted to install hydronic but I was talked out of it by the plumber and contractor - talk about regretting it now!

The bathroom (not including walk in shower), is 10'x12'. It is a corner room on our second floor. There is one window and one skylight in the room. The problem is, when it is cold out (as it has been here in NY), the electric radiant is running non stop and the room isn't warming up enough. It's not cold, but there is a slight chill. There are also a few "cold spots" in the floor which are making me nuts. Question is - can I install hydronic radiant between the floor joists from the room below? The joists are 2x16" I joists 12" on center. Do you think that would solve the problem or should I put a radiator in there as well? Any opinions would be greatly appreciated. Access from underneath is not a problem and my boiler is relatively close by. The bathroom, by the way, has a wood subfloor, mud job, and then 18" x 18" porcelain tiles.

Thank you!


Last edited by mazzonetv; 02-01-2013 at 06:21 AM.
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Old 02-01-2013, 06:36 AM   #2
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Radiant heat issues


I moved this to HVAC--(Heating and cooling) there are a number of good hydronic workers there.

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Old 02-01-2013, 06:42 AM   #3
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Radiant heat issues


No idea what the size of your electric is but it sounds like its too small for the room's heat loss. As long as you've made sure that the room is tight and air sealed properly, then adding a radiator to the room to for heat and using the electric just as a way to warm the floor would turn out nicely.
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Old 02-01-2013, 06:56 AM   #4
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Radiant heat issues


Ya I am agree with Canucker, you should also think about temperature of the room and using wall radiator you can easily do it. Use of wall radiators will not make more change in your design.
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Old 02-01-2013, 10:25 AM   #5
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Radiant heat issues


Thank you - and thanks for moving the thread.

I was thinking of adding a 4' section of runtal baseboard in there (I could put it on it's own zone or tie into the bedroom zone which is in the adjoining room). However, I have a couple of cold spots in the floor that I would like to address. I was wondering if I added radiant under the subfloor using those aluminum transfer plates, if that would take care of the cold spots and heat up the room enough. If the radiant isn't enough, I could do the radiant and install a runtal baseboard. The other issue is what to do with the electric radiant? I have the electric radiant running through the bathroom and into the shower (it's on a GFCI breaker according to the mfg. spec). With the hydronic radiant under and the baseboard, the sensor would probably never call for heat.

any advice?

thank you!!!
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Old 02-01-2013, 10:55 AM   #6
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Radiant heat issues


For the best efficiency, I would tie the baseboard into the bedrooms, if you can. Putting 4 ft on its own zone would be way too small for the smallest mod/con boiler. Yes, adding the underfloor heating would most likely shut the electric system down because of the floor temp. How big are the areas not heating? Were they supposed to be covered in the initial install? Its hard to give you a blanket solution without seeing what you have for a set up but one thing you could consider is, if the areas are small, you MIGHT be able to route the supply and return piping for your baseboard under those areas to warm them a bit. I have cast iron rads but i can tell where I ran the supply lines under my floors. You'd probably still notice a temp difference if the zone its on isn't calling for heat though. Insulating under the floor may help even the temps out, if you haven't done that already.
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Last edited by Canucker; 02-01-2013 at 11:27 AM. Reason: spelling
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Old 02-03-2013, 08:15 AM   #7
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Radiant heat issues


This reply is more for future users of radiant as primary heat;

Anytime you plan to use a single source of heat as the primary source, you MUST complete a heat loss calculation to know ahead of time how much heat is needed to keep the room warm. You can warm a floor that will have little benift to the room or you can heat the room at the same time by producing more btu's (or watts) psf.
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Old 02-03-2013, 02:16 PM   #8
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Radiant heat issues


Thank you all. The areas not heating are the floor under the vanity seat (so my wife's feet are cold when she is sitting and drying her hair), and around the toilet - not bad if your sitting but if our standing your feet are cold =). In front of the vanities are cold as well - if i ever run electric again ill go right around the toilet and under the vanities!

if I run hydronic radiant, I think I would do it under the entire room, and tub as well, so the tub stays warmer in the winter.

I guess my main concern is how effective and what kind of output could I expect from hydronic radiant that is run under the subfloor, given that the heat will have to radiate through the plywood subfloor, mud job, and then tile.

Thank you all

Point noted about the heat loss calculation - wish I could go back and do it all over again
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Old 02-03-2013, 05:23 PM   #9
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Radiant heat issues


If you haven't done it already insulate the floor from below, minimum I recommend is R-11 but you can't over do this. Give that a try first and see what improvements you realize. If you do opt to put hydronic heating between the joists you'll have to do this anyhow (insulate) so the effort and expense won't go to waste.

If you don't have hydronic radiant heating in the home already you probably don't have easy access to low water temperatures from your existing system. To use high temperature water (~140 - 180+) do not use a direct contact installation like the plates you mentioned.

With a high temperature supply you can suspend piping between the joist spaces then insulate below them leaving an air space for the pipe to heat.

Without knowing how the existing hydronic system is set up it's pure guessing as to how you would best control and use this type of added zone. If you extend the bedroom zone under the bathroom floor do so by extending the return piping that is cooler.

My guess is that the best system for what you're hoping to do is a hybrid zone with a buffering tank, temperature mixing and it's own thermostat. By doing this you spend more money, but you have the best control and the Mrs. would be happiest. By doing this you have maximum flexibility over how you install it. Too warm of temperatures at the base of the toilet and where someone with bare feet is sitting will only replace one problem with others.
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Old 02-03-2013, 07:22 PM   #10
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Radiant heat issues


The floor is insulated, but only with fiberglass and they are 16" joists, so lots of space to do something better. I'm wondering if it makes sense to use spray foam after the hydronic radiant is run - any thought on that??


I do have one other radiant zone in the house, so I don't see any issue with adding another. Would it make sense to run the radiant using the aluminum plates, at a lower temp, and then use a runtal radiator in the bathroom also on the same zone as the radiant heat? I guess I would do a heat loss calculation to size the radiator, but not sure what kind of output I could expect from the radiant. The runtals work off lower temps, and then I could have one thermostat for the bathroom.

I could then (at least in my mind), disconnect the sensor from the electric radiant heat and just use that thermostat on a timer (if I want) to heat up the floor and bench in the shower.

Thank you so much for the advice!!!
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Old 02-03-2013, 08:24 PM   #11
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Radiant heat issues


Don't spray foam over hydronic radiant. unless you like lots of floor noise when the plates expand inside the foam.
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Old 02-03-2013, 08:37 PM   #12
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I'm going to throw this out there. You could make it a whole lot easier on yourself and use a retro-fit electric system. Look up Calorique radiant as aretro-fit.
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Old 02-05-2013, 08:19 PM   #13
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Radiant heat issues


I have electric radiant on top of the mud job now - don't see how adding more electric under the subfloor will help.....


Any ideas from anyone on how well the hydronic radiant under the subfloor? Is there an online calculator that can help me figure out how many btus ill need to heat the room??

Thanks!!
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Old 02-05-2013, 09:48 PM   #14
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Radiant heat issues


Quote:
Originally Posted by mazzonetv View Post
Thank you all. The areas not heating are the floor under the vanity seat (so my wife's feet are cold when she is sitting and drying her hair

if I run hydronic radiant, I think I would do it under the entire room, and tub as well, so the tub stays warmer in the winter.


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I don't know what your access is, but there are small hydronic heaters which are actually "toe kick" heaters. They could easily fit under the vanity cabinet. You will obviously need the piping and electric there as well. They are invisible and just may provide the main heat for the room and the electric can be the supplemental.
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Last edited by Missouri Bound; 02-05-2013 at 09:50 PM.
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Old 02-06-2013, 03:55 PM   #15
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Radiant heat issues


Quote:
Originally Posted by mazzonetv View Post
I have electric radiant on top of the mud job now - don't see how adding more electric under the subfloor will help.....


Any ideas from anyone on how well the hydronic radiant under the subfloor? Is there an online calculator that can help me figure out how many btus ill need to heat the room??

Thanks!!
Most of the suggestions you're getting are cost effective ways to supplement what you already have. Yes, you can heat the space with staple up hydronic but you still need to insulate under it, just like the electric. Additionally, the return temp of the water required to heat the space that way, most likely will be out of the range for a mod/con's most efficient range, if that's what you have. Plus, a mod/con, if sized right, can regulate the temp of the water to match the homes heat loss, which may or may not result in your floors actually being warm most of the time. You can set the electric up to have warm floors almost all the time.
Personally, I would leave the electric you have, use the retrofit electric in the link provided by warmsmeallup to address the cold spots and if you don't mind air blowing on you, use the toe kicks that Missouri pointed out to heat the space. If you don't want air blowing around, used a baseboard like you planned.
OR, rip it all out, get a heat loss done, spend the money on some warmboard for the floor AND ceiling, and do this right. The second way will not be cheap.

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