Can I replace a radiator with under floor radiant heat in my bathroom (Home HVAC)

Can I replace a radiator with under floor radiant heat in my bathroom (Home HVAC)

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Question Details Asked on 11/21/2013

2 Answers

In a single word answer, Yes. There are a few different companies that make the electric mats made for under the floor installed systems and they do work well if designed properly. The only hesitation I would have is the cost of running them depending on your electric rates. They do help with having the floor warm and when your feet hit the tile you will feel more comfortable. If you have hot water baseboard heat you might think about a toe kick heater under your vanity or kitchen cabinets in addition too the radiant heat under the floor. The lag time on the radiant systems makes it hard to lower the temp and then raise it durring times the room is used. One system I have used does have a timer that can be set to periods of use and they will custom make mats to any shape to match the room. I can not think of the brand at this moment but I am sure most have the same options. The nice thing about the custom mat is it takes the goof factor out durring installation since it is pre engineered and not up to the installer as to how much element you need. As I said before I would add the toe kick heater as a way to pick up the heat quickly, they hide under the cabinet so you do not see them but lend themselves well to timed setbacks. I have my heat set to drop when I leave and the floors do get cold but with my electric rates I would not like the bill if that was the only source of heat.


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Here is the counter argument — in a word, don’t. While it is certainly possible and not very expensive to do this while the floor is opened up to install the floor heating elements, if it gets to -20F outside in the winter like you say, radiant floor heating is NOT going to make your bathroom or kitchen comfortable unless kept on basically all the time, both because of the slow heating response time and also because while it heats the floor, it has to be on for a tremendous amount of time to heat the air in the room also.

In floor heating is also much energy efficient at the location being heated, because a lot of the heat goes down into the subfloor rather than all into the area desired to be heated. In the long run most of this «lost» heat will end up in the house so it does contribute to total house heating, albeit at the generally much more expensive electric energy rates rather than gas rates.

Not having an active air heating system the bathroom will be cold, so the walls will be colder in the winter and will at least condense moisture on the inside just like windows do (promoting mold and rot) though not likely as visibly, and lacking the baseboard heating system in the bathroom you will run the additional risk that any moisture that penetrates the walls from the bathroom or kitchen (and you would be surprised how much penetrates the outer wall from kitchens and bathrooms) will condenseor freeze within the walls rather than diffusing to the outside of the wall, which not only reduces the insulating value of the wall thus promoting even more icing or frosting in the walls, but also makes for interior wall mold when the frost thaws.

This process probably takes a bit more explanation — water vapor diffuses from warmer surfaces toward colder, from higher air pressure to lower (and house generally are higher pressure than outside), and from higher humidity areas or moister surfaces to dryer ones. However, it condenses at the point where the temperature drops enough to cause condensation — basically it forms fog in the wall. For a normal «warm» inside wall the vapor that diffuses into the drywall and through the base of the wall migrates toward the outer surface of the wall. At normal winter temperatures, it will generally either migrate through the outer sheathing and siding and diffuse into the dry outside air, or in colder conditions may frost up on the inside of the siding or sheathing. Minor frosting on the siding and sheathing surface like this normally does not cause rot, as the sheathing and siding are usually permeable enough to vapor that it diffuses rapidly as it thaws, so you do not get noticeable mold growth in the walls. However, if the inside wall surface is colder than normal, the «freezing front» migrates inward into the wall insulation so the moisture freezes in the insulation zone, and when it thaws saturates the insulation and causes mold there and in the adjacent studs and sheathing, and if there is constant water, rot. Therefore, having a colder inside wall surface (due to lack of an individual room heat source) can cause you very serious problems down the road. For that reason (and for comfort factors and to prevent pipe freezing), most building codes in the US require that every room in the house have a heater (forced air duct opening or baseboard heater element) per so many lineal feet of outside wall surface.

Another factor in favor of keeping the bathroom baseboard heater elements — generally, because of the small room size, bathrooms tend to run warmer than the rest of the house even with the smallest baseboard elements installed. This makes the bathroom more comfortable for use, especially when your body surface is wet and evaporating, but also through convection from the heater and its direct radiant and conductive heating, circulates the air and evaporates the moisture from bathing or showering faster, reducing the occurrence of mold.

Bottom line — if you have cold feet go ahead and put in floor heating if you want (though I do not personally recommned it, being a high maintenance and short life solution all too often), or much cheaper and lower maintenance get washable bathroom throw rugs, but leave in the baseboard element also.

Ditto to kitchen — I have seen cases where people did this becasuse they thought the basebaord elements were unsightly, and ended up screaming for help when they got mold in and under their cabinets because frost was actually condensing inside the cabinet back walls and underneath them from the moisture in the kitchen. Not something I recommend, but as ContractorDon said it is possible to put baseboard heating under the cabinets with toekick vents, though it takes much more element length to get the same heating effect, as more of the heat is going into the walls and floor and less to the air because you essentially remove most of the radiant and convective heating components (which are the main ways these heaters work) by confining it under the cabinets, so you end up with just a warm air source that slowly flows out from under the cabinets. If you go that route, be sure to have the cabinet installer and plumber coordinate their work, so the elements and their plumbing at both ends of the elements are fully assessible from inside the cabinets via removeable panels — because you don’t want to have to tear out cabinets if you get a leaking baseboard element. Also, mounting them there puts them out of sight and out of mind, sp they tend not to get cleaned and therefore lose a lot of their effectiveness due to dust buildup, and a minor leak can cause major rot before it becomes visible, unlike fully visible units.

One other factor — do not forget water pipes in the outside walls, as the baseboard elements or piping are commonly configured to keep those areas warm — if you remove the elements, you might freeze pipes in the outer walls o the coldest days.

Answered 9 months ago by LCD

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