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Community and Q&A

Supplemental heat for a bathroom

artisanfarms | Posted in Mechanicals on

I’m doing a deep energy retrofit of a 1600 sqft 1980’s vintage ranch house in Zone 5 (central NY, near Rochester).  I’m planning to use a ducted mini split for the primary heating and cooling. I would like to supplement this in the bathrooms.  I’m thinking either electric radiant for the tile floors or IR in the ceiling.  

I’m curious regarding suppliers for both and if there are significant benefits or negatives for either approach beyond the faster response of the ceiling mounted IR.  

Real world experiences with either and recommendations for vendors are appreciated. 

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  1. user-723121 | | #1

    I have used an in wall electric heater for a new bath in a lower level for supplemental heat. 240 volt with a push button timer, lots of heat when you want it right by the shower near the floor. Radiant floor or ceiling is too slow in my opinion and can burn out in time, I have had floor heat go out.

  2. Expert Member
    Akos | | #2

    One thing to keep in mind is that cold bathrooms are moldy bathrooms.

    Whatever heat source you put in there, it should be able to keep the bathroom at or above house temperature.

    I don't like cold floors, so I would recommend heated floors. Electric is pretty cheap to put in if you are re-tiling or if you have access to the subfloor from bellow.

    If you have a gas water heater, you can do a pretty cheap DIY hydronic heated floor by serpentining the hot water recirc line bellow the floor. In the winter time you can run the recirc pump continuously or on a thermostat and in the summer as needed to reduce wait time and to keep the water in the pipes from stagnating.

  3. Expert Member
    BILL WICHERS | | #3

    +1 for heated floors. Try to keep your shower or bath tub situated on only interior walls too, which will keep it warmer and make it more comfy to use in the winter.

    The exhaust fans with heaters in them are also nice but only for occasional use. If you go with in-floor heat, a controller that can turn it on automatically at certain times of day (like a little before you get up in the morning) can be really nice.


  4. onslow | | #4


    I installed a wire style floor heating system some years back to test the feel overall as well as how wire spacing affected things. Mine failed after about 6 months, but due to sensor failure not the heating wire. Fortunately, thanks to GBA postings of the time, I knew to put multiple sensors in the floor. I moved to the second of the three sensors I put in, only to have the wall unit go bad. I won't name the company as it is now almost 10 yrs after. Check reviews of any systems you consider. That unit and the wire/sensors lasted til we sold.

    As for the wire performance, that proved to be illuminating. I set the spacing manually to 1 1/2" and 3" to see if I could stretch the area covered like a good Scot Yankee. I even did a small area at 4" to test an upper limit. The 1 1/2 spacing was fairly even under foot especially if we set the temp at 80F. The 3" spacing was clearly banded to the point where tracing the wire was easy. 4" more so. The basic 5/16 porcelain tile did not distribute the heat much laterally. Maybe thicker tile would, but the conductive nature of tile suggests it will tend to show a narrow gradation. The newer flat resistive heat film types might be much more even. Big question is how sensitive the material is to being embedded, tile tools are not feathers and brushes.

    This test set up may sound quite mad, but our location doomed the house to demolition if we ever sold. A long overdue floor upgrade provided a way to demonstrate to my spouse how under floor heat would work and feel prior to making final decisions when we got to build new.

    Getting the floor to hold a perceptibly warm level was tricky. Setting the thermostat to 80 would keep it on long enough to bring the 1 1/2" parts up to a measured 86F, the 3" to 78F if I remember how I compensated for the banding. During the winter the kids loved it, sleeping on the floor like kittens. Made the kitchen too warm despite 30's levels of insulation.

    For a small bathroom you will probably enjoy warm feet in 10-15 minutes from dead start. The input to the room will take much longer. Deciding what room temperature to set for will be trial and error if you want the warm toes effect. The option of a wall heater is one I have been through as well. I cannot recommend low positioning of hot wire types due to the risk of towels dangling into them. If you have enough secured wall space fine, but I had one client that promptly put a bathrobe hook above a heater I restored to life. At least the belt tip was the only victim. Smelled awful.

    In the new build, I forwent all embedded electric floor systems largely due to excessive installed costs as well as the never certain sensor life. Building a bit past PGH standards has allowed all interior surfaces to equalize within a few degrees of our nominal 70F thermostat settings. While a 70F tile floor does suck the heat out of your feet, that proves an advantage in the summer. In winter, area rugs or socks keep the cold at bay.

    As the resident renegade with all resistance heating, I can say that the 150w cove heaters I have in each of three bathrooms have been fine. No noise, no fuss, no maintenance. I did look into the infrared heaters commonly sold as patio heaters. These have a large visible light output and radiate much aggressively than the cove heaters. If you don't mind the orange glow and have circuit capacity, these might be an option that can be place above all towels and robes. I would have had actual experience with them, but the client balked at the initial cost and the wire run.

    My Dad put in radiant ceiling panels back in the 60's when nuclear energy was going to make electricity too cheap to meter. They were disconnected in the 80's. Very poor performance overall for lots of reasons. Being tall was not an advantage. Verrry, verrry slow to heat things. If you have a very well insulated bathroom maybe, otherwise you will find the warm humid air from showering much quicker to warm things up.

  5. this_page_left_blank | | #5


    Citation needed for this claim:
    "cold bathrooms are moldy bathrooms"

    I asked my microbiologist wife about this, and she is skeptical. Lowering the temperature will slow the growth rate. The drop in temperature will cause a rise in relative humidity, and high humidity is certainly a factor, and potentially a bigger factor than temperature. But let's do a sanity check here and look at some practical numbers. Let's say your house is maintained at 70F and 40%RH. If your bathroom, with the same absolute humidity as the rest of the house, is a few degrees cooler, say 65F, then the RH in there will be 45%. Is that going to result in a significant increase in mold growth?

    I found this nugget at the FSEC Energy Research Center website:

    "The vast majority of mold species require “water activity” levels that are equivalent to material equilibrium moisture contents corresponding to relative humidities of at least 70%. In fact, the great majority of serious, large mold outbreaks inside buildings occur where porous, cellulose-type materials have literally been kept wet by liquid water or sustained condensation."

    I would agree that if you already have a moisture problem in the bathroom, a lower temperature could exacerbate the problem due to raising the RH even higher in the >70% range. But it doesn't seem like it will, in a well built, properly ventilated bathroom, pose any increased mold risk.

    1. Expert Member
      Akos | | #7

      No citations, just experience. I'm in the land of un-insulated double brick construction. Generally bathrooms in the middle of the house are fine, any bathroom on the outside corner will have some mold in it. It doesn't mean it is covered in mold, but when you pull the walls back, there is always some mold.

      With new construction this is less of a concern. Even there drywall+interior air film are R1.1 so just behind the drywall will always be a bit colder than the rest of the room. Add in there a shower or two per day and it doesn't take much to get near mold growth support.

      Warm bathrooms are comfortable, as long as the bathroom is inside the heated envelope of the house, the heat you put in there doesn't get wasted. There is no energy penalty in keeping it warmer. For example, I keep my bathroom at 25C (77F). This means that during the shoulder season, most of the house heat is from the bathroom, the rest of the zones barely call for heat.

  6. Robert Opaluch | | #6

    Here's a cheap and easy solution...use a heat lamp for quickly heating a small area, such as a small bathroom or part of the bathroom.

    I put fan/light units over the toilet in two bathrooms during new construction. In the winter, I'd use a heat lamp for the light bulb instead of the typical floodlight bulb in the fan/light unit. (There also was vanity lighting for general lighting. Heat lamps produce red colored light and heat.) The room would heat quickly, particularly the toilet seat or anyone sitting on it. Worked quite well in the winter. Switched out the heat lamp for a standard bulb in the summer. You could use other fixtures to use a heat lamp to heat the room, but good to point the heat lamp toward the toilet, shower/tub, or wherever you want to warm up the fastest/warmest. Caution: You can't leave a heat lamp on continuously, too much heat is directed in one area, and it should be located where children can't touch the hot bulb. But it can warm a small area within minutes.

    My young son was a big Star Wars fan, and the red color lighting from the heat lamp was a sign that the Dark Side was in control this room! He thought it was great! :-)

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