Basement bath floor heating options?
qwkbrnfox
| Posted in Energy, Heating & Insulation on
Hi All,
We’re going to be putting in a basement bathroom into a 1912-era house, so there won’t be any insulation under the slab. The floor is pretty cool down there in the winter, even with heating on – not great for stepping out of the shower. We could put electric heating under the tile, but I’m concerned that would waste a lot of electricity, what with the uninsulated slab.
This situation has to have popped up before. Any common practice? The footprint of the bath won’t be huge – roughly 10×8.
Thanks,
Todd
Replies
Excellent question - hopefully this response will help bump your question to the top of the list and get some insightful answers. I know I'm interested...
Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
If you're just trying to keep the tootsies warm after a shower, put in electric under tile, and either use a timer or turn it on before you take a shower.. shouldn't take long to heat up.
For a basement add-on, I doubt the wasted electricity even with constant use would be particularly noticeable. It's a very small area. But I would probably use at least a programmable T-stat to just run it when it's likely I would want to use it to take a shower (mornings, evenings, what have you).
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
I wonder if some sort of radiant barrier installed below the electric heat mat would prevent the heat from going down through the slab? You may be right though, it could be overkill for such a small area. Then again, it sure wouldn't likely be much more expensive to detail the heating system to deflect upwards, right?Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
There is no such thing as a radiant barrier that is worth the money under any kind of slab product. a 1/2" of rigid foam would be twice as good. Not sure what either product would do to a tile install in this case though.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
<<
<<There is no such thing as a radiant barrier that is worth the money under any kind of slab product. a 1/2" of rigid foam would be twice as good>>
I don't follow - you say that there is no such thing as a radiant barrier for this situation, but that rigid foam would work. If rigid foam would work, why not get foil faced polyisocyanurate, wouldn't that be radiant and foam working together?Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
radiant barriers are only radiant barriers when there is radiant transfer; radiant transfer is the transfer of heat through space. No space, no radiant transfer, no benefit to a radiant barrier; this is the situation with slab installations.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
You need a about 3/4 - 1" air space infront of the radiant barrier for it to be a radiant barrier. Otherwise it just conductive heat transfer if direct contact or through the air if there is only a small gap.I wonder how much Ditra would help in a case like this. I realize that it is not much but any little thermobreak would help.Of course one could always cut out a section of slab and put foan under it.
hmmm, well that certainly makes sense - thanks for the clarification guys.
But if you need an air space for a radiant barrier to work properly, then what is the benefit of staple-up radiant heating with the foil facing? If teh heating elements are right up against the foil, I don't see how they could be doing much - well, according to what you all are telling me, at least.Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
Thanks for the input! All good ideas. I've got to jack hammer up part of the slab to run the plumbing. Depending on the layout (the toilet and shower in particular) this could be a substantial part of the area of the room. If I follow Bill's idea and blast out the entire area, is there issues with tieing back into the old slab? This opens up the possibility of having a small radiant zone - the boiler is about 10' away.Thanks,
Todd
It shouldn't touch. If it does, it's not helping as much as it should, though I'm sure there is some oblique angle radiant energy that is being reflected, it's not being used "properly".I use quotes there though because I personally don't believe in using radiant barriers in joists either; radiant barrier insulation relies on reflectivity. Joist bays are rarely clean for long, IMHO, and so I don't trust them to remain reflective forever. I'd much rather have real R-value in the joist cavity than a shiny surface that may or may not remain shiny.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Ah damn, where's Andy Engel when you need him... I just had a conversation with him the other day about this very topic. He was telling me that the cleanliness of the radiant barrier materials don't matter much - but that was with radiant barrier sheathing, which may or may not be a different animal.
Let's see if he meanders by this thread, perhaps he can weigh in.
by the way...sorry to hijack the discussion - I was interested in the techniques for heating a basement bathroom...Justin Fink - FHB Editorial
Your Friendly Neighborhood Moderator
I'd be interested in any information that could improve my understanding as well, if you run into him, point him here!-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Rob, your understanding is correct, as far as it goes. Radiant barrier sheathing is a different animal. If you aren't familiar, it's intended for roof sheathing and has an aluminum foil coating that is installed facing into the attic.
Here's the thing though: Radiant barrier sheathing isn't intended to reflect radiant heat. I suppose it could, but in its specified application, that reflection would be inward. The aluminum is a low-emissivity coating, like that used on window glass. As the roof heats up from the sun, this low-e coating emits only about 5% of the energy it absorbs. It does require an air space below to minimize conductive transfer (and you'll always have some of that where the sheathing hits the rafters).
Hope that helps.Andy
"Never try to teach a pig to sing. It wastes your time and annoys the pig." Robert A. Heinlein
"Get off your dead #### and on your dying feet." Mom
Ah, very interesting. I see what you're doing then. thank you very much for the clarification!-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Please don't let folks put regular foam directly under a tile floor because the deflection may cause the floor and grout to fail. One foam backerboard that is designed to handle floor loads under tile is called Wedi board. It's been used for a long time in Europe and you can buy it in the U.S., but it can be difficult to find. See below.
http://www.gstallc.com/documents/FAQ.pdf#search=%22wedi%20board%22
http://www.wedi.co.uk/using.htm
http://www.wedi.de/usa/products/comparison/product-comparison-detail.php
http://www.warmlyyours.com/homeowner/wyuniversity/whatsnew.aspx
http://www.wedi.de/usa/wedi_partner/representatives.php
Billy
Edited 8/17/2006 12:57 pm ET by Billy
Edited 8/17/2006 1:04 pm ET by Billy
Edited 8/17/2006 1:19 pm ET by Billy
Edited 8/17/2006 1:21 pm ET by Billy
Edited 8/17/2006 1:23 pm ET by Billy
A couple of things....
First, any kind of insulation makes a big difference, as does the selection of the flooring material. Rubber tiles - as used on shop floors- are a lot more foot-friendly than bare concrete.
The 'poor man's' floor heater is mounting a heat lamp in the ceiling, shining down onto the floor.
A fancier solution is sold at your local electrical parts house; there are various firms making custom electric mats that are installed in the mortar, under the floor tiles.
Note for the editor: installing such a floor is a good project for Clifford Popejoy; you need to use a "megger" at various points in the project, and he seems to like using such fancy toys! :)
http://www.speedheat.us/rug_buddy.htm
Troy Sprout
"Work is the curse of the drinking classes."
Oscar Wilde
There's a lot to be said for a rug, in terms of comfort, low price, and simplicity.
I have a NuHeat electric mat with the built in timer/thermostat. I think the electric usage is fairly minimal, but the catch is that we use this everyday so the programming works for us (and the cats love it). NuHeat will custom cut the mat for you in advance, and it only takes about 10 days total.
If your shower is for occasional use, then you have to remember to turn the heat mat on in advance.
We also have a towel warmer from Runtal. Way nice to have toasty towels.