floor covering on slab of passive house
Trevor_Lambert
| Posted in Energy Efficiency and Durability on
How much difference does the floor covering make on solar heat retention? Intuition tells me that a stone/concrete/tile floor is best for absorbing radiation. I realise however that intuition is often wrong, and even if it’s right it might not be significant. I would prefer to have hardwood floors, but have been operating under the belief that having hardwood floor over top of the concrete is going to be a significant penalty in terms of thermal comfort and energy efficiency. I’ve recently read that in terms of in floor heat, the floor covering hardly matters. Is this the case in reverse, i.e. receiving radiant heat vs giving it off?
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I should have also mentioned, the slab is fully insulated from the ground and exterior (R50+), so insulation between the slab and the interior is not desirable.
Trevor, I'd say your intuition is pretty good--masonry is both conductive and has a high heat capacity, so it can absorb and store quite a bit of energy. Floor coverings may contribute some thermal mass, but they are also insulating the masonry from either absorbing or releasing energy. Even if perfectly exposed, though, there isn't enough heat storage in a few inches of masonry to last all that long.
Fortunately, if you have good levels of insulation, good air-sealing, and well-designed glazing--if you've invested in R-50 foundation insulation than you probably do--it doesn't really matter, as diurnal thermal mass storage shouldn't be a big factor in your heating strategy.
For more information, check out these articles:
https://www.greenbuildingadvisor.com/blogs/dept/musings/all-about-thermal-mass
https://www.greenbuildingadvisor.com/blogs/dept/musings/understanding-r-value
I'm certainly not expecting the solar heat gain to provide all the heating, but so far it does seem to be pretty significant. On a typical day, the temp will start out around 66F, rise to about 70F by about 6pm, and not drop back down to below 66 until the very early morning hours. This is without any active heat source running, and outside temperatures in the 0-30F range overnight. (The in floor heat is turned on, but thermostat set at 65). The slab is 8" thick, so maybe that makes a difference.
The hardwood floor wouldn't add significant mass, but it's also not exactly a high insulation either, somewhere between 0.5 and 0.75 R value. The source I got that from says that tile actually has the same r-value per inch as hardwood, which I find counter-intuitive.