Electric Radiant heating on slab

lalitharJune 3, 2011

Hi,

Our house is on a concrete slab and I want to understand the options for installing electric radiant heating on slab. I hear these have come a long way and there are ultra-thin mats available. Any advice on what to look out for, brands, sizing, any issues? Can we do room specific controls? We are thinking of doing tile or hardwood flooring. I searched the archives but could not find anything specific to my question.

We live in California near San Francisco, so not terribly cold but cold enough.

thanks

Lalitha

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david_cary

Electric radiant heating is generally used for small spaces like bathrooms. To do a larger area is a very expensive undertaking and even more expensive to use. The thought of doing that in CA is particularly insane....

Why insane? Well your peak rates are 4 times mine (maybe not but most of the Bay area is). and I wouldn't do it here because of the expense.

Makes far more sense to do hydronic and heat with NG. But any slab heating for a large area is really overkill in such a temperate climate. What do you heat your house currently with? Are you trying to heat your house with radiant heating (because that isn't really possible with electric) or are you just trying to take the chill off the floor?

Normally electric is used for taking the chill off of tile. Since you mentioned wood, I am guessing that you want to heat a room with this...

    Bookmark   June 3, 2011 at 11:49AM
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davidro1

i'd like to add a few points.

A slab is a thermal mass bigger than an elephant.
Concrete is a heat sink.
You do get all the heat back, if you own both sides of the slab.
In that case a concrete slab is a heat source as well. A governor.
Here you don't have that.
A slab on grade is connected to mother earth.
The more it acquires heat (from any source above), the more it loses heat to the ground underneath.
The more you try to heat it, the more you spend on heating the earth underneath.
That is a lot of mass.

This explains why seeds germinate next to rocks.
The rocks acquire heat from the sun and re-radiate that heat into the ground, triggering germination.

Your slab on grade might be on earth that is generally dry and warm. Or not.
The more moisture in the earth, the more slab heat is lost to the earth. More quickly.

It may be easy to have a warm floor on a warm slab on grade. Do nothing more than install wood on an underlayment.

It's difficult to turn a cold wet slab on grade into a warm floor.
A layer of really good insulation is required.
Now, you are walking on a raised floor.

Since you asked about the new and thin electric heating cables, I'll guess that you can't raise the floor by much.

    Bookmark   June 3, 2011 at 12:31PM
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davidro1

To get a warm house in the geographical area you are, think of making the house airtight with a housewrap, building it as they would in Alaska or the Yukon. Almost every house in the SF area feels cold in winter, and almost every house 1000 or 2000 miles farther north feels warm in winer.

    Bookmark   June 3, 2011 at 5:33PM
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