Radiant heat on top of existing concrete?

taftJune 23, 2011

Would there be any issues with installing a radiant heat floor on top of an existing concrete floor as long as the existing floor is in good condition, or is this a bad idea because I would want the new finished floor to also be concrete but would a wood floor be a better choice in this situation or it doesn't matter?

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don92

Not quite understanding the question. Are you saying electric radiant heat strips with thin layer of concrete on top? The heat strips will go anywhere,The're not the problem, your concern should be with the condition of the existing floor, a bonding agent, what concrete mixture you use and the thickness. You need to give us more info and what you want to accomplish before we can give a good answer.

    Bookmark   June 26, 2011 at 8:33PM
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taft

I was actually thinking of the radiant heat tubing in the floor but perhaps in this situation the heat strips would be a better choice and not add additional thickness that isn't necessary.

But yes, the plan would be to add the radiant tube/strips, then cover that with concrete so the finished floor is stained concrete. I like the practicality of a stained concrete floor; easy clean, little worry about damage from pets/kids.

    Bookmark   June 27, 2011 at 8:39PM
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don92

I do a lot of tile over heat strips but have never used it under poured concrete. You would want to keep it as thin as possible so the heat has less to travel through. Probably a self leveling compound with polymers would give you the strength you would need and still keep it under an inch but have no idea as to how it would stain.

    Bookmark   June 27, 2011 at 9:46PM
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taft

Thanks for your suggestion's, Don.

    Bookmark   June 27, 2011 at 11:41PM
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davidro1

hgtvme describe the slab in question. Is it high and dry or is it in a deep basement in a relatively wet location in a relatively rainy climate? Things like this make a huge difference. The idea that you might heat only the top layer is not a good idea for the general case, except for the initial minutes or hours after you turn it on. Heat DOES travel through the entire slab when you leave the heat on all the time. Heat loss does occur, all the time. Your slab and its "environment" will determine this loss and the rate of heat loss. This then determines the sense of comfort or discomfort you may feel when walking on the slab in bare feet or in socks or in shoes. This also determines the cost of heating the floor and the wattage required to get the effect you wish. Question: what is worse than a cold concrete floor? A heated concrete floor that doesn't work as well as expected.

    Bookmark   June 28, 2011 at 10:21AM
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don92

My clients that put radiant floor heat on their slabs are not looking to heat the room, just warm their feet. Warm feet warm body. The wattage used by keeping it on 24/7 is minimal and the heat loss is of little concern when you have happy feet. I have covered entire rooms with the strips to heat a room and it does fairly well but I would not make it my primary heat source.

    Bookmark   June 28, 2011 at 6:47PM
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taft

Hmmmm, you guys are making me rethink this plan. I had not considered that there wouldn't be insulation under the existing concrete floor so there would be heat loss and yes, I would use the radiant floor heat as THE heating system in this house.

The only way to get around this would be to hammer up the existing floor and install a new one with radiant heat tubing. More expense in many ways...have to put pen to paper.

    Bookmark   June 29, 2011 at 3:06AM
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tiefsa_yahoo_com

It's possible to do a hydronic system on top of a concrete slab already. You bolt the PEX radiant tubing down to the existing slab and then pour another layer of concrete over this. I've seen it done. The only negative is you loose some ceiling height.

Here is a link that might be useful: Hydronic Radiant Heat on a Concrete Floor

    Bookmark   June 29, 2011 at 7:44AM
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davidro1

hgtvme there are many slab floors without insulation that can be heated. Keep studying.

    Bookmark   June 29, 2011 at 1:33PM
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GreenDesigns

Electric radiant floor heating is to warm the feet, not the room. If you plan on heating the home, pex tubing and some type of boiler is what you need. And sure you can install hydronic radiant heat tubing on top of an existing slab, but unless that slab is insulated, you're going to have constant heat loss to the soil and air where the slab is exposed to the elements. If you live in a moderately cold environment, the heat loss might not be so severe as to cost you that much money, but if you live in an extreme cold environment, your boiler may not do such a great job keeping you warm.

Other than the heat loss to an uninsulated slab, the biggest drawback is the slow reponse time to change temperature. You're heating up a large radiant mass, and if it suddenly warms up outside, the home will be too warm and take several hours to cool down. The opposite happens if you are having a warm day, but it's cold at night. It takes time to come up to temperature. You learn to adjust to these quirks and how to use the thermostat to manage the temps most effectively, but if you are used to the instandt response of forced air, you may not care for radiant. If you're used to radiators, you've already got most of the temp control methods already figured out.

    Bookmark   June 29, 2011 at 11:22PM
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davidro1

some of the above is true.

A slab in a basement loses X heat to the ground. This is a function of the slab and the ground, but the climate is not a factor.

The heat that goes from a heated floor into the house is real heat not nothing, and it reduces the amount of heat needed from the other heating systems that the house may have. It CAN be a lot more than simple foot warming. It's all a power game, it's all about power. Saying it only warms toesies is highly non-specific and not worthy of a professional. However, this being an existing concrete floor, you are probably not expecting to use floor heating as the sole heating system (That is wise), so the whole question of toes-or-house is moot.

    Bookmark   June 30, 2011 at 11:56AM
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rsc3441

I know this subject old, but hopefully someone is still "listening."

We have a finished basement in an old brick shoe factory (built around 1890). We just ripped out the hardwood floors (which were on top of a plywood subfloor), so now the concrete slab is exposed.

We want to install ceramic tile throughout, and are thinking of also installing a hydronic radiant heating system.

My questions:

(1) should we install some sort of insulation over the concrete slab but underneath the radiant heating system in order to minimize heat loss? I

(2) if "yes," to #1, then what type of insulation?

(3) If "yes," to #1, should we be concerned about mold growth on the insulation in the case of flooding in the basement (from a burst pipe, for instance)?

Many thanks!

    Bookmark   July 16, 2014 at 5:34PM
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Alex9876

Anyone may suggest the best way to insulate over existing slab with minimal loss of ceilling hight? Any thoughts on Roth panels? What about 1" rigit insulation under Warmboard? I would really appreciate any advise.

    Bookmark   August 16, 2014 at 11:16PM
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