> >
>

# thick subfloor w/ radiant heat?

#1
04-03-08, 03:12 PM
Member
Join Date: Mar 2008
Location: USA
Posts: 27

my tile floor in my kitchen has a somewhat thick subfloor, layered in areas to shim and level the floor. I want to put under-floor hotwater radiant heat but am worried that the thickness of the subfloor will not be as efficient.
Its an old house, so the original floor boards are about 1/2-5/8" thick, in addition to an extra 1/2" on about half the area to help w/ leveling. thats not including the 1/4" cement board.
How much heat am i gonna lose through all the flooring? Will it take longer to heat? Thanks
-Ryan

#2
04-07-08, 06:53 AM
Member
Join Date: Nov 2001
Location: USA
Posts: 1,873
Radiant heat is dependent upon the temperature of the object. The hotter the object is the more heat that object will heat. Heat Loss is determined by the amount of heat going to an unconditioned space from a conditioned space. So the thickness of the floor is not a determining factor to heat loss, nor is it a factor on its effectiveness. Once the floor reaches a temperature above room temperature, it will radiate heat.

What will influence the effectiveness of the radiant floor system is the amount of heat loss below the floor. In other words, the installation of a "Radiant Barrier" and insulation under the radiant floor system reduces the heat loss and increases the effectiveness of the radiant floor system.

#3
05-07-08, 05:21 AM
Member
Join Date: Apr 2008
Posts: 5
This thread touches on my exact question, I am hoping to install underfloor hot water radiant in my house as well but one contractor has said it won't work in my older house because of the thickness of the floors. I have many flooring surfaces but the thickest is places with two layers of 3/4" plank subfloor and a layer of oak hardwood on top of that.

The contractor said that because of the thickness I would have to run the water at such a high temperature that I would lose efficiancy on the boiler.

is the situation the same, that once the thermal mass of my multiple layers of floor is up to tem, then the system will function fine?

If so, are ther any specific types of transfer plates or diameter of tubing that will make it more or less efficiant with such thick floors?

#4
05-07-08, 07:47 AM
Member
Join Date: Nov 2001
Location: USA
Posts: 1,873
There are two things you have to consider. One is that heat energy just like electricity and water will always seek the path of least resistance. The other is when it comes to different temperatures of objects, the greater the degree difference, the greater the attraction.

Your heating contractor is not taking the time to properly explain the consequences for exceeding the manufacturer's recommended operating temperature. Rather he/she took the easy way out. The truth is Steady State optimum hot water boiler temperature is 180 degrees Fahrenheit. The operating temperature of radiant systems is 110 degrees Fahrenheit.

Your situation is somewhat different than the other case because of the multiple layers of flooring. Each layer possess the ability to resists heat flow (R-value). For example, let's say each layer has an R-value of 3. Four layers equals R-12. You install R-4 under the radiant system. There would be greater heat flow to the basement/crawl space than to the room above the radiant system. If we compound this that there will be a greater temperature degree difference between the basement/crawl space than that of the room above, the radiant system would be ineffective.

While the ideal situation would be to remove the multiple layers, you could increase the resistance of heat flow to the basement/crawl space. The R-value of the insulation under the radiant floor system would have to be more than double that of the multiple layers.

#5
05-07-08, 10:06 AM
Member
Join Date: Apr 2008
Posts: 5
Thank you for the prompt response...

so if my floor joists are 8" in the basement, I have to leave 1" air space from what I understand, under a staple up application. Then a foil faced insulation (if I can find it) and perhaps another 3" of unfaced insulation... I could acheive an R-value of something like R-20 If I recall. probably still not enough to make a radiant system effective?

I'd have to know the r value of three layers of wood.

system could potentially work though between teh firt and second floors, as the heat differential wold be less, Maybe?

Basically, the firts floor is gutted to bare ceiling and studs, second floor still being lived in. Radiant appealed because of the comfort and the fact it could be applied to the uexposed floor of the second floor from the gutted first floor without disrupting life too much on the second floor.

So maybe I'm back to simple hydronic baseboards.... :-/

#6
05-10-08, 04:05 AM
Member
Join Date: Mar 2008
Location: Northeast
Posts: 43
Originally Posted by Wideguy
So maybe I'm back to simple hydronic baseboards.... :-/
Look into a product called Zmesh. It will solve all the problems you stated and be 100% efficient. You can also get running costs by zone to dispell the "OMG and electric system, you're crazy" scenerio. We have it installed as primary heat in many locations in New York where we pay .15 per kilowatt hour with no ill effects on the electric bill.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off