[TheForge] Re: WAAAAAAAAY OT (while we're talking about heat

[Gladish Family]

Justin Fellenz wrote:

>>Andy and Frosty and anyone else with in-floor radiant heat, 
>>   
>>  Do you have insulation horizontally under the slab or no? I'd like
>>to avoid it since it's expensive and it sounds like it makes it more
>>likely the slab will crack under hard (power hammer) use. I'm told
>>you need it but it seems to me that insulation vertically on the
>>fronst walls 3' deep should isolate the 6" of crush and 3' of earth
>>pretty well. 
>>   
>>  JRF
>>    
>>
Justin, I think you'll be fine.
My introduction to in-floor heat was a friend in northern Michigan who 
made his own stupid-simple system. Here's what he did.
He laid 4' foam sheets (2" if I remember correctly) on the ground inside 
the foundation of his home, so the outer 4' of his slab was not in 
contact with the earth. He attached foam to the inside surface of his 
foundation so that the heated slab would not be in contact with the 
foundation. The rest of the slab, the main interior area, was directly 
in contact with the sandy ground.
After the slab was poured and pretty well dried out, and the house was 
dried in and insulated, he started up the heat source: a 35 gallon 
electric domestic water heater, available at a hardware store near you 
for about $150. He was shocked when the first month's bill was over $200 
(this was in 1989) but the next month and all succeeding months the bill 
stayed around $35. Phenomenal for that part of the USA.
He can leave the house unheated for up to three days when the 
temperature is between 0 and 25 degrees F. and still come home to a warm 
house, though there is a dip in indoor temp while the system catches up.

I have part concrete and part soil cement slabs in my house. The soil 
cement slab has foam underneath and I would definitely be more careful 
in the design, as parts of the floor have subsided a little where the 
foam settled....maybe I was careless in bedding the foam, hard to say 
now- it's not particularly unsightly, but it makes the coffee table 
slightly tippy.

For some reason code in our area allows the use of an air bubble blanket 
under heated slabs. This is available from plumbing supply houses in 
large rolls, and is extremely simple to lay and removes the need to 
spend a lot of time making sure that foam boards are perfectly flat on 
tamped sand.
My first choice for a shop slab would be to lay this material down, and 
be sure to insulate the perimeter of the slab so that there is no direct 
contact between the slab and the foundation, since that will suck the 
heat right out of your slab.
A 4" slab with fiber-strand mixed in will be tougher than you will need, 
though you may want to make a block foundation for any particularly 
large hammers.

Best of luck, and let me know if you have any questions...all my info is 
based on hands-on experience, I'm way short on abstract theory...

A.G.