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I have a 1600 sq. ft. wood shop that I heat with forced air L.P. & wood. I would like to put in floor water heat in the building. Here are the facts:
1. Post Frame building
2. 5″ concrete floor
3. 11′ cieling hieght
4. No insulation under concrete
5. Walls & cieling very well insulated
6. Location is northern Wisconsin
This is my plan:
1. 3/4″ Radiant tubing fastened to concrete floor
2. L.P. high efficency water heater for for heating the water
3. 2″ of concrete poured over tubing
I thought that if I did not insulate on top of concrete that was already in place, the tubing would help keep it warm & avoid the problems of the old concrete freezeing & haveing the frost heave it & possibly cracking it. Any help would be very helpful.
Replies
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Dave, I think you need to save up about $3500.00 more and do the whole thing the right way. I'm afraid you would be very disappointed with the results of your current plan. I'm assuming that you have a "pole" building, where the slab doesn't support anything...it just acts as a floor...(is that correct?) I'll run through a few items for you to consider.....
You shouldn't try to heat a slab with no insulation under it. You will just be heating the ground under it for nothing. It would cost you about $1000 to get the existing slab removed and hauled away. I would imagine you could find a place to dump it without paying landfill charges.
Installing styrofoam under and around a new slab would cost you $600-$700. The additional 3" of concrete would run you less than $1000. The cost of pouring 2" or 5" is the same as far as labor goes, so that is a wash.
You will need to use 6x6 wire mesh in either floor because I don't know of any other means of attaching and spacing the wire under your plan.
Using a conventional water heater is not a good idea. It is not cost effective. Once these slabs get warm, they may not require additional hot water for hours, but your heater is sitting there warming 40 or 50 gallons of standby water for nothing. There are many kinds of very efficient little wall hung-direct vent units that are built just for this application. L.P. gas is not cheap, and you have to be very efficient. Doing this right the first time will more than pay for itself in comfort and fuel savings.
*Dave: there's a discussion about insulation or not in "radiant floor heating - created by Nick" messages 10-12. While I agree with the "you should only do the right way" crowd that insulation under the new slab is preferred, it is an economic trade-off. Should I invest $700 in insulation to save future energy costs or put that money in my checking account and earn 1.25% on it? Duh. Insulate. But should I insulate or put that money into Microsoft stock and realize 50-90% appreciation/year? Duh. Buy the stock. We all have different financial situations, different comfort with risk, and different ideas about the future (energy costs, Bill Gates' continued success. etc.). So maybe there are different correct answers to the economics of building. A 1600 square foot building gives you relatively little perimeter to surface area - so the edge effects won't be huge if you don't insulate (assuming the building is 55x30 and not 160x10). On water heater choices: the standard domestic hot water heater is about $150 and, about 75% efficient (knocking it down a bit for continued air flow up the flue as G. LaLonde points out but crediting it a bit for lower teperature/more efficient operation). Versus the spiffy direct-vent 94% water heater for $2300. If you've got good, but not great insulation; propane is $1.30/gallon and I'm guessing 6,000 heating degree days, the energy cost would be $1,195/year for the cheap water heater and $944/year for the 94% heater (ignoring it's need of electricity to run a small fan). So the cheap heater saves you $2,150 initially but the expensive heater saves you $250/year thereafter or payback in 8 years. So if you carry any credit card balance or own Amazon.com stock - go cheap on the shop and pay off the plastic and keep the stock in your portfolio. But if you have thousands sitting in a mattress - go whole hog on the energy efficiency. -David
*David, You know as well as I, that you should invest first in your shop, and then worry about other ways to spend your money!
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G Lalonde,
My reasoning for not insulating under the slab is that we have done a number of homes that have elctric heat cables buried in 6" of sand beneath the slab with the only type of insulation required is 2" around the perimeter, the sand acts as a thermal mass & stores the heat so that the heating coils only fuction on off peak electric. Home owners report great results.
I thought that since my slab is setting on a sand gravel base that it would act as heat storage as long as I insulated the perimiter.
L.P. Gas in this area has always been the best heating value. the last few winters I have been locked in price of $0.56 a gallon.
I have seen some smal shops in this area that are using High efficency water heater as a cheap altrenative($450.00 as oppossed to $1750.00 for
boiler).
If the sand acts as thermal mass why remove the concrete. The way you explained things was the original plan I had, but just exploring different ideas. Thank for reply and anything additonal
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David, Actually,I was just kidding you, but as long as I've got your ear.........The price of L.P. in northern Wisconsin often reaches $1.00 or more and last year was almost $1.25 for a while. My theory is that I can insulate a slab to any degree that I feel comfortable with, but have no control over heat loss in an uninsulated slab.
I am also concerned with his idea of pouring only 2" of regular concrete over another slab. This seems like a setup for a cracked floor.
I know people with insulated and uninsulated slabs. The ones with the uninsulated slabs did so because the concrete people were scared to try something new and pour over styrofoam. The insulated slabs are much quicker to respond to heating, but things kind of even out after a few weeks. Even with no insulation under the floor, they must insulate the perimeter, so we're not talking a great deal of extra expense.
Who knows what the future will bring as far as energy costs etc. I'm just more comfortable with doing it the best way I can right from the start.
Nice talking to you!
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Why are you unhappy with your present heating system that you want to spend your money on something new?
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I have a 1600 sq. ft. wood shop that I heat with forced air L.P. & wood. I would like to put in floor water heat in the building. Here are the facts:
1. Post Frame building
2. 5" concrete floor
3. 11' cieling hieght
4. No insulation under concrete
5. Walls & cieling very well insulated
6. Location is northern Wisconsin
This is my plan:
1. 3/4" Radiant tubing fastened to concrete floor
2. L.P. high efficency water heater for for heating the water
3. 2" of concrete poured over tubing
I thought that if I did not insulate on top of concrete that was already in place, the tubing would help keep it warm & avoid the problems of the old concrete freezeing & haveing the frost heave it & possibly cracking it. Any help would be very helpful.