btu's required

David Van Wickler_4

For those typobaiters - bite me. I don't have time to correct typos. Me is graduate of college edookation.

R-1.1 for condution heat transfer is only part of the story whencomparing buble insulation to rigid insulation. But that's another day I suppose.

High water table - killer downward heat loss.
High infiltration of outside air. Killer

What is the electric rate per KW/hr and is there an off-peak rate as well.

Unless your paying about $.03 per KW and your electricity comes from hydropower, electricity is cheapest to install and most expensive to operate.

Although the water heater converst 99% of the energy it consumes into BTUH, the efficiency of the total system (generation, transfer, conversion - Xfrmers, etc) bring the delivered efficiency to probably 15-20%.

Propane/nat gas condensing boilers/water heaters convert the fuel to over 90% useable BTUH.

mitchb B

having a debate

Situation...radiant floor heat. 4" insulated slab 1800sf, 7 loops in 5 zones on 12" centers. insulation is R8 foil faced bubble insulation under the slab, 2" extruded at the edge.

I did not install, this is a call in as the system is using an electric boiler and the bill is high.

One thing I need to calculate is the btu's required to heat the slab to see if the numbers are out of line.

Does anyone have the information of required btu's to raise 1 cubic foot of concrete 1°F? I can blow it up from there.

Thanks.

Mitch

ALH_4

Fuel cost

Heat capacity is only a small part of the picture. Concrete is approximately 0.2 btu/lb-°F.

The most important factor at this point is the cost of electricity versus the alternative, taking combustion efficiency into account. Siggy's book has a good description of these comparisons.

bob_46

Specific heat of

concrete .27 Btu/Lb/F*.

Ron Gillen

Insulation?

What kind of fill is under the slab? That's where the heat is probably going. Bubble under slab is maybe R-1.

mitchb B

Thanks

Thanks guys for the information. .27 was what I needed.

I agree that bubble insulation under concrete is trash...we may drill a core sample with a 3" core bit to see what we got.

Electricity costs for the area where this is is one of the cheapest.

Again I appreciate the help.

Unknown

been a long time

but I'll bite you if you insist.

All these rates to rase concrete, I thought it was 264BtuH per cubic foot.

Ooops.

wheels

ALH_4

Heat loss

But that 0.27 btu/lb-°F is only the heat to initially warm the slab. Heat loss from the slab is different. The downward heat loss can be affected by many factors, as mentioned already.

Maybe I am missing the point completely here, but the best way to compare what the heat bill is now to what it would be with another fuel is to take the electricity use on their utility bills for the past year, and compare that to what the same amount of energy would cost with other fuels. You have the advantage of already experimentally knowing the heat loss as the system and structure stands currently.