Yesterday I started feeling pretty lousy at in the afternoon, with the same symptoms of the cold that plagued the crew this past week. Drat!
Given that I was feeling under the weather, today felt very busy although it wasn't really. We met with Heinz the cabinet maker yesterday evening, and although we had a very good idea about the handles, we needed to finalize the laminate counter tops selection for the main bath and the laundry room. So today we went to the kitchen design center and selected Formica Madras Indian Slate.
On the way back we went to the Orange Borg to pick up the sink and faucet for the powder room which had arrived. While we were there, we checked out the cabinet handles as well as the undercabinet lighting. Since Freda wanted a special knob (knob A on this page) from Lee Valley for the laundry room, we popped over there to pick these knobs up. There is no other brass colour in the house other than these knobs.
Last week I calculated how much energy would be required to heat up the slab. Unfortunately, the house was not closed up and heat turned on before it got quite cold. Now the themal mass of the concrete floors are working against us, as we have to heat up all that concrete. These are the calculations I did then. I think you can follow along with reasoning.
Mass of concrete
23 cubic meters of concrete for both main floor and basement floor. This translates to 30.08 cubic yards per floor. One cubic yard of concrete weighs 4000 pounds, each floor has 120,000 pounds of concrete (60 tons) to be heated.
Temperature differential
Let's assume the main floor is at -5C, and the basement floor is +2C. Let's further assume that we want to get the floors to +15C, which would be a temperature for working in, drywalling, etc. This means we need to heat the main floor by 20C and the basement by 13C.
Energy (BTU) cost
1 BTU is the energy required to heat 1 pound of water by 1 degree Fahrenheit. Lets assume that this applies to concrete also. So we have to convert the Celsius temperature diff to Fahrenheit and multiply by the weight of the concrete.
20C transition is 36F (main floor), and the basement 13C is 23.4F. Multiplied by the weight of the concrete, we get a requirement of 7.1 million BTUs to heat up both slabs.
Heating efficiency
However, since the main floor slab is below freezing, the water would freeze in the pipes if we ran the hydronic heating first -- this would not be a good thing. Since we need to heat the air first to heat up the slab, we are not going to get great efficiency as this is not as efficient as direct heat transfer through the hydronic system. For now, let's assume that the heating efficiency is 60%.
Propane requirement
Propane has 91,000 BTUs per gallon. Given the BTU requirements (7.1M), and heating efficiency (60%), we come up an estimated 131 gallons of propane(US gallon) to heat both slabs to 15C.
Do we have enough propane?
We should have had 3 big tanks delivered, but they only delivered two. The three tanks hold 1100 litres, so our two tanks should contain about 733 litres. Converted the estimated volume of propane required into litres, we get 495 litres required.
So we do have enough propane in the big tanks, although it will use about 70% of the tanks' contents. This translates to a cost of approximately $400.
It really is too bad we weren't able to get the vapour barrier on sooner so we didn't have this extra expense.
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