BTU to ccf

Simple

There is 103,00 btu's in a cubic foot of gas. That 3.74mm represents cost of 3.74 million btu's.

100,000 btu boiler just about burns a cubic foot on every fire. Now if it's a 80% AFUE boiler that means your sending 20% of that .87 cents or .17 cents into never ever land.



I doubt your using the entire load. You never need that entire load until you reach the coldest day in your region. You will never know the anwser without doing a heat loss of the home. Sad to say but that .17 cents is probably in reality more like .25 cents or even more.

Or another way to look at it

Gas is sold typically in Therms. A therm is 100,000 BTUs, no matter what.  But the therms are delivered in volumes of gas, measured in cubic feet over varying compositions and heat values.



As Tim pointed out, the therm content per CF does vary. Most natural gas is methane, about 95%, the remainder can be butane, ethane heptane, propane and a host of other minor players, plus inert gasses with no appreciable fuel value.  Then they toss in ethyl mercaptan as the odorant we all know and love.



The gas company buys gas on the open market and depending on the market condition, cuts or enhances the natural gas with additives. Butanes are the largest category, but if in short supply and no other additives, or whatever it is, the fuel content in therms is adjusted on your bill. Usually this is fractional, within ten percent.



The gas METER however, measures volume in cubic feet. If the presumed gas heat value is 1,000 BTUs, a therm is 100 cubic feet or CCF. So for discussion purposes, a therm is the same as a CCF.



So in answer to your questions in order:



1. To convert from MMBTU to CCF, divide MMBTU by 10. (10 CCF of 1,000 BTU/CF gas is a million BTUs. Put another way, 1 CF =1,000, 100 CF (or 1 CCF) = 100,000 and 10 CCF = 1,000,000 BTUs. That is input.



2.  Will 85% be transferred to radiators and piping? (And your space we hope!).  This can vary over time. A boiler that cycles more in warmer weather, (say the 30's), will lose more to jacket losses and start-up losses than the same boiler at zero degrees. The colder weather in this case will be more efficient. Think of the efficiency as a sliding curve, descending as it gets warmer outside from your cold design temperature. But for discussion purposes, 80-85% is doing pretty well for most non-condensing boilers. But it really does vary.



3. Can you calculate this? As Tim said, you really need a BTU meter. This means real-time and continuous measurement and logging of flow rate, temperature of the supply water out and temperature returning, all over time, usually in hours but also over a day divided by 24. This is compared to the fuel rate input.



To be proper about it, the process has to be continuous. If you fire up from a cold start, your delta-T will be wide and your space gains (what you want to do!) will be some minutes, maybe half an hour or more, away.



This is not a good time to pat yourself on the back!

You need to take into account the up-cycles, down-cycles and in-between coasting. Remember too, between firing cycles, your pump still runs and clocks delta-T over time with no fuel input. Another time not to pat yourself on the back!



My $0.02



Brad