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BTU to ccf

HvacroNY Member Posts: 1
I open up the newspaper to find natural gas is at 3.74 mm btu. My utility bill charges me in ccf's at $ 0.87. My boiler is 100,000 btu's in and 85,000 out and it runs for 15 minutes.

#1 How do you convert from mm btu to ccf ?

#2 Will 85,000 btu's really be transferred into the radiators and piping?

#3 Can I calculate/measure the btu's my boiler produced and confirm it is being transferred using the pipe size ( volume of water ) and temperature rise?

please help, this has caused a number of HEATED arguments. Thank you.


  • Jean-David Beyer
    Jean-David Beyer Member Posts: 2,666
    This won't help much.

    Lat month I used 4 ccf (400 cubic feet) of gas. It averaged 1.04 BTU therms per ccf, so they billed me for 4.17 therms. For this they charged me $3.35 for the gas and $2.09 to deliver it, and added a customer charge of $8.25, so the total cost was $13.69. Clear? The number of therms per ccf changes every month. The customer charge is constant, so when I start heating the house instead of just my domestic hot water, the customer charge will not be such a large proportion of the total.
  • CMadatMe
    CMadatMe Member Posts: 3,086

    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.
    "The bitter taste of a poor installation remains much longer than the sweet taste of the lowest price."
  • Tim McElwain
    Tim McElwain Member Posts: 4,524
    The answer

    is that there are approximately 950 to 1075 BTU's per cubic foot. The equipment is rated in BTU's the gas meter measures in cubic feet.

    On your bill it will state something like this so many CCf at say 1027, the 1027 is the actual BTU content average for the month that the gas company sent out.

    The actual transfer of BTU's into the system is called thermal efficiency. If a proper heat loss was done per room and the piping to the rooms is sized correctly along with sufficient radiation for each room then the applied BTU will be pretty close.

    Actual measurement of real BTU's would require a BTU flow meter to be accurate.
  • Brad White
    Brad White Member Posts: 2,393
    edited October 2010
    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

    "If you do not know the answer, say, "I do not know the answer", and you will be correct!"

    -Ernie White, my Dad
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