Figuring gas cost for heater


Well-known member
Sep 15, 2019
I’m considering buying a 400k master temp heater. Out of curiosity I would like to know how much it would cost in gas per hour to run the heater. Is it true that 1000 BTU is equal to 1 therm of gas? Where I live in New Jersey it cost $.79 per therm which includes the supply and delivery charges. Is it realistic to say that to figure out the gas cost I would multiply 400 x $.79 which will give me the hourly rate? 400x.79 = 3.16 p/hour.
I’ll also need this calculation to figure out the cost to run 2 fire bowls at 65k BTU’s each.
Thanks everyone for your help.


Gold Supporter
TFP Guide
Jul 21, 2013
Northern NJ
Pool Size
Salt Water Generator
SWG Type
Pentair Intellichlor IC-60
I think you have some typos in what you wrote but get to the correct answer.

1 Therm = 99,976.13 BTU = round up to 100,000 BTU

Running your 400K heater is 4X.79= $3.16/hour
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TFP Expert
Mar 2, 2011
I was just thinking, don’t I have to deduct for the efficiency of the heater?
A 400,000 btu/hr heater uses 4 therms per hour regardless of the efficiency.

The efficiency only tells you how much of the heat transfers to the water.

The gas company does not care how efficient your heater is.

They only care how much gas you use.


Bronze Supporter
Sep 23, 2015
Here is a spiffy calculator (spreadsheet) to help you figure out the cost:
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