what is the cost of natural gas for an on demand hot water heater to raise 10gpm 80 degrees F?

3 Comments

1. Hawking Sucks says:

   November 5, 2009 at 4:13 am

   to answer your question, you would have to know how much usage the water heater gets.

   To get the answer though, you can use the equation 5*(gpm)*(delta T) to get the BTU/h to heat the water up. You take that number and divide by a combustion efficiency. I would guess around 80%, but you would have to get that number specifically from a water heater vendor. You would then have to multiply that by the usage (in hours) to get BTU’s. Covert that into mmBTU’s (thousand BTU’s) by dividing by 1000. Assuming the dollar figures above are correct, you then multiply that by $9.08/mmBTU’s to get the cost to operate a water heater for one year.
2. harddrive2002 says:

   November 5, 2009 at 4:13 am

   natural gas cost is around $8.75 cubic yard now, from there I don’t know how to do the math. it should say an approx. annual cost to operate on the tank.
3. chemical_engineer2006 says:

   November 5, 2009 at 4:13 am

   If the flow of water stays constant at 10 gpm for 1 year, at the current cost of natural gas at $9.08 per million btu, the total cost will be:

   $31,841.77

   ($9.08/MMBtu)*(1btu/lb*F)*(80F)*(10gal/min)*(8.34lb/gal)*(525,600min/year)

   To simplify this, at the current natural gas cost and a constant flow of 10 gpm and a delta T of 80 degrees, the cost per minute is:

   6 cents