I'm not sure whether this is the correct forum for this question, but here goes...
I've got an electric 40 gallon water heater and was considering replacing it with a 40 gallon propane water heater. It seems that most people in this area believe propane is a much better way to heat water, but it seems to me that propane will be more expensive.
Here's my calculation.
BTUs
------
per gallon of propane: 91500
per kwh of electricity: 3412
Efficiency ("energy factor")
-------------------------------
40 gallon electric water heater: ranges from 0.9 to 0.95
40 gallon propane water heater: ranges from 0.59 to 0.67
Let's suppose an electric water heater has an efficiency of 0.9 and a comparable propane unit has an efficiency of 0.67 (note that I'm taking the low number for the electric and the high number for propane, which should skew the numbers slightly in favor of propane). Then
"Effective" btus when heating water
------------------------------------------
per gallon of propane: 91500 * 0.67 = 61305
per kwh: 3412 * 0.9 = 3071
The ratio here is 61305 / 3071 = 20 (approximately). That is, we effectively get 20 times as much water heating from 1 gallon of propane as from 1 kwh of electricity.
The cost of my electricity is $0.12 per kwh up to some limit, and then it goes to $0.15 per kwh. So, lets take the higher number, $0.15 per kwh. That means propane would have to cost less than
$0.15 * 20 = $3.00 per gallon
to be cheaper than electric for water heating (and at the $0.12 per kwh, it would have to be less than $2.40 per gallon). I haven't checked propane rates in a while, but it seems that it's at or above $3/gallon right now. In addition, propane water heaters are more expensive than electric. So, electric water heating wins.
Am I missing something here?
I've got an electric 40 gallon water heater and was considering replacing it with a 40 gallon propane water heater. It seems that most people in this area believe propane is a much better way to heat water, but it seems to me that propane will be more expensive.
Here's my calculation.
BTUs
------
per gallon of propane: 91500
per kwh of electricity: 3412
Efficiency ("energy factor")
-------------------------------
40 gallon electric water heater: ranges from 0.9 to 0.95
40 gallon propane water heater: ranges from 0.59 to 0.67
Let's suppose an electric water heater has an efficiency of 0.9 and a comparable propane unit has an efficiency of 0.67 (note that I'm taking the low number for the electric and the high number for propane, which should skew the numbers slightly in favor of propane). Then
"Effective" btus when heating water
------------------------------------------
per gallon of propane: 91500 * 0.67 = 61305
per kwh: 3412 * 0.9 = 3071
The ratio here is 61305 / 3071 = 20 (approximately). That is, we effectively get 20 times as much water heating from 1 gallon of propane as from 1 kwh of electricity.
The cost of my electricity is $0.12 per kwh up to some limit, and then it goes to $0.15 per kwh. So, lets take the higher number, $0.15 per kwh. That means propane would have to cost less than
$0.15 * 20 = $3.00 per gallon
to be cheaper than electric for water heating (and at the $0.12 per kwh, it would have to be less than $2.40 per gallon). I haven't checked propane rates in a while, but it seems that it's at or above $3/gallon right now. In addition, propane water heaters are more expensive than electric. So, electric water heating wins.
Am I missing something here?