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cowboyro
Premium Member
join:2000-10-11
CT

cowboyro to pandora

Premium Member

to pandora

Re: Comparing Cost of Propane and electicity heating?

said by pandora:

As a rule of thumb, assume a gallon of propane is about 7 tons, the same quantity of resistive electric heat requires a bit under 25 KWh.

TONS express the heat transfer capacity PER HOUR. As such, you cannot say that it's the equivalent of 25kWh, but the equivalent of 25kW.
You cannot compare power to energy...

PSWired
join:2006-03-26
Annapolis, MD

PSWired

Member

said by cowboyro:

said by pandora:

As a rule of thumb, assume a gallon of propane is about 7 tons, the same quantity of resistive electric heat requires a bit under 25 KWh.

TONS express the heat transfer capacity PER HOUR. As such, you cannot say that it's the equivalent of 25kWh, but the equivalent of 25kW.
You cannot compare power to energy...

Yeah, the units in this thread are all messed up.

POWER (btu/hr, kW, tons of refrigeration, etc.) units express the *rate* of energy delivery. Multiply by time to get the energy consumed.

ENERGY (btu, kWh, therms, etc.) units indicate the total amount of work that can be done, total amount of thermal change, etc. Divide by time to get power.

A particularly egregious error that I see on the forum regularly is using the "unit" kW/hr. A kilowatt is a unit of power. Dividing it by time creates a meaningless quantity. Most times this is used, the writer means kWh, or kilowatt-hour, which is a unit of energy--the amount of energy equivalent to a kilowatt consumed or produced over a one-hour period.

Oh, and while I'm on my pedantic rant, the ton is an especially confusing unit since it was originally derived from the thermal *energy* absorbed by a one ton block of ice. The unit today is used as a power unit corresponding to the refrigeration capacity needed to replace one ton of ice delivery per day.