RV LP Furnace Efficiency?

ktmrfs wrote:

S Davis wrote:

ktmrfs wrote:

JaxDad wrote:

beemerphile1 wrote:

sidney wrote:
...Anyone have the real world efficiency rating of the typical RV LP furnace. I'm guessing 70 to 75%....

Why guess? Do the math. Look at the label on YOUR furnace. Divide the output BTU by the input BTU.

That only gives you the combustion efficiency, it does not account for the heat exchangers efficiency.

A typical RV furnace is only ~70% efficient.

I disagree. stated BTU output on a furnace is the BTU output through the heat exchanger. E.G. the BTU of the air coming out of the heat exchanger. BTU input is the BTU of propane or NG going into the burner.

combustion efficiency on a gas furnace is very close to 100%, like most any external combustion vapor fueled appliance.

Well not exactly, when figuring combustion efficiency you have to factor in everything that supports combustion in that appliance. Including heat of exhaust gas. If anyone is close to Mount Vernon WA I have a combustion analyzer I can test your furnace with and give you exact numbers.

If one looks at the BTU of the input gas source and then measures the TOTAL BTU output after combustion, it will be very near 100% for a properly adjust external combustion source. That calculation will include the BTU in the heated exhaust gas and the heat of vaporization of the water as a byproduct of combustion as well as the heat going into the heat exchanger. Basic thermodynamics.

Now, when one looks at the heating efficiency, the input BTU of the fuel and the BTU of the heating output, that's another story, usually well under 100%. 95% for a condensing furnace.

But we are talking about the combustion efficiency of a furnace not a open flame, so you need to account for the loss out the flue and any other losses not going into the conditioned space to figure efficiency.