Hi,Running our Suburban propane furnace it seems like the unit is pushing as much (or more) heat out of it's exterior vent as it is to the interior vents. At the vents the flow is a gentle convection of warm/hot air. Standing outside it's like a hair dryer on low. It consumes a large tank of propane pretty rapidly .. one or two days with temps in the thirties and thermostat set to ~62This can't be normal .. can it? I'm interested to hear the experience of other cool weather campers before I take it to a shop for what might be an expensive fishing expedition.

You will get roughly 1/3 of the output out the exhaust (a 30k btu/hr unit loses around 10k btu/hr out exhaust)- unless you want a closet sized furnace, that's about as good as it gets. Not to say you shouldn't inspect the ductwork inside.

That, and RV's are drafty and poorly insulated. Saw a Class C in Canada that had 3 or 4 of the big 100-pound cylinders mounted across the back. I take it they winter camped in the thing.

That heat outside is the exhaust from the combustion process AFTER it has flowed thru the heat exchanger that warms up the room air for inside heat.RV furnaces are roughly 65% efficient in the transfer of heated combustion air to heated room airWhen you think about it.....not bad for a 9" X 17" X 20" Box that has an air flow of 350 cfm or less and a propane system pressure of 0.4 psi

Does the propane burner ever cycle during the heating process?This would indicate low interior airflow and the firebox running too hot.Fairly common actually.Otherwise yes a lot of carbon monoxide filled heat goes outside.

IWally wrote:At the vents the flow is a gentle convection of warm/hot air. This can't be normal .. can it? The heat going outside probable is normal. ALL vented heaters/furnaces work that way to some degree.The "gentle" flow of heat inside, however, probably is NOT normal and may mean that your fan has failed.

Propane furnace sending heat to outside vent | Good Sam Community

58 Replies

Chris_Bryant
Explorer II
Dec 15, 2016
IWally wrote:
Thanks everyone for your helpful explanations!

Sam Spade wrote:

The heat going outside probable is normal. ALL vented heaters/furnaces work that way to some degree.

The "gentle" flow of heat inside, however, probably is NOT normal and may mean that your fan has failed.

@Sam .. I think you might be onto to something. It may be that a difference between forced air at the exterior vent and UN-forced air inside makes it more noticeable.

Merry Christmas!

They are both the same motor- one cannot fail without both failing, plus the sail switch is specifically meant to prevent this.
2oldman
Explorer II
Dec 15, 2016
It's also venting moisture.
IWally
Explorer
Dec 15, 2016
Thanks everyone for your helpful explanations!

Sam Spade wrote:

The heat going outside probable is normal. ALL vented heaters/furnaces work that way to some degree.

The "gentle" flow of heat inside, however, probably is NOT normal and may mean that your fan has failed.

@Sam .. I think you might be onto to something. It may be that a difference between forced air at the exterior vent and UN-forced air inside makes it more noticeable.

Merry Christmas!
Sam_Spade
Explorer
Dec 15, 2016
IWally wrote:
At the vents the flow is a gentle convection of warm/hot air.

This can't be normal .. can it?

The heat going outside probable is normal. ALL vented heaters/furnaces work that way to some degree.

The "gentle" flow of heat inside, however, probably is NOT normal and may mean that your fan has failed.
time2roll
Nomad
Dec 15, 2016
Does the propane burner ever cycle during the heating process?
This would indicate low interior airflow and the firebox running too hot.
Fairly common actually.

Otherwise yes a lot of carbon monoxide filled heat goes outside.
Old-Biscuit
Explorer III
Dec 15, 2016
That heat outside is the exhaust from the combustion process AFTER it has flowed thru the heat exchanger that warms up the room air for inside heat.

RV furnaces are roughly 65% efficient in the transfer of heated combustion air to heated room air

When you think about it.....not bad for a 9" X 17" X 20" Box that has an air flow of 350 cfm or less and a propane system pressure of 0.4 psi
j-d
Explorer II
Dec 15, 2016
That, and RV's are drafty and poorly insulated. Saw a Class C in Canada that had 3 or 4 of the big 100-pound cylinders mounted across the back. I take it they winter camped in the thing.
Chris_Bryant
Explorer II
Dec 15, 2016
You will get roughly 1/3 of the output out the exhaust (a 30k btu/hr unit loses around 10k btu/hr out exhaust)- unless you want a closet sized furnace, that's about as good as it gets. Not to say you shouldn't inspect the ductwork inside.

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Propane furnace sending heat to outside vent

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