Propane furnace sending heat to outside vent

[IWally]

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 ~62

This 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.

[MrWizard]

The gas or oil fired furnace in your stick house, does the same thing
It's just not as noticeable since that heat goes up the chimney flue , not out the side wall

[IWally]

More great responses - thanks!

I knew/know just enough (very very little) about these things to suspect that there is an automatic kill ('sail'?) switch but thought it might work as long as the exterior blower worked .. if in fact there were two fans. It seems plausible that it's just one fan working hard to push air to the larger interior vents.

Is it normal to go through a 30lb tank in one day?

[Boon_Docker]

The exhaust vent air will always feel hotter than the interior vent air. The reason is the furnace is pushing a lot of air out a small opening (exhaust vent). On the interior the furnace is pushing a lot of air out, but through a very large opening. Thus the interior air feels much cooler than the 65 percent efficiency rate.

[nineoaks2004]

To answer the question, it is normal...Look on the outside vent cover and it says "HOT"

[Boon_Docker]

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!

If the fan has failed the sail switch would not operate properly and the furnace would shut down.

[Boon_Docker]

Deleted Double Post

[Chris_Bryant]

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]

It's also venting moisture.

[IWally]

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]

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]

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]

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]

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]

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.