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.

[BFL13]

time2roll wrote:
I just want to warm some coolant and move the waste heat to the battery.
Have to modify the connecting tailpiece to have some coolant absorb the heat and then pump to the battery.

Interesting approach. The exhaust is intermittent, so storing the heat in the "coolant" would address that, but you also then have two transfers instead of one. Hmmmm.

I would have the battery bank in a "little red wagon" to get it closer to the furnace exhaust, but there are all sorts of ways to do this if you were more of a full timer in one spot long enough to make it worth the bother.

I agree the furnace noise is the greater problem. Hate it when the furnace comes on and you can't hear the TV/DVD.

[time2roll]

I just want to warm some coolant and move the waste heat to the battery.
Have to modify the connecting tailpiece to have some coolant absorb the heat and then pump to the battery.

[DrewE]

ktmrfs wrote:

I agree with Dusty. The other thing to think about is how often or long the typical RV furnace is run. We travel a lot, 3 months/year is common. I doubt I use more than $50 of propane each year for heat. Increasing the efficiency of an RV furnace from 60 percent to 90 percent wouldn't make much of a dent in my propane cost, so the extra cost of the furnace would need to be minimal.

In reality I would easily pay more for a quieter furnace, way more likely to do that than pay more for a higher efficiency furnace.

That is a good point. I suspect also that many RV furnace users would care quite a bit more about improvements to DC power usage than to propane usage; getting an extra night of heating out of a battery bank charge is often of more value than needing to refill the propane a little less frequently. More energy efficient blowers are certainly well within the reach of current technology, though often at the expense of space required.

[Boon_Docker]

Sorry to rain on your parade, but there are gravity furnaces (non forced air ducting) and forced air combustion furnaces (residential) and forced draught (RV).

[RLS7201]

dougrainer wrote:

Dusty R wrote:
I believe that RV furnaces could be made more efficient and not cost a lot more to manufacture.
I'm an old school part time furnace guy.
Haven't done much furnace work in the past 15 years.

Dusty

Whenever I see someone post something like this, I wonder. WHY do you not do that. You will be a millionaire in no time. There is a BIG difference between the design of a RV furnace and a HOME furnace. There are space considerations you have in an RV that you do not usually have in a Home system. Doug

I'm with you Doug. Those day dreamers can't even speak the language of heat exchangers. IE gravity, induced exhaust, forced air combustion, etc.

Richard

[ktmrfs]

Dusty R wrote:

dougrainer wrote:

Dusty R wrote:
I believe that RV furnaces could be made more efficient and not cost a lot more to manufacture.
I'm an old school part time furnace guy.
Haven't done much furnace work in the past 15 years.

Dusty

Whenever I see someone post something like this, I wonder. WHY do you not do that. You will be a millionaire in no time. There is a BIG difference between the design of a RV furnace and a HOME furnace. There are space considerations you have in an RV that you do not usually have in a Home system. Doug

I under stand what you are saying, but the majority of owner's only look at the cost of things, not at how much it cost to operate.
Williamson furnaces were one of the best and efficient home furnace. Many home owners recognized that and used them even though they cost more. But Williamson went belly up.
The reason that we have the high efficient home furnace today is because our government demanded it.

I'm not an engineer, and I'm not sure about all the safety requirements, and I'm not sure I could find all the parts I would need.
I have many other things to do, but if I had a good working RV furnace to play with perhaps I would give it a try.
But would it sell well enough to produce? I doubt it sell well, as it would cost more.

Dusty

I agree with Dusty. The other thing to think about is how often or long the typical RV furnace is run. We travel a lot, 3 months/year is common. I doubt I use more than $50 of propane each year for heat. Increasing the efficiency of an RV furnace from 60 percent to 90 percent wouldn't make much of a dent in my propane cost, so the extra cost of the furnace would need to be minimal.


In reality I would easily pay more for a quieter furnace, way more likely to do that than pay more for a higher efficiency furnace.

[Dusty_R]

dougrainer wrote:

Dusty R wrote:
I believe that RV furnaces could be made more efficient and not cost a lot more to manufacture.
I'm an old school part time furnace guy.
Haven't done much furnace work in the past 15 years.

Dusty

Whenever I see someone post something like this, I wonder. WHY do you not do that. You will be a millionaire in no time. There is a BIG difference between the design of a RV furnace and a HOME furnace. There are space considerations you have in an RV that you do not usually have in a Home system. Doug

I under stand what you are saying, but the majority of owner's only look at the cost of things, not at how much it cost to operate.
Williamson furnaces were one of the best and efficient home furnace. Many home owners recognized that and used them even though they cost more. But Williamson went belly up.
The reason that we have the high efficient home furnace today is because our government demanded it.

I'm not an engineer, and I'm not sure about all the safety requirements, and I'm not sure I could find all the parts I would need.
I have many other things to do, but if I had a good working RV furnace to play with perhaps I would give it a try.
But would it sell well enough to produce? I doubt it sell well, as it would cost more.

Dusty

[ktmrfs]

Sam Spade wrote:

ktmrfs wrote:

my sticks and bricks 15 year old gas furnace has a blower for the combustion air on the flue exhaust side. In fact, likely on almost any gas furnace anymore.

I'm sorry, I forgot about "high efficiency" gas furnaces, which have PVC plastic "chimneys" because the exhaust temperature is so low.

I have no information on whether or not that applies to "almost all" of them these days though.

And I had no idea that a "low end" trailer or RV would have that kind of arrangement. I stand corrected.
(I still haven't looked at mine.)

mine isn't even high efficiency, it is 80 percent, the lowest efficiency that is allowed but still has the fan. Same with my folks hot water (not steam) heat boiler which has ane exhaust fan.

[BFL13]

I always wanted to use that heat coming out the side of the trailer to keep the battery bank warm (which makes for more AH) but I never got around to it. Don't stay camping long enough at a time in the winter to make it worth the bother.

One thing is you are not supposed to restrict the outflow, so you would have to be careful about trunking ideas. Then you don't want that nasty stuff getting back into the trailer somehow if the battery bank is inside like in a 5er.

If you were in one spot long enough to make the bother worthwhile, you could maybe move your battery bank to a better location and rig some sort of trunking to go by them.

An evil RV god figured out that when it is cold the furnace is on more AND the batteries don't have as many AH either. Double whammy.

[dougrainer]

Dusty R wrote:
I believe that RV furnaces could be made more efficient and not cost a lot more to manufacture.
I'm an old school part time furnace guy.
Haven't done much furnace work in the past 15 years.

Dusty

Whenever I see someone post something like this, I wonder. WHY do you not do that. You will be a millionaire in no time. There is a BIG difference between the design of a RV furnace and a HOME furnace. There are space considerations you have in an RV that you do not usually have in a Home system. Doug

[Dusty_R]

I believe that RV furnaces could be made more efficient and not cost a lot more to manufacture.
I'm an old school part time furnace guy.
Haven't done much furnace work in the past 15 years.

Dusty

[Dave_H_M]

:S are we in the ozone layer or what? :h

[Sam_Spade]

JaxDad wrote:

Gravity? I suspect you meant to say convection.

There is no convection without gravity.

[Dutch_12078]

JaxDad wrote:

Sam Spade wrote:
I've dealt with a LOT of gas furnaces over the years, both in permanent structures and house trailers and have NEVER seen one where the combustion air was not gravity fed.

Maybe I will learn something new today. 🙂

Gravity? I suspect you meant to say convection.

Either way, I'm not sure how well a foot tall mostly horizontal furnace would vent when the intake and exhaust are at basically the same height.

There kind of needs to be some appreciable height for the hot air to rise to create enough vacuum / air flow for cold air to be drawn in. If the 'intake' and 'exhaust' were at the same height the heat would just spread equally between them, assuming both ports were equal size.

There isn't a lot of height difference between the inlet and outlet on an RV water heater, but convection works quite well there. I do agree that the even smaller available space in an RV furnace would be a problem though, without the fan to insure exhaust circulation.