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Old 11-20-2022, 11:02 PM   #1
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RV Furnace Efficiency Ratings?

I do not see where RV furnaces are rated for LPG efficiency (heat into house vs heat wasted out the flue). I find plenty of discussion of electrical consumption, but thatís not what Iím looking for.

One thing I did find was that the btu ratings for RV furnaces refer to the btus of input to the furnace; no mention of output. The difficulty in finding ratings that are universally available for residential furnaces makes me suspect they might be pretty low, maybe even lower than residential builderís grade 80% efficient furnaces.

Anybody know?
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Old 11-21-2022, 08:20 AM   #2
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Heater efficincy could be determined by calculation with a lot of analytical measurement tools.........requires fuel BTU content, fuel consumption rate, flue gas temperature and oxygen content, outside air temperature and inside supply and return air temperatures. Maybe an rv heater manufacturer has done that.
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Old 11-21-2022, 08:32 AM   #3
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My experience is that an rv furnace is near the 10% efficiency rating. All that I have had usually have more heat going out the exhaust than the inside. Just my opinion so take it for what you paid for it.
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Old 11-21-2022, 09:00 AM   #4
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I'm not sure I would buy 10%, but I would be extremely surprised if it was above 50%. "David 70" is right on about the energy wastefulness of RV furnaces. I do think that considerably more heat comes out the exhaust than comes out of the inside registers, combined. My guess would be in the 30% range. So I'll split with David and guess 30%. Pretty sure that's why they don't post the numbers anywhere. It would scare too many people!!! I've wondered the same thing, actually. Same goes for the water heaters. Higher end new water heaters and furnaces for homes have PVC exhaust paths, so you know they put the bulk of the energy where it is needed, and not "up the stack".
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Old 11-22-2022, 07:50 AM   #5
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Thanks for the replies. I suspected the fuel efficiency might be bad, but you all have opened my eyes! If I think of it Iíll call suburban.

Thinking about residential central AC units, Iíve noticed that as minimum SEERs allowed to be sold have risen over the decades the units have gotten bigger and BIGGER, and more and more expensive $$$. Since RV mfrs. presumably want 1) low price and 2) small size, those two factors might be the primary reasons for low efficiency. Without a sticker to inform consumers of energy use that leaves no one to push for greater efficiency. Now that I think about it they might be right to do that. I kept my last travel trailer for ten years and camped a lot. Between its very tight construction, always having an electricity hookup, using electric heaters almost all the time and having all plumbing and the water tank inside, I only used two bottles of propane in ten years!
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Old 11-22-2022, 07:59 AM   #6
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70% per https://campergrid.com/rv-furnace-wa...0the%20furnace. Suggest checking with the specific furnace manufacturer and model
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Old 11-22-2022, 10:28 AM   #7
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Thank you for that link, CAMP CA. I noted that the article said furnace efficiency was a maximum of 70%. Not great, but not at least we get more heat into the RV than goes out the flue.


I called Suburban and they don't talk to customers. All their telephone choices led me to a woman who said call a dealer. I've emailed United RV in Fort Worth, TX who sell one of the furnaces in my RV. We'll see.
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Old 11-30-2022, 10:25 PM   #8
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Looks like at least some Suburban furnaces have the input and output listed on a label.

Attached one is 80% efficient.
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Old 11-30-2022, 11:43 PM   #9
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I've worked on these furnaces for years. I have found the biggest problem to be that the ducting that comes off the plenum is very poorly sealed if at all. If you pull out the furnace core and have a look in side the core frame (plenum). often I find the duct plugs just rattle around in steel case leaking huge amounts of air. They need to be sealed with aluminum tape from the inside to get more "heated" air to the duct system. the rear panel leaks just as bad and has only 4 screws holding it on. Seal the duct outlets from the inside and the air flow to the ducting system will increase. Just replaced the main board, it lasted 21 years. the motor on the other hand lasts only about 10 years if that. The main bearings go out and the motor has to be replaced. The motors are very over priced at $200. range.

These furnaces could be much higher in efficiency if the plenums were insulated and a intake air filter were installed. On my sf-42 there is just one, 1/2" screw that holds the furnace core in the plenum. then the gas line, 4 wires and the furnace core comes right out. because there is no filter it is always dusty and must be blown out. Mine was originally installed with wire nuts that tend to loosen up due to vibration of the coach. Installing blade connectors makes it even faster to remove for cleaning and such.

There are many changes that can be cheaply made to increase the efficiency of these furnaces, but who expected folks to live full time in them???
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Old 12-01-2022, 06:58 AM   #10
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I’m not sure that the “wasted” heat coming out the exhaust is much different than regular propane or nat gas furnaces for home use. I do know you don’t want that exhaust coming into your RV.
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Old 12-01-2022, 12:09 PM   #11
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I canít imagine the efficiency of the furnace matters to 99 44/100ths of RV buyers. The next buyer who tells the dealer I would have bought that quarter of a million dollar rig if the furnace had a seer rating of 24 instead of 22 will be the first.
Fact is RVs are less than 400 square feet, often much less. The ceilings are lower than the average house and they are chock full of furniture, cabinets and appliances. There just isnít much footage to actually heat or cool. Actual efficiency does not matter to the overwhelming percentage of buyers. At most they only care if the things will heat and cool the rig to a comfortable temperature.
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Old 12-01-2022, 12:23 PM   #12
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Ceaser is right, but that should not stop the DIY'rs from putzing around and trying to improve the efficiency of our heating, cooling, water, sewer systems.
Sometimes a few screws, some high temp tape and a bit of caulking will do wonders for your coach. And just think how proud the DW will be of you, that you cared enough to make her more comfortable. Mine however EXPECTS that.

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Old 12-01-2022, 12:35 PM   #13
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I agree that furnace efficiency isn't much of a factor in an RV purchase, but when you get your first big surprise $350 charge for one month's propane to heat your coach in a southern Idaho winter, trust me, IT MATTERS!

Unfortunately, a furnace change-out probably isn't in the cards as a viable solution. Creative insulation, alternative energy options and adjustment of habits become very important, however!
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Old 12-01-2022, 12:36 PM   #14
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Quote:
Originally Posted by Love2Pack View Post
I do not see where RV furnaces are rated for LPG efficiency (heat into house vs heat wasted out the flue). I find plenty of discussion of electrical consumption, but that’s not what I’m looking for.

One thing I did find was that the btu ratings for RV furnaces refer to the btus of input to the furnace; no mention of output. The difficulty in finding ratings that are universally available for residential furnaces makes me suspect they might be pretty low, maybe even lower than residential builder’s grade 80% efficient furnaces.

Anybody know?

My older Atwood 8531-IV is rated at 30,000 BTU input, and 24,000 BTU output, it's printed right on the blower housing. A little math and that calculates to 80% efficiency. That's a 20 year old heater, and the new ones are supposed to be quieter and more efficient.
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