Efficient Furnace? April 01, 2025, 09:48:20 am With the future now showing promise of more efficient RV appliances such as the inverter air conditioner, why is it taking so long to come up with a better furnace? Residential furnaces with in excess of 90% efficiency are common. The furnace at our cabin has no noticeable heat from the flue when running, eg, where the one in the LD feels like it heats up the forest more than the interior!Steve
Re: Efficient Furnace? Reply #1 – April 01, 2025, 11:47:43 am Hi Steve; I agree. They should at least have SEER ratings, but of course once built into a motorhome, you are sort of stuck with the footprint. Before LiF batteries I always wanted to put in a thermocouple assembly on the exhaust, so that waste heat could at least ameliorate the power drain from running the heater. Recently I almost had to abbreviate my visit to Jalama Beach. The temperatures were so cold, especially at night. The wind off the ocean at 55 mph one night and moisture laden (not to mention the salt), the heater ran a lot and I nearly ran out of propane. Only 8 gallons in a ten gallon tank. Almost a gallon a night. RonB 1 Likes
Re: Efficient Furnace? Reply #2 – April 01, 2025, 11:54:56 am The exhaust waste is a nod to safety when it comes to combustion appliances and carbon monoxide. It's clearly possible to build more efficient units, but you increase the small odds of having issues that cause occupants to never wake up.In the marine and van industries, diesel heaters are common and chinese knock offs are available. Webasto would be a brand name, and off brands are all over Amazon. Obviously, diesel makes more sense when the engine in the vehicle is also diesel (like many boats, or sprinter vans). It's also easier to engineer a safe combustion system when you have a relatively stable amount of atmospheric O2. Not the case when you change elevations frequently. There are people who have retrofitted these to gas powered RVs (with a small diesel fuel tank). https://www.youtube.com/watch?v=N0X0huHwoSY&t=14sI think it's an issue of fuel type and safety. Many do use a propane catalytic heater (Camco Wave) but wisely (IMO) only use it when they are not sleeping.Rich
Re: Efficient Furnace? Reply #3 – April 01, 2025, 12:17:14 pm Quote from: rich - April 01, 2025, 11:54:56 amThe exhaust waste is a nod to safety when it comes to combustion appliances and carbon monoxide. It's clearly possible to build more efficient units, but you increase the small odds of having issues that cause occupants to never wake up.Sorry, but I don't see how this is true. More efficient combustion does not increase the risk of poisoning. The heat exchanger prevents that.Quote from: rich - April 01, 2025, 11:54:56 amMany do use a propane catalytic heater (Camco Wave) but wisely (IMO) only use it when they are not sleeping.These are external combustion devices, so all combustion products are present in the living area. Any problem with the devices could cause poisoning.Steve
Re: Efficient Furnace? Reply #4 – April 01, 2025, 12:34:15 pm The one motor has a recirculation fan on one side, and a fan to propel exhaust out and draw in fresh air, on the other end. The object is to diffuse the exhaust and dilute it. I was parked once at a confined space campground, where the neighbor's heater exhaust was pointed directly at my side window. I kept the window closed (it was cold) and an eye on the CO monitor's display of below alarm threshold levels. The airtight integrity of any motorhome, is just so-so, even for a Lazy Daze. RonB
Re: Efficient Furnace? Reply #5 – April 01, 2025, 01:02:53 pm High-efficiency home furnaces have large, convoluted heater exchangers with increased surface area, giving the combustion gases more time to transfer heat. A better conventional RV furnace would need to be much larger.If looking for a better furnace, consider the combination water heater/furnace Truma Combi, it's advertises having 90% efficiency. Truma has been building the Combi units for years, and they are seen in European RVs and some domestic Sprinter RVs.Truma Combi eco | TrumaThe Combi has a lower BTU rating but should produce close to the same amount of heat as the furnaces in our LDs, due to its much higher heat recovery. Ron's small propane tank would last longer with a Combi..Another plus would be the extra space freed up by the small Combi replacing both the furnace and water heater.Better appliances are out there.Larry
Re: Efficient Furnace? Reply #6 – April 01, 2025, 04:00:27 pm This heater has been in business in the U.K. for European RV's use. Del City sells units and parts. I didn't see anything about efficiency ratings, probably there somewhere. Whale Heat Air: Lightweight, Powerful Heating Solutions for Your RV - Del... RonB
Re: Efficient Furnace? Reply #7 – April 01, 2025, 04:59:19 pm Quote from: RonB - April 01, 2025, 04:00:27 pmThis heater has been in business in the U.K. for European RV's use. Del City sells units and parts. I didn't see anything about efficiency ratings, probably there somewhere. Whale Heat Air: Lightweight, Powerful Heating Solutions for Your RV - Del... RonBFrom the link I listed above."Truma Combi eco Features:Near-silent operationLightweight and space-saving solutionMaintains constant temperature throughout the RVHighest available energy-efficiency over 90%"Over 90% is as good or better than most modern high-efficiency home furnaces, and it would be quieter too.It sure beats the low efficiency of the Suburban furnaces our LDs have...you will not be able to warm your hands on the exhaust.Larry
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