Furnace output, efficiency...

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Furnace output, efficiency...

March 23, 2021, 07:13:15 pm

While housecleaning, I happened to notice tags on the Suburban furnace in our rig:
input: 19000 Btu/hr
output:14400 Btu/hr
claimed thermal efficiency: 75% (actually almost 76%)

So, this is a rough figure for those investigating higher efficiency heating options. A Wave 3 may be about 95% efficient, but the furnace puts out 5 times the rate of heat. But, furnaces should be able to do better - a modern residential furnace is also capable of 95% efficiency.

Steve

Re: Furnace output, efficiency...

Reply #1 – March 23, 2021, 07:20:43 pm

I know there are many variables here but I’m wondering if a Wave 3 is sufficient for a 27’ model?

Re: Furnace output, efficiency...

Reply #2 – March 23, 2021, 07:43:22 pm

"I’m wondering if a Wave 3 is sufficient for a 27’ model?"

If the question you're asking is "is it sufficient as the sole heart source?", then for most parts of the US, I'd say "no." As Steve pointed out, the standard furnace in a 26.5' Lazy Daze puts out about five times as much heat as a Wave 3, and thanks to its blower, does a much better job of spreading that heat around. A Wave 3, like any radiant heater, basically just heats what it's pointed at.

If you're asking "Is it sufficient as an auxiliary heat source?", then the answer is "Maybe"... depending upon whether heating a small area is sufficient. For example, in my current rig (19' Airstream), I have a Wave 3 mounted four feet from the office chair where I sit most of the time (see photo). In the mild climate of western Arizona, that works just great, and I rarely used the furnace this past winter. But if I were spending most of my time elsewhere in the rig, it wouldn't be so great, because radiant heaters aren't good at spreading heat around.

In other words, if you spend most of your time in one place in your rig, and if you can find a way to put a Wave 3 a few feet from that area (either wall-mounted or on legs with a hose), you'll probably be happy with it. If not, you may want two.

You could also go for a Wave 6, as some of our members have done, but it's been my experience that two small heaters do a much better job of heating an RV evenly than one large heater. Note that Larry has two Wave 3's, located at either end of his 23.5' Front Lounge.

Re: Furnace output, efficiency...

Reply #3 – March 23, 2021, 07:55:11 pm

Quote from: HiLola - March 23, 2021, 07:20:43 pm

I know there are many variables here but I’m wondering if a Wave 3 is sufficient for a 27’ model?

A Wave 3 is not going to keep the entire interior warm, only a part of it. Many find the Wave 6 to be too powerful and hard to stay far enough from its infrared heat.
We use the furnace to take the chill off and the Wave 3 for long-term heat. When winter camping, often the Wave 3 is turned on in the late afternoon before it gets too cold. It's very pleasant to come back to a warm rig after an hour or two around a campfire.
In very cold weather, it's left on all day while we are gone. It's better to come back to a 65-degree interior, compared to one in the low 40's or colder. It takes a long time to fully warm up a cold interior.

Larry

Re: Furnace output, efficiency...

Reply #4 – March 23, 2021, 09:16:32 pm

Good info, thanks! For a two heater setup, can you tee off the same propane line?

Re: Furnace output, efficiency...

Reply #5 – March 23, 2021, 10:38:39 pm

A few months ago I was toying with the idea of a rig designed with in-floor radiant heating and a single boiler replacing the heater and water heater. Given the high efficiencies of current boilers, it sounded interesting. So, I did a heat need calculation. I used the types and thicknesses of insulation in my rig, the interior volume, surface area, and window area and type. Having been in some really extreme conditions, I used an exterior temperature of -5 and an interior temp of 70. Crunching the numbers, I came up with a demand of 14,000 BTU's. I was astonished at how closely this matched the capacity of the furnace.

I then did the calcs to size the heating field for a radiant system. Tubing cannot be placed under cabinets, closets, and so on. Not much floor area is left. Second, fluid temps must be kept fairly low, lest the plywood in the flooring heats to the point where it might warp, distort and delaminate. A floor radiant system would only yield a small percentage of the needed BTU's. It was not even close to what would be needed.

It was an "Oh Well moment for me. As to Steve's question about a Wave 3 being enough by itself, using his number of it being 1/5 the capacity of the furnace, it might be ok on a mild night, but I doubt it would get the job done in really cold weather.

How cold is cold? I looked at a temperature differential of 75 degrees and the heater could handle it. If a Wave 3 can produce 1/5 the amount of the furnace, a VERY crude estimate would be that the Wave 3 could handle 1/5 of a 75 degree difference, or about 15 degrees. If you want to keep the inside at 70, then a 55 degree night is the limit. If you are ok with a 60 degree interior, then something in the neighborhood of 45 degrees would be the limit.

I emphasize that this is a very crude approximation. The actual numbers would depend on your floor plan, interior volume, windows, floor, walls and ceiling area and insulation. The calculation is somewhat lengthy, and I am not about to repeat it, but this may give a sense of what a Wave 3 can do for you. (And it is a decent match for what Larry and Andy said.)

Ken F in NM

Re: Furnace output, efficiency...

Reply #6 – March 24, 2021, 01:11:04 am

Ken, we too also considered the in-floor hydronic heat option for our 98~MB but because of lack of floor space to interior space you would have to run the installed furnace for heat but you would have warm floors. You could add radiators with blowers to supplement the floor heat from your boiler to make up for the lack of floor space but the whole project would be expensive. We recently may have missed an opportunity to add 120v under laminate floor heated mats when we removed our carpet to add vinyl laminate. We had tossed the microwave so we have the extra 20amp circuit, so heated floors might have been nice when plugged in. I think that the in-floor electric heating mats are probably to hot for vinyl laminate flooring.

Karen~Liam
98 ~ MB
NinA

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