LP gas furnace at high altitude.
I'm just finishing up building a small, primitive cabin in the Wyoming high country; about 10,100 feet. Originally planning a wood stove, we've tabled that idea for now, after being instructed by an installer that the idea was far more complex and expensive than we'd thought. (8K in venting and likely heavy creosote build up). I'm leaning towards a 20K BTU direct vent propane furnace, but many of them have a 7000 foot altitude restriction. The Martin DV20V is my current favorite and doesn't list an elevation cap, just warns that heating capacity will drop with altitude, which is fine as I sized up the unit. That said, the supplier noted that it should be adjusted for altitude, though the manual doesn't list a procedure for doing this. The manufacturer hemmed and hawed, handed me around the engineering department, then ultimately told me it wouldn't work, though it seemed to me that it wasn't a technical barrier, but perhaps one of liability or simply not being worth the discussion.
I've read here and other places about the challenges of LP in cold climates and high elevations, but also know that the USFS operates a rental cabin very near my place that uses a propane furnace and a very large tank that sits behind it, so it is possible.
I'm hoping someone can help me with general advice in this regards, and answer some of these questions:
- Do most/all furnaces have some way to derate for altitude? Have swappable orifices?
- If I bring my furnace to a local HVAC specialist, can they use tables/WAG-s to derate my regulator/orifices to get to a reasonable level, or would they have to come to the build site to check its burn?
- Due to the cabin's remoteness, 100lb cylinders are as big as I can go, and will be snowmobiled in during the winters. I suspect they'll be subject to more temp and pressure changes than a larger tank, but I'm hoping they'll suffice.
- The model mentioned above has a viewing window where the burner can be observed. Can a visual read of the flame get me in the ballpark of a good burn? Can a purchased or rented combustion analyzer get me the rest of the way?
Thanks for sharing your expertise.
Comments
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Two problems. One is the evaporation rate of the LP gas, which drops with temperature. A lot. A 100 gallon tank may not big enough to get the gas flow needed.
Second is air/fuel ratio. Air at 10,000 feet is a LOT less dense than at lower elevations, and the burner has to be adjusted for that. It may or may not be possible for a given burner to have the correct orifice size — and if the manufacturer hasn't tested it, they're not likely to be of much help for experimentation.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England0 -
Why not check with the Forest Service and ask what kind of furnace they have does it run ok and who services it.
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A burner derates about 4% for every 1000' above 2000'. I imagine in a cabin that will still be enough heat output. So that 20,000 becomes more like 15,000 btu/hr.
A combustion analyzer is the best way to confirm the adjustment. Blue flame is better than yellow.
It's a weird fuel in cold weather, but very common in remote mountain areas. As are wood stoves:)
Many RV have LP heaters with altitude kits available.
Invest in an LP alarm and a CO detector, as you would in a RV. Just for piece of mind.
I think you can pair up multiple `100 gallon tanks, the local LP supplier will know.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Invest in an LP alarm and a CO detector, as you would in a RV. Just for piece of mind.
At least 1 Low Level CO detector. UL listed detectors will not alarm until 70 PPM has been exceeded for up to 4 hours. Low level alert at 15 PPM
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Yes. But I've not had any success getting the Forest Service to return calls.
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Good advice.
The manual states: "Input ratings are shown in BTU per hour and are rated for elevations up to 2,000 feet above sea level. For elevations above 2,000 feet, input ratings should be reduced 4 percent for each 1,000 feet above sea level."
So if I read this correctly, I should derate the furnace by 40%. The installed (LP) orifice from the factory is a 131. I don't suppose that there is a linear size reduction for the orifice though. Any guidance here?
I'm inclined to go with a dual tank set up and give this a try. If I don't, the near term solution is to run cheap diesel heater on a deep cycle battery to get me through this winter, then try something different in the spring.
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Are you totally against Colorado Anthracite Coal in a console heater or using a simple oil burner furnace with a top fed oil tank for the oil line using a small 110 volt gasoline generator that you can take back down the mountain when you leave??
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Some info here.
And here.
How big is the cabin? I have the smallest one of these in my truck camper, super simple to install with their double wall flue pipe.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
The cabin is just under 200 square feet, 16x12 exterior dimensions, but has a very tall steep roof and a loft. R19 insulation all around, including under the floor.
The problem with the wood stove, I'm told, is fourfold. We'll be burning soft wood, at high altitude, through a long flue (more than 20') in very cold temperatures, all of which lead to creosote build up. There may be another small cabin build in the future, and I plan to make wood work for that one, but the snow is already accumulating where this 80% finished cabin is, and I need a near term solution to get it warm enough to finish the interior and use it. Until late June all materials will be brought in by ski or snowmobile, so another point against heavy and bulky wood stoves and their venting. I like that stove you put in your camper, and had seen it while researching for my own cabin. Ultimately I was leaning towards the Hearthstone Lincoln for its ability to burn long, low and clean. Next cabin.
I think, or at least hope, that a dual tank setup will be enough for at least a low burn setting on the propane furnace. Of course if it's not it'll be on a bitter cold night that we find out. Better have lots of emergency blankets. Another challenge with LP is this furnace vents directly outside, but I'll need to raise the vent above the snow, or at least dig the snow well away before we use it. This area gets in excess of 10' of snow, and often more than 15'.
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then LP fired heaters. It construction. 50+* is fine.
Please invest in “LowLevel” CO detectors.
FWIW. We lived in Leadville Colorado 10,000 elevation. Not an issue.0 -
I'm not sure what the benefits of coal are, perhaps no creosote build up? The setup sounds a bit complex. Though I don't mind that complexity, we hope to make this cabin available to family and friends, and maybe even rent it to winter sports enthusiasts, and so many moving parts would be a no-go.
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It is not complex stove to use and operate, you have to install it properly and use a chimney cap to keep the snow out of it.
No creosote, plenty of heat, long periods between loading a top fed coal stove. Your cabin is smaller than a caboose and a pot bellied stove using coal would heat it with no issues as long as you tend it properly.
A caboose oil drip stove would be more problematic.
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50+ what? Yes, I will absolutely run at least one low level CO detector. Good to hear that you had good results burning LP at that altitude.
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50 + Degrees F!
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Great little book has orifice sizes (pg 52) vaporization rates etc
Found this online. Great little book with lots of propane info. I have had this for 40 years but never did much propane.
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Lp is a common fuel in the high, remote mountains. I worked at Snowbird ski resort 8100- 11,000’ elevation, back when all the buildings were 100.% lp fired. So high altitude snd cold conditions. Large Sellers firetube boilers in each building in addition to all the restaurants equipment .
Occasionally in very cold conditions we would run vaporizers to warm the LP. So in fact LP does still function as a fuel in cold conditions.
The vaporization tables answer your questions. Dual tanks get them filled at the beginning of the season
How long they will last depends on how much fuel you use.
You can add gauges or watch the frost levels on the tanks to know when to top them off. With a low firing rate, you may be fine
Ill bet the local LP delivery and service people will also have a good idea of what works in the area.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Super useful!! Thanks.
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