<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">see as the temperatures go down & the volume of LP goes down you get less btu/hr. Your furnace is either a 35000 or 40000 unit. </div></BLOCKQUOTE>
Take a look at the explanation below the chart. The purpose of the regulator is to compensate for this. Small cylinders and low temperatures can reduce what is available to regulate, though.
The BTU content of propane is ~93k BTU (91,690 on the linked page, after vaporizing). A furnace rated at 35k or 40k BTU/ hour as noted in the quote would then run about 3 hours for each gallon of liquid propane you have.
Liquid propane is about 4 lb per gallon (a 20lb tank holds 5 gallons, 30 lb tank 7+ -- page says 4.23/gal and 21,591 BTU/lb) That means the furnace will burn a bit more than a pound an hour.
Duty cycle is the big factor. Generally, plan on 50% to maintain 65F temps in 32F wind chill outside. Perhaps 100% at 0F wind chill outside. That means each gallon of propane could last 6 hours in cold temps down to 3 hours worst case.
100 gallon tanks are fairly common for seasonal RV park rentals. That might last 500 hours or 3 weeks in cold temperatures. The typical TT has maybe a tenth of that capacity which means 2 days and that is about right (a bit conservative).
These are very rough estimates so please don't take them out of context or as intended for anything more than providing some clue about how long you might be able to keep warm with a propane furnace in a typical RV.
BTW - one reason household tanks are mounted sideways may have to due to that making for more surface area of the liquid in the tank and that means faster vaporization for more BTU flow. Vaporizing propane at a rapid rate can really cool the tank and even freeze up regulators, too.
|