There's no good answer to that.  A few nights... a few months.  Somewhere in between usually.  If you have shore power, use a $20 electric heater from some place like Walmart though.

TT

If you are using the furnace in sub-freezing temperatures and running the refrigerator and running the stove and water heater (as needed), you may only get a couple of days out of a tank. If you are just running the refrigerator and occasionally the stove, a tank will last months. Reality is that your use does determine how long a tank will last.

Easy way to determine fuel level if your tank does not have a gauge is to heat some water and pour it over the tank. Wait a second or two and feel the tank, starting at the top. It will be warm at the top. When you get to where the liquid level is, it will be cold. You may actually be able to see the liquid level line. Or, you could purchase a stick on gauge so you don't have to feel it although you will still need to use hot water to activate the change to see the level. You could also purchase a gauge that either weighs the tank or reads through the tank wall to determine the level. It depends on how much you would want to spend. The hot water and feel the tank method is pretty cheap.

Another option my be to have a second 20# filled tank for a spare.  We normally camp in the shoulder months April-May and September-November when the temps are often cool and the furnace gets a real workout since we normally boondock, no electric available - as in our national parks.  Last year while in RMNP the night temps often were in the 40's, propane was also used for  HW and fridge. 

The tank was nearly full when we started the trip but on the way home, the tank had to be exchanged, so in that case we got 8 days out of the tank, but that was with pretty heavy usage.  None used during the day, turned furnace off while hiking.  Also, always try to fill at a hardware store or similar where they will FILL your tank.  Avoid going to gas stations where they offer Blue Rhino or similar where you pay a whole lot more to get a tank that is only 75% full.  Two days ago I filled my empty 20# tank that was empty for $ 14.50 at the neighborhood hardware store.

OldNeumanntapr, who told you that? BBQ tanks and the tanks you buy from an RV dealer are the same, ie,, meet the same specifications. The only difference is the RV dealer's markup.... 

The admonition against swapping tanks seems too harsh to me.  Yes, it's probably a little more expensive than going someplace that will fill them, although the price difference isn't always that great.  Do whatever works for you and suits your convenience.  Just don't eat at restaurants when you're on the road.  Why would you?!  They charge way more than it would cost you to fix a meal in the Pod and you can eat as much as you want when you fix the food!

Yeah, and I never heard of a difference between BBQ tanks and RV tanks either.  I've never seen a label indicating a tank was one or the other.  This is new to me.

TT

"Motorhomes, though, have installed ASME (American Society of Mechanical Engineers) tanks, not DOT tanks.  ASME tanks are not required to be re-certified since they are permanently installed. But DOT/TC cylinders, both vertical and horizontal, because they can be removed, transported and filled independently, do qualify for periodic re-certification. Allpropane containers, tanks and cylinders, however, should be periodically inspected, cleaned and tested for leaks. All of which should be considered preventive maintenance common sense."

So, if you have a class A motorhome with a permanently installed propane tank, that is qualified under ASME standards. But our 20lb cylinders are qualified under DOT regs, and BBQ ones are the same, because they all wind up getting removed from their mountings and transported on the roads one way or the other. 

The recertification period is perhaps another reason to exchange tanks once in awhile. If you buy a new cylinder and hang onto it for 10 years you'll have to get it recertified, but if you exchange that should end up being Blue Rhino's (or another supplier's) problem. If I were to hang onto a cylinder here in the OBX for 10 years it would be a pile of uncertifiable rust...

The only RV propane tanks I could find on the interweb are configured for permanent installation on an RV.  20 and 30 pound tanks are listed for RV or BBQ use.  Please show me the difference and where to get the RV tank.  If there is a difference I want the proper one.

I get the tanks re-filled at one of a few gas stations around here that offer the service.Works great; you pay just for the propane, and you get a full tank.

However, all 20 lb propane tanks that I've ever seen have an expiration date. When that date comes rolling around, I will swap it for a new tank. To date, I've either gotten Blue Rhino or Suburban, and ALL of the exchange tanks I've gotten were in like new condition without exception. Occasionally they are not completely full, but they've all been in excellent condition.

The exchange places are different from the fill places around here. Exchange places that we have are hardware stores and grocery stores.

But, if there really is a different spec'd tank I could get that was more robust for RV use I would certainly reconsider. 

https://portal.phmsa.dot.gov/rinlocator

If anyone is interested, the standard for RV safety construction is NFPA 1192. You can view it online for free on the NFPA website if you register. This standard has all the requirements for types, mounting, clearances, ventilation, access, regulators, plumbing, etc for propane cylinders on RV's. I'd recommend that anyone considering changing from the standard tongue mount (or mounting heat producing things like generators near the propane cylinders) read this first. 

Kind of gratuitous at this point, but in decades of dealing with propane tanks, mostly, but far from exclusively, 20 lb tanks, I have have never heard of 20 lb RV tanks versus 20 lb BBQ tanks.  Buying tanks, exchanging them, refilling them, no one has ever said, "Oh, you have a BBQ tank." or, "Do you want to swap for an RV tank?"  This thread is the first I've ever heard of this.  (So I don't think there are two different things.  Other than the permanent tanks on board some motor homes.)

I've never had to, or cared to, deal with re-certifying a 20 lb tank, but I've heard that if/when you go through the process the re-certification is only good for 5 years after which it can't be re-re-certified.  Don't know if that's true.  Not sure anyone would want a 17 year old tank anyway.  In most cases, long before it gets to that point, the highest value of the old tank would be to use it as a swap-out for a newer tank.  My opinion, of course.

TT

This post caused the "drift" so apparently not everyone knew the facts on this like you Mcarter.