It depends on what you are using it in.  

A heater buddy, on 5K btu its about four to five hours.  Faster on 10K btu. That's high demand, so high, a common mistake in winter is people to use the high setting and the tank will freeze.  Better to heat your tent, etc. up a little on the 5K before you switch over.  This time of year, we use a Heater Buddy to augment our house heat.  We like it and actually are saving money doing it.  

For a stove and one mantle Coleman lantern, three lasts me an entire weekend.  One basically is a spare, sometimes I use it, sometimes I don't.  Being quite southern, we usually fry and the big demand is a hot pot of perked coffee every morning.  Sometimes, we'll bake biscuits and then we get into our third can.  

Tj

I hear you.  Spending a winter night in my boat or camper is like being in a one bedroom apartment.  Now if I can just figure out a way to get them to the other so far out you gotta double clutch lightening places I go.



On the 1lb can cost.  If you refill them right, liquid not gas, big tank upside down, let gravity fill the little tank, you get bout 16-17 cans depending on how well your refill 20 lb tank guy does.  Average retail on the Coleman cans is about $3:50 these days.  So even accounting for different fills, you save about $2.00.  

You aren't even going to save that if you didn't save the little plastic caps, about one out of four of those open top filled cans is going to leak out. Those little camps provide just enough back pressure to prevent that.  

Now don't skimp on the can refilling by using the one gizmo does it all.  That little tank needs to be below the big tank or it will only gravity feed to a partial fill.  Try it right side up, you are going to go, "Holy Crap, what did I do wrong. This sucks.  It lasts no time"  

If you are at the volume, you are considering refilling cans, I highly recommend going to 20lb tanks and use the hose adapter.  You have to have one anyway if you are refilling cans.  Just know if you buy the rubber one and plan to use it a lot on high volume applications like a 9K btu bigger stove, its best to buy a filter or your'll clog your stove up with the little rubber bits.  Another little hint, don't store you rubber hose in direct sunlight.  That breaks it down.  Two burner cook stove or even the little Heater Buddy, you don't really need the filter.  Just flush your line  if its been sitting a while with gas outdoors.  Blow the crap out before you use it.  

Next little tip, have spare 20lb tanks especially if you are using your grill tank.

Another hint, if you are wanting to use your 20 lb tank indoors use the internal thread hose adapter.  It has more threads than the quick disconnect and holds a tighter seal.  Don't forget to turn the tank off when not in use.  It goes without saying, you smell gas, don't light the damn stove.

Now here's a great tip if you are the rather eat grilled food all year round.  Put your grill on your porch in winter so you can go out and back in.  Heck, when I lived on the Great Lakes, I kept mine on my patio right at my sliding doors.  My neighbors would see a hand come out, a lid open hand twist and turn, lid close, then hand disappear back indoors.  I use to grill 20 below of feet of snow.  

Back on camping, every propane lantern I have is a single mantel.  A double is too much light and typically we all use them turned way down.  The gas to light ratio is the same but those mantels don't go out at the same time.  Though I really like the new Coleman clip mantles, a single mantel its not necessary.  Its not like you are going snag the other mantle that didn't burn out.  

Now you really want some input, get me on small electric room heaters.  I have six of those little buggers all different types and save about $100 to $200 a month in winter with them augmenting my heat pump.  

Tj