Propane heater questions

[Gazz]

A few weeks I bought a propane heater at an estate sale. It's the torpedo style that claims 85,000 BTUs. After replacing the thermocouple it runs great and warms the shop quickly enough but sucks so much propane from the 20 lb bottle that the bottle freezes and the heater goes out. I know the bottles can be placed in a pan of water to fix this but it seems like a less than workable solution considering the freezing temps here in the north east that I need to run it in. I had the same problem with my gas forge but solved that by a manifold connecting two bottles together and I would like to avoid this option for the heater given its portable nature. Would I have the same problem with 100lb bottles? The bottles would be stored outside in this case. Or do I need to get some kind of electric tank or bottle heater?

[chipmaker4130]

Larger bottles will help a lot. When you say 'stored outside', does that mean they'll be out there while in use? In a cold climate that makes things really difficult. You can also gang together multiple 20lb bottles and get the same effect as using a larger one.

[Gazz]

Thanks for the response! Yes, a 100lb bottle would be outside the shop since they are a bit more difficult to move around. The same would be true by a manifold system of two 20lb bottles since floor space is also an issue as well as the difficulty to move two bottles connected together.

[Noitoen]

Should check this table

https://flameengineering.com/pages/propane-information

[mikey553]

I don't have a propane heater, but can offer you some theoretical explanation. Propane is kept in the bottles in the liquid form under pressure. There is pressurized propane gas above the liquid level. This is known as a saturated condition. The pressure in the bottle depends on its temperature. At 70 F it is 110 psig, at 40 F - 64 psig, at 20 F - 41 psig, at 0 F - 24 psig. I gave you just a few points, but any temperature has its corresponding pressure.

When the heater sucks propane gas from the bottle, the liquid propane boils trying to maintain pressure-temperature relationship. Boiling requires energy, so the bottle temperature drops and so does the pressure. At some point the pressure drops so much that the heater goes out. The only way for it to operate in winter temperatures is to get more heat energy to the liquid propane. This tlcan be accomplished by heating the bottle or by using a bigger bottle. Bigger bottle can get more heat from the surrounding air and will not freeze as quickly as a smaller bottle.

So this is the theory behind your problem. I have not done this personally, but I have worked with pressurized gases for many years and learned a few things along the way.

[deltap]

A propane dealer can tell you what size tank you need for that input. Depending on lowest temp I will guess 200-500 gal tank. Large installations require a vaporizer to maintain pressure on a heavy draw.

[Willy]

Here's link to a vaporization rate table for various size tanks at various temps and the amount in BTU that can be drawn at that temp.

https://flameengineering.com/pages/propane-information

I'm reminded of two incidents, one was when using two 100 lb tanks in 100° weather on an asphalt heater, even at that outside air temp both tanks would get about a half inch of frost at the liquid propane level in the tanks, felt good to rub up against them.
The other extreme was driving into a truck stop way up north at -40 and saw that they had a pile of burning tires around one of their 1000 lb. propane tanks in order to draw enough vapor from them to keep the place warm. Look kind of sketchy but it worked.

[eKretz]

Parallel the smaller tanks and you should be fine. That will reduce the flow from each and thus also the temperature drop. A dual manifold will probably do the trick depending on initial temperature.

I have in the past (on work sites with no heat in winter) also occasionally placed a single tank in the peripheral output from the heater so it's warmed a little by the output, that does the trick in a pinch, just be careful not to get it too hot.

[Dan Dubeau]

A 20lb bottle is too small for such a big heater IMO. I used to use 20lb cylinders for my turkey fryers to boil sap, but would run into the same issues of bottles freezing, and having to stick them in a barrel of water. I switched to 30lb bottles and the freezing problem is almost gone (will still freeze up when nearing empty). The fryers are only about 45000 btus. For your heater at around double the btu I would expect freezing problems no question. A 100lb cyl should be fine, but someone could do the math to be more accurate.

[darryl]

What is the temperature where the tank would be? A 100lb tank outside might be no better than a 20 lb tank inside- except for volume. Perhaps the best answer is to dedicate a hand cart to the larger tank so it's easy enough to move around. I wonder if there are any legal issues with having the larger tank inside- they don't even like you having a 20 lb tank inside.

When it comes to heating the tank to ensure that gas will keep flowing, there's a parasitic drain right there. A tank that's cooling as it's being used is going to suck some of the heat that you're producing. I wonder what the numbers show- if you maintain the tank (and it's contents) at say room temperature, what percentage of the heat being produced by burning has to go into maintaining the tank temperature? Would it be 5%, less, or perhaps more?

At any rate, 85000 btu seems like a lot for a 20 lb tank to handle. Assuming the tank didn't freeze, how much time would you get out of one fill?

[mikey553]

What is the temperature where the tank would be? A 100lb tank outside might be no better than a 20 lb tank inside- except for volume. Perhaps the best answer is to dedicate a hand cart to the larger tank so it's easy enough to move around. I wonder if there are any legal issues with having the larger tank inside- they don't even like you having a 20 lb tank inside.

When it comes to heating the tank to ensure that gas will keep flowing, there's a parasitic drain right there. A tank that's cooling as it's being used is going to suck some of the heat that you're producing. I wonder what the numbers show- if you maintain the tank (and it's contents) at say room temperature, what percentage of the heat being produced by burning has to go into maintaining the tank temperature? Would it be 5%, less, or perhaps more?

At any rate, 85000 btu seems like a lot for a 20 lb tank to handle. Assuming the tank didn't freeze, how much time would you get out of one fill?

100 lb tank is much bigger than 20 lb tank and its surface area is bigger as well. When tank cools down during heater operation the surrounding air supplies the heat energy to the tank trying to equalize the air and tank temperatures. So the bigger the tank and the bigger the temperature differential, the faster would be a heat transfer. You may be surprised, but the cold air at -40F contains a fair amount of heat energy. If tank surface is colder than the ambient air, the heat transfer would take place. This is my explanation as to why bigger tank can produce more gas than a smaller one at equal conditions.

As far as any legal issues with having the tank inside there may be some restrictions for that. I remember that many years ago in a city I used to live propane tanks were not allowed in the residential buildings. Separate machine shops may be another matter. You have to consult you local authorities if you want to be legal. Your insurance company may not like propane tanks inside the building either.

[Bob Engelhardt]

It's an estate sale heater, maybe a $180 100lb tank (Lowes) is too much. Do they do home delivery for something as small as 100lb? Otherwise a full 100lb-er is 170lb and would be kinda awkward transporting.

I would heat the 20lb-er with the heater. Find a sweet spot off to the side where the heating matches the cooling.

[Ohio Mike]

You need bigger bottles. But 100# cylinders are wicked heavy to move. I'd sell it and buy a kerosene heater, but that's me. I've used propane heaters indoors but I always feel sick later. Even for short runs. I don't have that issue with kerosene and its easier to get.

[eKretz]

You need bigger bottles. But 100# cylinders are wicked heavy to move. I'd sell it and buy a kerosene heater, but that's me. I've used propane heaters indoors but I always feel sick later. Even for short runs. I don't have that issue with kerosene and its easier to get.

Unless you're using a propane heater that is not running correctly that should not happen. Byproducts of propane combustion are water vapor and CO2. CO can be produced if air/fuel ratio is off.

Kerosene on the other hand produces a handful of other nasties in addition to those that are the same as propane.

Personally, I'll take the propane heater. Cheaper to run for the same BTU and no odor like the kero heaters.

[Gazz]

Thanks for all the comments. As I stated in my original post, a two bottle manifold is not desirable. A 30 or 40 lb bottle might work but I would have to buy one and since I have three 100 pounders which are certainly past their certification, I think I will go with those after recertification. They could also be connected by a manifold and plumbed to run the forge as well and located outside the shop. I'm not to concerned with the weight as I have equipment to aid me in moving them into location. And yes, propane is more desirable for me since the kero heaters do stink.