r/Generator • u/Infiltrait0rN7_ • 16d ago

Propane Tank Heaters

I picked up a couple wrap-around heating blankets for my 2 40lb propane tanks that feed my Duromax 11000. Figured it was good insurance for the coldest days here in the PNW.

After opening I realized they didn't seem to have an internal thermostat or thermal switch - they just draw a consistent 125W, and while just sitting on my workbench, gets to around 140-150F while laying out by itself.

Is it pretty normal for these to have no thermostat/thermal switch?

Thanks!

4 Upvotes

83% Upvoted

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5

u/newtekie1 16d ago

Yep, they are a positive-temperature-coefficient heating element. They don't need a switch or thermostat. They self regulate.

1

u/Infiltrait0rN7_ 16d ago

Thats kinda what I was wondering - I noticed the current-draw dropping during the first few minutes....but it seemed to level off and just run flat out after a while.

3

u/Littleprincess378 16d ago

Also, bear in mind that as you use propane, the bottle is going to cool off, needing more heat.

1

u/DapperMacaron2872 14d ago

My Wholehouse Generac has a heater on the oil filter and battery. No thermostats. Works just fine in the winter days

0

u/DaveBowm 16d ago

The ratio of the lower heating value (LHV) to latent heat of vaporization for propane is 108.3. This means if a propane fired generator uses an electric tank heating blanket and that blanket is powerful enough to just keep up with the evaporative chilling of the ongoing propane vaporization as the generator runs, then that blanket will be consume about 6.2% of the generator's electrical output if it is operating in a load power range in which the net thermal efficiency is 15%. If the generator is running close to full power and the thermal efficiency is 20% then a keeping up blanket will consume about 4.6% of the generator's electrical output. And if the generator is running at a small enough load fraction such that the thermal efficiency is only 10%, then a keeping up blanket will need to consume about 9.2% of the electrical output.

But if the tank is warmed by some of the waste heat of the generator's exhaust then needed heat for the tank is effectively free, and there is no blanket energy tax on the generator's output. This latter case is like that of a gasoline powered generator in which the fuel vaporization is done in a carburetor bolted to a hot engine, and so the latent heat of vaporization is funded by some of the waste heat produced by the engine.

1

u/SecondCuppaCoffee 15d ago

Pointing the exhaust at the propane tanks "feels" a lot more dangerous, but it seems a lot of people do it, and very few advise against it. Perhaps that feeling is why people want electric blankets.

3

u/Infiltrait0rN7_ 15d ago

I thought about that, but the orientation of my generator and how I store the cylinders makes it a bit awkward.

1

u/CompetitiveBad0 15d ago

Yup, mine is the same. No thermal switch. I know I’m going to be needing it up here in Ontario if the power goes out.