Ok, they don't show 100# tank, but extrapolating from 200# looks like it might be a stretch for cooktop that might be pulling 50Kbtu/hr or so with all burners in use.
propane conundrum
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100lb tanks have a really small surface area. The tank is tall and thin so there isn’t much surface to evaporate from. A fatter tank will be able to evaporate more.
I'm not sure; a fatter (more resembling a sphere) tank will have less surface area relative to its volume.
The same volume in a cylinder has more surface area.
It’s not the sides that matter. It’s the circle where the liquid propane can evaporate. The top of the liquid. A wider tank has a circle with a larger area. I’m probably not saying this right.
No, it's the heat input that creates evaporation. The boiling does not happen at the surface of the liquid, it happens at the interface between liquid and metal tanks - that's where the heat comes in.
Like water boiling in a kettle or pot: the bubbles get formed at the bottom where the heat input is.
The surface area of the tank determines the heat input from the ambient environment. Bubbles will form at that interface (walls and bottom), and will rise to whatever small "top of the liquid surface" there is.
Same as having a beer bottle on a stove; the boiling will happen regardless of how narrow the neck is where the (small) surface of the liquid is.
It's based on the surface area of the propane tank exposed to the outdoor temperature that allows the liquid propane to absorb heat from the surroundings.
A couple square inches of surface area is all that is needed if the temperature is sufficient to boil the propane.
Keep in mind that chart is for steady state operation. A propane tank that is only used occasionally, say for half an hour a day to run a couple stove burners, can supply the required gas solely by its own internally stored heat.
We use 500k btu propane torches on 20lb bottles all the time, the torch works great for the first 5 or 10 minutes until the entire bottle cools off, then the rate of gas boil off is proportional to the amount of heat the bottle can absorb from its surroundings.
A couple square inches of surface area is all that is needed if the temperature is sufficient to boil the propane.
Keep in mind that chart is for steady state operation. A propane tank that is only used occasionally, say for half an hour a day to run a couple stove burners, can supply the required gas solely by its own internally stored heat.
We use 500k btu propane torches on 20lb bottles all the time, the torch works great for the first 5 or 10 minutes until the entire bottle cools off, then the rate of gas boil off is proportional to the amount of heat the bottle can absorb from its surroundings.
Interesting thoughts about phase change. I hadn't thought too hard about it and believed all the folks talking about "wetted" surface area. As though somehow the interface area between liquid and gas governed the rate of boil.
So really, a spherical tank would be the least ideal. You actually want an inefficient shape like tall and skinny.
I'm sure you noticed that you could turn that torch onto the propane tank to warm things up!
Wetted surface area to me means the area of the metal that is wetted by the liquid.
Only if you need a high BTU gas flow for the volume of tank that you have
Correct, only the surface area that contacts liquid inside transmits heat to the liquid. That’s why you can see the condensation line or frost area on the outside of a cylinder under load where the liquid is in contact with pressure vessel.
Horizontal tanks have more surface area across the bottom touching liquid as it gets low, which raises the pressure like a large pan with a little water across the bottom of a large surface area. The tank can still supply a 100,000 BTU furnace at 1 or 2 % where an upright cylinder may need 5 or 10% to maintain pressure at or below freezing temperatures. At -45*f propane ceases to boil, pressure drops, and you only have liquid in the tank with no vapor pressure, just like water below its boiling point in a bucket.
Corn dryers with very high BTU requirements use a supply tank heater to induce heat into the fuel to vaporize it. Literally heating the tank with a burner to boil the liquid faster than heat from the atmosphere can.
Liquid in the tank or cylinder cannot ignite since it is 100% fuel with no oxygen. A tank rupture that expels expanding ignited liquid into the atmosphere is called a bleve. An expanding fireball.
It is easy to experience pressure drop when changing valves and appurtenances on cylinders and ASME tanks. You open the outlet to expel vapor as fast as possible. (In a remote location) A few minutes roaring out, the wetted surface area frosts up. Tank wall is so cold the heat from atmosphere no longer boils liquid inside. Pressure drops and vapor slows. You remove the valve (above liquid level) and replace it in the tank or cylinder. Tank warms up coming back up to pressure. With smaller cylinders you can pour the liquid propane out and instantly freeze things, such as weeds or leaves, and shatter them with a gloved hand. It is clear liquid that bubbles and dances on the ground like pouring water on a hot stove boiling rapidly.
Fun stuff us propane guys do.
So back to this topic ... recall I've eliminated all gas appliances from my house, except the cooktop on our kitchen range. I'd like to get rid of the big 100 gallon tank and associated rental fees. Unfortunately they won't bring a truck to fill a 100lb tank and it's too big to cart into town every so often.
Turns out there's such a thing as a 40lb tank ...
... which would be small enough to be manageable for taking in to get re-filled, but large enough I doubt I'd have to fill it more than once or twice a year. (The last time my current 100 gallon tank was refilled was May 2023 (21 months ago) and it's currently at 48% (and I even used a little in my dual-fuel heat pump in winter of 2023-24 before I installed the new HVAC system). But I'll monitor how quickly that 48% falls now that the cooktop is the only consumer.
My question: what do I need to attach this 40lb tank to my house ? Right now there's one regulator inside the lid of the 100-gallon tank, which feeds copper tubing to a regulator on the side of the house (which feeds 10" WC to the black pipe in the crawlspace). It looks like the 40lb tank has the same kind of connection as the little 20lb under-the-grill type tank. And they sell hoses with one-stage regulators built-in for those. So maybe I can remove the one on the side of the house and feed the black pipe directly ?
Turns out there's such a thing as a 40lb tank ...
... which would be small enough to be manageable for taking in to get re-filled, but large enough I doubt I'd have to fill it more than once or twice a year. (The last time my current 100 gallon tank was refilled was May 2023 (21 months ago) and it's currently at 48% (and I even used a little in my dual-fuel heat pump in winter of 2023-24 before I installed the new HVAC system). But I'll monitor how quickly that 48% falls now that the cooktop is the only consumer.
My question: what do I need to attach this 40lb tank to my house ? Right now there's one regulator inside the lid of the 100-gallon tank, which feeds copper tubing to a regulator on the side of the house (which feeds 10" WC to the black pipe in the crawlspace). It looks like the 40lb tank has the same kind of connection as the little 20lb under-the-grill type tank. And they sell hoses with one-stage regulators built-in for those. So maybe I can remove the one on the side of the house and feed the black pipe directly ?
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I know a lot of people who have switched from 100lbs to 20lb tanks. I think all the “portable tanks share the same valve styles. The 100 and 20lb tanks do. A grill screws onto the outside of the valve whereas the stove will screw into the inside.
If you change your regulator, not a bad idea if it’s old, you can run 2 40lb or 2 20lb tanks and have a spare when they go empty.
When the guy at the propane shop mentioned swapping out the regulator I was like the old one works. He asked the age of it. I started thinking… Grandpa probably bought it used in 1952… How much are they? I can’t remember the price, but it was cheap.
If you change your regulator, not a bad idea if it’s old, you can run 2 40lb or 2 20lb tanks and have a spare when they go empty.
When the guy at the propane shop mentioned swapping out the regulator I was like the old one works. He asked the age of it. I started thinking… Grandpa probably bought it used in 1952… How much are they? I can’t remember the price, but it was cheap.
I’ll take a pic later of my setup. It’s -16 out now, and it’s warmer inside. I’m burning down coals, so it’s not as warm as I’d like it, but comparatively speaking, it’s pleasant, lol.
The smaller tanks still have the older inner threads. My 40lb and 20lb tanks all do.
My 100lb and 420lb/120gal tanks have inner only. They are not meant for BQ use.
Just switch your regulator over.
BTW, inner threads have reversed threads.
My 100lb and 420lb/120gal tanks have inner only. They are not meant for BQ use.
Just switch your regulator over.
BTW, inner threads have reversed threads.
I'm in the hills, west of you. About 1400-1500 of elevation. -1* with a real feel of -7.
What a difference here with no winds. The cold must have settled in your valley. LOL
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Damn guys, you're making me cold. It's 50 and sunny this morning here.
Stay warm.
Stay warm.
You could look at forklift tanks. 33.5lb and 43.5lb. You'll need adaptors for the connection. My boss has a 100lb tank for his genny and I got him an adaptor to the DOT tanks for if he gets caught in a pinch.
Where can I find those? I have one about a 3rd full. Been hanging around in my stuff for 15yrs. It's always outa sight...outa mind,
Till you dug it out into memory....LOL
The pic missing the cylinder is a bbq regulator. Not for use with automatic burner regulation such as a thermostat, or indoor use. Two stage is required. The change-over in first pic is a two stage regulator.
The single stage is more susceptible to freezing at the orifice. It gets cylinder pressure and drops to about 1/2 psi (11 inches WC) in a single drop.
The first stage reduces cylinder pressure down to 10 psi, so the second stage only regulates from 10 psi or lower, having no problem maintaining 1/2 psi coming out, all the way down to 1/2 psi coming into the second stage. The more stages, the more accurate and more capable the regulation.
Think of a single stage having 200 psi supply set to 1/2 psi out. What do you have at 50 psi coming in? Maybe half of what it should be.
Now set a first stage regulator with 200 coming in, set at 10 psi out. The second stage can be accurate with 10 coming in. Drop first stage supply to 50. It may put out 5 psi. The second stage is still accurate with 5 coming in down to 1/2 out.
They only have an apartment sized stove in there. I guess they have a thermostat on it if they use an oven. Something like this one from my cabin.
The cabins aren’t set up for year round use. Mine is more like really nice winter tent camping. I drill a hole through the ice for water. It suits me though. I could easily live up here all year. My wife and kid, not so much. The kid would be better at it than the wife.
The cabins aren’t set up for year round use. Mine is more like really nice winter tent camping. I drill a hole through the ice for water. It suits me though. I could easily live up here all year. My wife and kid, not so much. The kid would be better at it than the wife.
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So, anyways, I figure I can just get a QCC1 to NPT hose and plug my 40lb tank into the first-stage reguator that was attached to the 100gal tank, so then I'll have two-stage regulation; I gather it's considered un-cool to use a single-stage regulator in a house (as opposed to a barbeque grill or RV).
But I also like the idea of twin tanks. I just need to find a changeover valve that either has just a first-stage regulator (instead of a single-stage one) or no regulator at all. So far all the ones I can find have a single-stage regulator. Can I feed that into the second-stage regulator on the house ? IOW, does the second-stage regulator have a minimum input pressure that's higher than its 11" WC output ?
Or is something like this considered acceptable for under-the-house use ?
But I also like the idea of twin tanks. I just need to find a changeover valve that either has just a first-stage regulator (instead of a single-stage one) or no regulator at all. So far all the ones I can find have a single-stage regulator. Can I feed that into the second-stage regulator on the house ? IOW, does the second-stage regulator have a minimum input pressure that's higher than its 11" WC output ?
Or is something like this considered acceptable for under-the-house use ?
RV’s require two stage.
There is a simple Tee that has a rubber disc that goes back and forth between the two sides. Male pipe thread that goes into regulator, and inverted flare for pig tails with POL ends for cylinders.
“Dual tank manifold tee”
This; https://www.etrailer.com/Propane-Fi...BIEeCzGUJySDD5XkX8wudk29md4KIF8RoCx6gQAvD_BwE
Doesn't really look like a tee, but I guess it is. What controls the rubber disc that switches between the two sides ? Does it allow refilling one tank without turning eveything off ?
So I'd either snatch the first-state regulator from the propane company's tank when they remove it (but it's really old), or buy a new one, and plug this into it. Then connect my two 40lb tanks to it.
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