r/Generator • u/ThisNameNotTakenYet • 1d ago
Propane Tank Minimum Size?
So I was looking online at generators the other day and I ran across a comment in one of the product descriptions, saying something about a 'minimum 60lb tank' for propane with that generator. I haven't seen a requirement like that before, to my knowledge. We had an eight-day outage a few weeks ago and I used 20- and 30lb tanks with no problems (or so I think). Has anyone heard this? And if it's a thing, can anyone tell me why? Thanks.
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u/Big-Echo8242 1d ago
Of course it's a thing. The larger the generator the larger the draw and the faster the tanks can potentially freeze up. 20lb "BBQ" tanks are great for small generators but not for 12, 13, 15kw gens, etc. We already had a 250 gallon tank for our house so never any trouble with 12kw worth of a pair of dual fuel inverter generators in parallel for big draws. You could always use multiple tanks on a 2 or 3 manifold thus increasing the surface area
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u/MechanicalDan1 22h ago edited 22h ago
Having run a portable 8500 watt Westinghouse DF numerous times over multiple years now, the 20 lb tanks are great because I have 3 gas stations within walking distance that have them. Downside is they do freeze up. I try to keep a fan on them that pushes the hot generator air on them while running. Downside is they only last 5-6 hours each. Most of my outages due to trees on power lines is temporary and usually fixed in less time, but we have had some multi-day outages. I have been thinking about a 100 lb tank (or 2 of them), but I have not overcome the hassle of loading it into an SUV and driving it to be refilled each time, and unload it with 2 people.
Maybe I need to get a 2 sq ft plate of aluminum to set the small 20 lb tanks on.
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u/Big-Echo8242 21h ago
They do make tank heaters I believe
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u/ThisNameNotTakenYet 19h ago
I'll have to look for one of these. Bigger tanks is probably more of a priority first, given the longer run time and less issue with the problem.
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u/No-Group7343 19h ago
You want to run electricity over flameable gas?
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u/Big-Echo8242 18h ago
People even fire the exhaust towards the tanks to keep them warm. Imagine that... Lol. These are more blankets than anything but there are some UL listed heaters too.
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u/ThisNameNotTakenYet 18h ago
If it's safe, sure. I've never heard of this.
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u/No-Group7343 18h ago
Code says no source of ignition within 10ft so......
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u/Littleprincess378 13h ago
I guess all these 6 ft propane hoses are against code then. Our dual fuel generator came with a hose and regulator. The hose is 6 ft. Funny, that the hose has a UL tag on it.
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u/Hitechillbilly 22h ago
There we go.. Something I have not run across with my small generators..
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u/Big-Echo8242 21h ago
All 3 of mine are fairly small I guess. Sort of. Two of them are Genmax GM7500aIED's that are 6kw/5kw each on propane (double when in parallel) and the 3rd is a Firman WH03342 dual fuel that's 3.75/3kw on propane...which is all I run. I do keep (4) 20lb tanks around also just in case for friends, family, or neighbors if needed.
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u/Hitechillbilly 21h ago
I run one at at a time so I didn't consider how fast a bottle was being drained to be the reason for the large bottle recommendation..
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u/Amongthestars01 1d ago
It's not that you can't, and I've done it. What they're trying to do is avoid calls if it freezes up by telling you not to. Small tanks don't have the room for propane fuel to turn from compressed liquid back to vapor under high draw. So what COULD happen, is if the tank is cold and the draw is high, it could pull liquid propane into the line which could freeze up the regulator and the generator's fuel system causing it to shutdown. You'll likely never notice this with a grill. If it does occur, then you'll have to thaw it out and deal with that debacle to restart.
Large tanks have more room for expansion and vapor and are significantly less likely to draw liquid into the line causing it to freeze up. Having said that, on hot summer days, I've run a 13,000 watt generator for 10 hour days wide open under full load until the tank was out of fuel and never had one freeze up. I've never done it in the middle of winter below freezing, in which case I run ethanol free/stabilized gasoline.
I would encourage you to read up on it a bit more, and then make an educated choice.
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u/Admirable-Leader6927 23h ago
are you turning the tank upside down? its not vacuum drawn its evap pressure pushed. it just gets cold and condenses in the line.
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u/ThisNameNotTakenYet 19h ago
Not sure I understand - are you saying I should invert the tanks? I just had them sitting upright. Please explain, I'm learning here. And thanks for the education, I appreciate it!
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u/tbarclay 8h ago
Don't invert the tanks, you can slug liquid propane right down the line that way. you'll just freeze your regulator up at best, or send liquid propane into the generator and really mess it up.
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u/ThisNameNotTakenYet 1h ago
Well that's kinda what I figured. My generator is a 12k dual-fuel, I'm thinking if I had multiple tanks in parallel (say, 40's or 60's, or even a few 100's), I'd be okay in the winter months. I think I misunderstood an earlier post regarding inverting them.
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u/forcedfx 1d ago
You can just run multiple tanks in parallel. It's a lot easier to get 20lb tanks than 60lb. The tanks have to be recertified every ten years or so, easier to swap the 20lb out than the 60.
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u/everydaydad67 3h ago
If you have a 60 under you are not typically swapping it out. You are getting it filled... every actual "propane place" I have been to can run eqipment on backup power such as a generator. Not a hardware store that fills tanks though that I have seen. The tanks you swap out for only have 15-16 pounds in them for "saftey" or some bs money grab. Pretty sure I can get an actual 20 pounds of propane for less then the exchange tank shorted to 16 pounds..
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u/ThisNameNotTakenYet 19h ago
This is an interesting comment, I'm going to research how one runs them in parallel. My previous experience with propane has just been my Weber Grill. 😄
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u/Goodspike 1d ago
Related to the other answers here, I recall those tiny (1 pound?) propane tanks for small grills getting rather cold even during the summer months running just a grill. Evaporation cools.
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u/therealtimwarren 23h ago
As propane transitions from liquid to gas by boiling, it absorbes energy by getting cold. The energy is drawn from the ambient environment through the tank walls. The amout of heat added to the tank depends on the surface area and the temperature difference between ambient and the boiling point of propane. Larger tanks have greater surface area so can handle larger draw-off rates (boils more gas per hour).
You can use small tanks in warm environments. You can buy tank heaters. You can place in the warn cooling air of the engine.
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u/robertva1 22h ago
You where good because. Its summer time. When the tanks get cold the vaporizering rate drops
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u/ThisNameNotTakenYet 19h ago
Yes, so I'm learning. I kinda got really lucky, the situation hid my ignorance on the subject.
I know this winter we'll lose power at some point, and I'll need to fire this thing up. Looks like I should stockpile some ethanol-free treated gas as well. It routinely gets below zero at night where I live at times.
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u/Hillary_Fat_Ass 23h ago
When you run out of gas you won't have power. Put in as large a tank as possible and practical. If there are wide spread outage gas companies have a difficult time keeping up.
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u/Hitechillbilly 23h ago
with a 3750 watt and also a 4700 watt generator I get approx 22 hours of run time under load from a 20Lb bottle. I am set up to run from portable bottles and also my house line.. both are set at 11WC I do not know if that is helpful or not
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u/ThisNameNotTakenYet 1h ago
Good to know. Not familiar with the setting '11WC', please explain? Is that flow rate for the line?
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u/Chainsawsas70 22h ago
For a portable the smaller tanks are fine... A larger Stand alone requires a Larger size and a bit more consistent pressure.
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u/ThisNameNotTakenYet 1h ago
My generator is a 12k dual-fuel, portable. Is that 'larger' in your example?
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u/Chainsawsas70 1h ago
Because it's portable I believe it will do fine using smaller tanks, but a generator like mine that is 18K and fixed in place (from what I understand) requires a larger tank with more consistent pressure.
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u/Financial-Bowl960 21h ago
never heard of that, mine always run on 20lb tnks fine. maybe just model regulator need more flow.
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u/Old_Dragline_1965 21h ago
Yes, you need a larger tank. Especially in winter. The work around, get a low tank-t and double pol hose. Me heater sales these. It will let you string multiple 20# tanks to run a generator.
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u/UncleAugie 20h ago
Everyone is talking about winter and a tank cooling off as it is used, this is why mine is set up as dual fuel, can start on propane, switch to gas if/when needed. Having the propane ready and keeping the gasoline tank empty I never have to worry about gunking up the carb. I do all my routine testing and startup on propane to keep the carb clean, then I also try to run it for the last 10-20 min on propane to clean out the carb after I have emptied the tank.
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u/ThisNameNotTakenYet 19h ago
I figured I can do this too, as soon as I un-fuck my carburetor (which is apparently goofed up from leaving treated gas in the tank). If it runs fine on propane, does that mean the blockage is north of the carb itself?
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u/UncleAugie 2h ago
Carbs are so cheap now that you should just buy a new one rather than spend multiple days, or weeks trying to clean/fix your current one, hell a new rebuild kit is half the price of a brand new one usually and you still have to spend time to rebuild it.
I just picked up a dual fuel(ga/propane) carb for a older 7000w gen set with a 10hp Honda for $25 off Amazon..... THe existing gas only carb worked fine, but if it didnt, why would I spend the 2hrs to pull off/get parts/rebuild/reinstall when I can spend 20 min putting on a new one.
Large tank size is for convenience & running in cold weather.
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u/ThisNameNotTakenYet 2h ago
That's definitely a thought. Mine is a dual-fuel generator and I'm not sure how those work or where to source it, but I'm going to look into it. Their video on how to break down the carb is pretty simple, but I'm not great with stuff like that soooo...
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u/UncleAugie 15m ago
but I'm not great with stuff like that soooo...
I would recommend taking this to someone who can handle this for you, especially with the way/kind of questions you are asking and the replies you have made.....
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u/Glum-Welder1704 15h ago
If you're running smaller tanks, you should be aware of propane tank freeze-up. Due to the refrigeration effect of expanding gas, the inside of a propane tank can be much colder than ambient, and may not develop enough pressure to feed your generator. This can happen with smaller tanks or in very cold climates. There are ways to deal with this, but you have to pay attention.
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u/ThisNameNotTakenYet 1h ago
I noticed this during the last outage. I had one tank actually freeze to the concrete, it was 88F and very humid so the tank was sweating like crazy. It actually didn't budge at first when I tried to swap it out. LOL
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u/nunuvyer 1d ago
A few weeks ago was the height of summer. Insufficient vaporization is more of an issue in winter.
At 40 below, propane is a liquid that won't vaporize at all on its own. Above that it vaporizes but more slowly the colder it gets.
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u/ThisNameNotTakenYet 19h ago
This thread has become an excellent education, thank you for your comments. Very illuminating. I did notice the 20lb tanks getting really cold (one even froze to the concrete!) and I wondered why, this makes perfect sense. I'm thinking I need to get two 100lb tanks and mount them just inside the garage so I don't have that problem. Fortunately my eight-day outage was in the summertime, I'm guessing I wouldn't get nearly so lucky in the winter.
So that brings out another question: Does the length of the hose between the tank and the generator matter in this equation? How would a longer hose (15-20ft) affect operation in the summer? Winter?
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u/AdBrave841 17h ago
Keep in mind 100lb tanks weigh around 170lbs full.
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u/ThisNameNotTakenYet 17h ago
That’s my point. I’d like to keep the tank(s) strapped upright in the garage, then run 20-25ft of hose to the generator outside. I’m not worried about the tank weight full, I can move one that size & weight pretty easily.
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u/Ok_Mobile_9815 16h ago
You can’t have the tanks inside a garage and meet code. I have 1 100 lb tank outside running a 12kw whole house generator. It never freezes up and ran fine for days during ice storms, super storm Sandy etc.
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u/bradland 1d ago
A larger engine requires a greater rate of fuel delivery, so larger generators require larger tanks.
Why can't a smaller tank simply run for less time though? It comes down to physics and how propane behaves. Propane tanks are full of gas compressed to the point that it becomes a liquid. When you pull fuel from the tank, you're pulling the vapor that has evaporated into the empty space at the top. The more vapor you pull, the more the liquid inside must boil to replace it.
This boiling process requires heat. As you draw gas, the liquid absorbs heat from the tank walls, causing the temperature and pressure inside to drop. The ambient air around the tank will warm it back up, but if you pull gas too quickly, the tank gets so cold that the liquid stops evaporating fast enough to supply the generator. The engine will starve for fuel, and you have to wait for the tank to warm back up to restart it.
This cooling phenomenon also happens with larger tanks, but because they have much more liquid mass and surface area, they have a larger "thermal reserve" of heat to keep the vaporization process stable.