Two or three parallel 40's help.

Make the manifold from pipe and fittings and good pipe dope (not teflon tape)

I seem to also be in a borderline situation.  I have a 100 gal upright tank, and a 20 gal as a reserve.  The cabin has a 100K on demand water heater, a freestanding range, and an 18K furnace.  When the temps were high 30Fs to low 40Fs, and the 100 gal tank was "full" I had hot water in the shower, the washer, and the kitchen sink...the stove and furnace works just fine.  Then the tank gauge dropped below 70%.  Hot water for the washer, but tepid water in the shower and kitchen.  Bummer.  Now its 28F, I'm wondering if the washing machine will still get hot water.  On the full 20gal tank there is never more than tepid water at any faucet.

The furnace and the stove continue to work just fine, surely because their demand is much lower.  Maybe the answer is another 100 gal tank running in tandem w/the first.  But maybe that is only a "step up" and not a absolute solution that will work when the temps get down to 8F at night.  Certainly I use more propane in the winter, and a hot shower to warm up in the AM is a sweet proposition. 

This setup worked very well in the 5th wheel. Sigh

These two charts (also appears in the original post along with some others) explains what is happening when the tank level decreases and the temperature drops. The ability to supply propane in quantity diminishes. The RV water heater likely only drew 13 to 15 thousand BTU's. The on demand, demands many times more. You may be lucky that the burner works at all.

Thanks. I did read them at the beginning of this thread and they clearly show the imbalance between supply and demand.  I need to put my math head on and figure out the most cost effective way to augment the system so it will work under all likely circumstances here. 

Just to be clear, the tanks are 20 gal, which I think is 100# and 100 gal which I believe would be 400 or 500#.  Still, though, borderline and not functioning well at these lower temps.

FWIW, a horizontal tank will be capable of supplying a greater volume of gaseous propane than a vertical tank. This is because of the greater surface area of the liquid propane in the horizontal tank. The figures in the charts are for vertical tanks.

Note: it can be dangerous to place a vertical tank in the horizontal position for any reason as Okie Bob indicated, unless it is completely empty. The reason has been mentioned someplace here before, but bears repeating. The reason is the safety pressure release valve is located at the tank top. When laid on its side the relief valve may be in the liquid area. If the pressure rises and the valve releases pressure it would then release a stream of liquid propane. Liquid propane on the skin can freeze instantly as it evaporates. When liquid propane is released to the atmosphere it multiplies in volume and could cause a large fireball/explosion.

This is as good a place as any to add this tidbit of information.


How much water is produced when propane burns?

Calculating this from the chemical formula for propane it looks like for every gallon of propane burned, 1.64 pounds of water is produced.

In liquid form that is 25 ounces of water per gallon of propane used.


Another good reason to use vented propane heaters in a cabin/building.

"I have a 100 gal upright tank, and a 20 gal as a reserve.  The cabin has a 100K on demand water heater, a freestanding range, and an 18K furnace.  When the temps were high 30Fs to low 40Fs, and the 100 gal tank was "full" I had hot water in the shower, the washer, and the kitchen sink...the stove and furnace works just fine.  Then the tank gauge dropped below 70%.  Hot water for the washer, but tepid water in the shower and kitchen.  Bummer.  Now its 28F, I'm wondering if the washing machine will still get hot water.  On the full 20gal tank there is never more than tepid water at any faucet."


Ok, I'm not a plumber.  I figured out what the main problem is by accident.  My washing machine is a super compact and only has one inlet, so the hot and cold water hoses coming out of the wall are hooked to a "Y" which is subsequently attached to the washer inlet.  This is upstream from the shower and the sink.  If both of the washer faucets are open when I try to get hot water from the shower or sink, cold water gets through the Y joining up with the hot water, making the downstream hot water tepid. 

This does not solve the problem of a low tank combined with low temps, but gives me a little more time to invest in another 100gal tank. 

Good sleuthing!!   

A lot of useful information here I came across on a search on propane tanks. I recently installed a propane conversion kit on my backup power generator. It's working quite well so far. I've been looking at getting a 40# tank as soon as Costco gets them in again. On the other hand, it seems that having two 20# tanks might provide a couple of benefits: I can change a tank at a time when necessary without shutting down the generator, (if it's properly connected) and it seems it will provide that extra vapor that might be necessary at low ambient temps. I think there may be a connector that I could use from Mr Heater to attach two tanks to one appliance, but I need to verify that a single tank can be removed without leakage. A simple manifold would not work totally for this, but one with connections that will shut off might. The only regulator is a two stage on the generator, so I guess I could put a two outlet block on there and run two separate hoses, one from each tank. This would be full tank pressure, so anything I use needs to not leak during a tank switch.  Any suggestions would be appreciated. Thanks.

Can't you just put ball valves in line past each tank? 

Most RV supply stores have a selector valve that lets you chose which tank you want to run. You can disconnect the other side take it off the mount and take it down to refill.  When you run out in one tank it automatically switches to the other take and will display a red band and a green band in a sight glass.  Two red bands that is bad - no fuel available.         

Thanks MountainDon that would actually explain an issue I have been having with my camper heater.  It is also a good jumping off point for me to ask my propane dealer before I bring in my two 500 gallon tanks.

Thought I would post a recent cautionary experience. I have automatic changeover regulator similar to the one pictured above and recently experienced an unexpected leak in the rubber hose at the juncture of the metal fitting. Apparently this is not an uncommon failure point. As luck would have it the leak occurred on the side that I had the switch set to, it slowy emptied my 100lb tank and then switched to the other full tank and then also started to drain it. Apparently if the regulator is auto switched(not manually)  there seems to be a pressure connection between the two sides. Probably lost around 80lbs before I noticed. The hoses were no more than 3 years old. Lesson here is check/leak test you rubber lines frequently and be sensitive to low flow propane symptoms especially in context to having propane still in the tank. This low flow rate is a feature built into the regulator when they perceive a leak. I obviously ignored mine.

Hello all,

I've just found this site as I was looking for vaporization rates.  I know this is a few years later, but I imagine propane hasn't changed much.  I have a question about the tables shown earlier. They seem to be quite approximate since one shows BTUs of about 25000 and the other of about 40000 for 100 lb cylinders at 25% and 0 degrees.  That is a 60% difference.  Which might be more accurate?

Thanks

The rule of thumb used by Arrowhead suggests that for a 100 lb tank (47" x 14" or so) the 40,000 is closer.  Depending on your application, you might go by whichever is least advantageous.

http://www.arrowheadlpgas.com/documents/VaporizationChart.pdf

Question: I live in the city and my house is totally electric.  I am worried about having absolutely no source of backup heat.  I wanted to find a low-BTU freestanding ventless propane stove that I could run off of a portable propane tank (50 pounds or less).  It would be great if it could be visually appealing so that my better half would approve of the purchase    The Pleasant Hearth Vent-Free Dual Fuel Stove — 20,000 BTU, Model# VFS-PH20DT (you can find it at Northern Tool), seemed like a perfect fit.  However, they say that it will only run off of a 100 pound tank.  My initial reaction was one of disbelief, because most outdoor gas grills pull 30 to 40k BTUs and run off a standard 20 pound tank.  My conclusion, after some review, is that so long as the tank is kept indoors (I know that some of you all will freak out about this suggestion) at an ambient temperature of no less than 60F, I would be fine with a 30 or 40 pound tank, so long as I never let it drop below 30% full.  Any freeze-up concerns, were the tank to drop below this level for some reason, would be addressed by the standard safety valve.  Am I missing something here?

    Scary post!  If I were ever doing a primary search for victims during a house fire and encountered a 100# cylinder I'd immediately order all other firefighters to evacuate.  There are many, many cautionary tales of leaking cylinders.  The regulators bleed off fumes and are intended to be kept outside.   In fact, they must be 3' from any openings into the house.
    Please do not put a vent free heating unit in living quarters!  If your house is very, very drafty you might not get CO poisoning.  If it IS very, very drafty, spend your money on making it less so...
    I realize this isn't what you were asking.  However, there are some very attractive direct vent wall heaters and fireplaces that will keep you warm and safe.  Installation isn't difficult.  The vent system goes out the nearest wall and pulls combustion air in the same place. Options for your propane tank include burying, electric heat blankets, insulated storage, or multiple tank cascade systems (which increases your output when it gets cold)
    Another option---have you considered a backup generator?

Id really like to be able to hook my 40 lb propane tank up to my generator without using a cheapo 3/8 grill hose and lp regulator.  I'm not able to find the correct hardware to go from the larger threads on tank to a 1/2 ID pressure regulator.  Im wondering if I'm searching using the wrong terms or what, can anyone help me out?  My generator calls for a half inch supply.

I have found some hard to find fittings here and here.

Bingo, just what I needed thanks Mt Don

http://www.namic.org/learn/FILP_manual/Chapter_4/4_6.htm  There may be a way or provision to direct the regulator vent outside while keeping the tank inside.  It's done on boats pretty often.  Come to think of it, we respond to quite a few boat fires...

This thread sort of clicked a light bulb in my head. In colder climates, I am finding that instead of the 500lb above ground cylinders, many use in-ground 500lb or 1,000lb tanks. I thought this was purely for aesthetics. Is this for keeping the tanks at a much higher temperature in ground than above ground in the bitter sub zero cold?

That's exactly why.  The thermal mass below the frost line provides enough geothermal heat to make up for the heat lost in evaporation.  Metal tank exposed to subzero air, not so much

Sadly, that's not really an option up here.
Our area is built on solid granite.
My propane tank is located where the snow blows in and covers it up.
This helps to keep it from getting too cold.
Others use heated blankets that cover their tanks.