# Dual fuel freestanding stove with natural gas and 20 lb propane bottle (for emergencies)?



## dualfuel (Mar 21, 2021)

I would like to install a small (20Kish BTU) freestanding dual fuel gas stove.  I have read that most dual fuel stoves have separate ports for natural gas and propane. My plan would be to have natural gas as it's primary source, but  I would like the option to shutoff the natural gas line and connect a 20 lb propane tank in an emergency. I would plan to have the line to the propane tank go outside. It look's like there are products (e.g. Pleasant Hearth 23.5 in 20K BTU Dual Fuel Gas Stove) that could do this with a 100 lb propane tank, but I was curious if there are any that could use a 20 lb propane bottle. I realize a 20 lb propane bottle would only last about a day. I do not the option to store a 100 lb propane tank.  The home is a 6K feet. Thanks!


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## DAKSY (Mar 21, 2021)

ALL of them can use a propane bottle. I convert 3-4 units a week from NG to LP & fire them up on a 20lb tank to check for gas leaks.


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## dualfuel (Mar 21, 2021)

I guess my question is why then do they state "Propane use requires 100-lb tank or larger with two-stage adjustable regulator available from local gas company" I'm guessing there's some difference in release from a 20 lb tank that creates a risk.


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## DAKSY (Mar 21, 2021)

My guess would be that it has to be inspected by the local authorities & 
that a 100 lb tank is mandatory for an approved installation if you are burning
primarily LP.


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## dualfuel (Mar 21, 2021)

I think the regulations are motivated by a 20-lb tank not being able to vaporize enough, especially when the tank is near empty or cold or at high altitude or the stove is at high setting. So I think the concern is the stove not working. I found the propane vaporization charts on the internet

20 lb



			https://www.dvorsons.com/Magikitchen/pdf/LP_gas_guidelines.pdf
		


100 lb








						Propane Information
					

Propane Vaporization Chart, Properties and Combustion Data VAPORIZATION RATE - 100 lb. Propane Cylinder (Approx) Pounds of propane in cylinderMaximum continuous draw in BTU/hr at various temperatures in degrees F. 0° 20° 40° 60° 70° 100 113,000 167,000 214,000 277,000 300,000 90 104,000 152,000...




					flameengineering.com


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## DAKSY (Mar 21, 2021)

dualfuel said:


> I think the regulations are motivated by a 20-lb tank not being able to vaporize enough, especially when the tank is near empty or cold or at high altitude or the stove is at high setting. So I think the concern is the stove not working. I found the propane vaporization charts on the internet
> 
> 20 lb
> 
> ...




Ok. Good info to have, but I'm telling you that I can burn a stove FOR HOURS on an 20 lb LP tank,
without any issues.


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## clancey (Mar 21, 2021)

Do you think the altitude might make a difference?   6000 feet is over a mile high... clancey


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## DAKSY (Mar 21, 2021)

Ya got me there. We're at about 600 feet around these parts.
I know there are considerations when gas units are installed
"Mile High," but I believe the adjustments are made in the 
size orifices & ATF mixtures to perform correctly...


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## Lennox65 (Mar 21, 2021)

dualfuel said:


> I guess my question is why then do they state "Propane use requires 100-lb tank or larger with two-stage adjustable regulator available from local gas company" I'm guessing there's some difference in release from a 20 lb tank that creates a risk.


The important part of this instruction is that you NEED a regulator between the LP tank and the gas valve. You would probably have other problems with vaporization and adequate fuel delivery as these small tanks are not designed for this use, but the regulator is the most critical part.


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## DAKSY (Mar 21, 2021)

I use a simple gas grill connection to the tank at
the regulator end.. In-line shut off. Quick release at the 
other end to whatever connection I need..
You can run it like that for hours on end. 
You said yourself that you only needed it SOMETIMES.
So it doesn't have to be a permanent set-up. 
Run 1/2" Corrugated Stainless Steel (CSS) from the unit 
to the outside wall where you plan you tank connection.
Disconnect the tank when you're done &
shut down & seal the LP side.
If you decide to put in one or more LARGE LP tanks,
the connection can be used for that job


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## Highbeam (Mar 21, 2021)

I expect that high elevations would actually help the situation. It’s easier to boil water at elevation. Means more gas production. 

Then, the 20 lb tank has almost the same diameter as the 100lb cylinder. This means the liquid surface area is the same which means equal steady state gas production. Good way to think about this is that a 100# cylinder with just 20# of liquid in it, same liquid surface area, same production. 

I would have no problem using a 20# cylinder with the understanding that it has a small capacity of actual fuel.


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## ABMax24 (Mar 21, 2021)

Highbeam said:


> I expect that high elevations would actually help the situation. It’s easier to boil water at elevation. Means more gas production.
> 
> Then, the 20 lb tank has almost the same diameter as the 100lb cylinder. This means the liquid surface area is the same which means equal steady state gas production. Good way to think about this is that a 100# cylinder with just 20# of liquid in it, same liquid surface area, same production.
> 
> I would have no problem using a 20# cylinder with the understanding that it has a small capacity of actual fuel.



It has nothing to do with surface area of the liquid propane in the cylinder, but instead relates to the surface area of the outside of the tank and its ability to absorb enough heat from the surroundings to keep the tank pressure up. Having a higher mass of propane in the 100lb cylinder also helps, it takes longer for the tank temperature to drop, and therefore longer for the tank pressure to drop when supplying gas.

We have this problem at work, we use 500,000btu propane torches to heat steel prior to welding in the winter. Due to the evaporation of that large volume of gas the 20lb bottles get cold very quickly, and eventually pressure drops and the torches become nearly useless. Of course the colder it is the worse it gets, at -42c (-44f) you can hold propane in a bucket, and the tank requires heating to operate the torches. We have since switched to liquid propane torches, where a special bottle sends liquid propane to a coil placed around the flame, this boils the propane prior to being sent to the flame head for combustion.

Gas codes base minimum tanks sizes on this concept, they really don't care about fuel storage capacity, they just want to ensure the tank is capable of supplying the minimum pressure to safely operate the appliance.


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