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I am going to hook a tankless water heater to a 20lb propane tank. Do I need a regulator coming off of the propane tank?

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@Pigrew is right in the comments. My previous answer was wrong and dangerous. Do not supply 30 psi of propane to a tankless water heater.


New Answer:

According to Rheem (a manufacturer of tankless gas water heaters) and The West Virginia Propane Gas Association, modern homes have a 2 psi supply line from the meter with regulators on each piece of equipment to lower the pressure more. Older homes could have a much lower pressure from the meter negating the need for regulators on each piece of equipment.

Pressure in a propane tank, large or small, can range between 100 and 200 psi.

An example tankless water heater specs list a maximum gas pressure of .5 psi.

Once we get into pressures this low, people start using the unit inches of WC (Water Column) instead of psi. The standard pressure that household appliances typically need is 11" WC.

You will need two regulators.

You will need one regulator to take the tank pressure (up to 200 psi) to down to a household line pressure (2psi). You will also need a regulator to take the household pressure down to the 11" WC needed by your hot water heater. The reason you need two is because that is a large pressure difference and there are limits to the abilities of regulators.

There is a bit of fudge factor though. You could get a regulator that outputs 10 psi fir the first one if you can get a regulator with an inlet pressure over 10 psi (and outlet pressure of 11" WC) for the second one.

There is another factor to consider when choosing a regulator: flow rate.

All of this adds up to the suggestion that you call a professional because explosive compressed gas in your home where your family sleeps isn't the best thing to be playing around with.

  • Is there a certain type of regulator I should use? – Steve Jun 18 '15 at 21:44
  • The required water pressure is 20PSI. The required fuel pressure is generally MUCH lower. Supplying 20 PSI to the appliance would be VERY dangerous. – Pigrew Aug 25 '15 at 4:19
  • @Pigrew Thank you very much for pointing that out. I deleted my dangerous answer and wrote a completely new one. I apologize to anyone who was misinformed by my naivete. – Zach Mierzejewski Aug 25 '15 at 15:27
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In order to use propane, the appliance needs to be converted, and you will need a regulator:

By default, most gas-fueled appliances are sold configured for natural gas (methane) and NOT propane. Because of the chemical differences, propane requires a different ratio of fuel to air in order to burn properly. This is accomplished by changing the fuel nozzle in the appliance. Most appliances will come with both styles, so often you will already have the parts that you need for this. If it is reconfigured, the flame temperature will be wrong and soot will be deposited.

The second thing to worry about is the pressure. Propane tanks provide 100-200 PSI. If hooked up directly to the appliance, it WILL damage the valve and regulator inside of the appliance. One water heater I just examined requires a pressure of between 8 and 13 inches of water for propane. Your water heater is likely similar, but do check its manual. This required pressure is approximately 0.4 psi (very low)!

The regulator will have to be sized properly based on the flow rate needed and the pipes used.

Also, be sure to store your propane tank outdoors. They are not designed to be stored indoors. You may want to buy an outdoor water heater. Because of safety issues, you may want a professional to do the plumbing.

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The regulator for a Camco Wave Heater is 0.4 pounds (11 in. wc) and commonly available. Also, is rated up to 70,000 btu/hr. Just purchased one with hose for around $30 and is connected directly to a 20 lb, propane tank.

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