I need help from a plumbing savvier for connecting propane gas to the new tankless water heater.

[jkk]

I just purchased a propane tankless water heater that would replace the existing 40 gallon water heater.
The New one has a vent fan which is called a power vent system.
So, I am going to use the existing 4" vent pipe with a 3" adapter. because the power venting system does not require direct venting like 3" x 5" venting.

My question is how to connect propane gas connections.

The new heater requires the Min 8.0"WC(1.99kPa)- Max 13.0" WC(3.23kPa=1/2 PSI).
" If the heater's supply pressure is greater than the specified maximum, a pressure regulator is required. The regulator must reduce the gas pressure to within acceptable limits"

My house propane tank has a first stage regulator as seen in the picture that would be 7-8 PSI or something like that.
That is the reason the existing heater has a regulator as seen in the picture below.
Should I use that old regulator for the new heater or have to replace it?
The new heater required 100,000 BTU and the old one is 75,000 BTU
Thanks in advance.
John

 

[havasu]

I may be wrong, but many experts here will recommend that you contact the tankless water heater company for specific pressures, and verify it is within the standards of your propane company. As we all know, gas can be dangerous, and the experts that spend countless hours trying to help others in here would be skeptical offering advice which could be incorrect, causing injury and/or death.

 

[jkk]

I found very helpful answer for my question as following.

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 0.5 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.

 

[FGMNTech]

I found very helpful answer for my question as following.

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 0.5 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.

1st stage at @10psi, and 2nd stage @11"WC (outside building) on a low pressure system or 1st @10psi and 2nd @2psi(outside building), and (inside building) Maxitrol @11"WC on a 2psi system. California max pressure going into a building is 5psi, but that might only apply to commercial applications, residentials likely limited to 2psi. The tan regulator in between the tanks in the OP picture looks like an old single stage reg that brings tank pressure down to low pressure (11"WC) right away. That likely wont be adequate for the new water heater depending on line type and sizing, but the OP should contact their current propane supplier about having the the tank regulator replaced anyway. Pushing almost 50 years old.