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I'm looking at a tankless hot water heater (Rinnai V65EP) with a 3/4" NPT propane input. The manual says that a 1/2" propane feed is acceptable if it is relatively short. Required gas supply pressure is 8.0 ‐ 13.5 inch W.C.

I am planning on putting a dedicated 40lb (10gal) propane bottle right next to the water heater. The propane line will only be a few feet long, and the water heater will be the only appliance drawing from this tank.

Is this a workable plan?

What regulator and other equipment should I install between the tank and the heater?

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Is this for occasional, light duty use? I assume you have no teenagers.. ;-) – HerrBag Aug 20 '13 at 22:33
Why do you say that? – Jay Bazuzi Aug 21 '13 at 0:44
One estimate I saw claimed an 800K BTU capacity for a 40lb bottle.. It just seems small. How long do you estimate a bottle will last? – HerrBag Aug 21 '13 at 12:41
A BTU is used to raise 1 pound of water 1 degree F. 8.3 pounds in a gallon. Raising the temp 70 degrees (from 40F to 110F) = 581 BTU for 1 gallon of hot water. 800K BTU = 1,377 gallons of hot water – Some Guy Mar 25 '15 at 0:30

One major problem is that most propane regulators are intended for small appliances, mostly less than 75,000 BTUs/hr typical of an outdoor grill. The Rinnai V65EP can use up to 150,000, so a regulator designed for a little more than that would be the desired fit.

Shopping around, I notice many don't say what their maximum flow rate is, and of those which do, it is hard to find a "low pressure" (corresponding to less than 13.5" water column) in that range.

Here are a few I could find after several minutes searching:

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Would a 2-stage RV regulator be appropriate? amazon.com/Camco-59333-Horizontal-Propane-Regulator/dp/…. 11" WC, 160KBTU/hr. – Jay Bazuzi Aug 20 '13 at 18:33
@JayBazuzi: That looks good. Will the POL fit the tank? Will it go into the side so it can be horizontal? – wallyk Aug 20 '13 at 18:57

I am hooking up a Bosch 520 on demand to a 20# propane tank. I found this site and this product to make the connection. It satisfies the requirements for low pressure (under 14 WC), high flow (117,000 btuh).

http://www.tejassmokers.com/lowpressureregulators.htm part #108053P-60

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