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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, 2013 at 22:33
  • Why do you say that?
    – Jay Bazuzi
    Aug 21, 2013 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, 2013 at 12:41
  • 4
    You didn't say where this water heater is located, but note that in most places it's illegal to have a propane bottle indoors.
    – Mark
    Dec 25, 2016 at 18:25
  • 1
    @JayBazuzi Teenagers are notorious for using a lot of hot water. Dec 8, 2020 at 16:38

5 Answers 5

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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:

Lowes has a two stage regulator capable of up to 200,000 btus. It is inexpensive at $40.

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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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We camp at a cabin that has a Paloma so I used the following to hookup the Paloma Tankless Water Heater to the 20lb propane tank. Camco screws right into the tank and connected the Universal Kit to connect to the Paloma. Use PTFE Thread Seal Tape on all connections except the hand thread Tank Connector. Universal Kit comes with tape, but it's not labeled as rated for gas and it's white. Heard the yellow is the true gas rated tape, so I bought it separately. Test connections with soapy water. Make sure Camco vent is pointed down. Just for shower use, so did not see ice up on the tank.

Camco 2 Stage Regulator https://www.amazon.com/gp/product/B0024E6TX2/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

Universal Gas Appliance Hookup Kit https://www.amazon.com/gp/product/B01LY9SZ82/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1

Gas PTFE Thread Seal Tape https://www.amazon.com/gp/product/B000FKBXCE/ref=oh_aui_detailpage_o09_s00?ie=UTF8&psc=1

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I actually have this setup, except I have teed two 40lb tanks together. A comment above mentioned wetter space, and that is indeed the issue. I have a high BTU regulator, but the tanks simply cannot evaporate enough propane to power the water heater at full blast (157,000 BTU). It's working "fine", not the end of the world, but occasionally when the washer is filling and we are using hot water in other places it does stop working. After a few minutes the tanks thaw and we return to normal. I decided on 2x 40lb tanks because I could fill them myself and carry them inside a vehicle and would not have any kind of contract or anything.

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  • And it's worse during frigid weather, obviously.
    – SynaTree
    Dec 8, 2020 at 15:57
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Using a small portable tank will most likely create problems when using a tankless water heater. Many things come in to play with your scenario. Distance, pipe size, total BTU of ALL appliances, and tank size. Most propane tankless W/H are between 120,000-199,000 BTU's so using a small container as mentioned, your going to have a volume and flow issue in a short period of time. I've been in propane service for 25 years and almost always I install a dedicated 2nd stage regulated at the W/H. As you consume the vapor from the small tank, there isn't enough wetter space(liquid) to make up for what the W/H is consuming, so you'll get an ice build up at the bottom of the small tank

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