I have a small stove with a propane conversion kit and a 3gpm propane tankless water heater. This is for a small MIL suite ~650 sqft. Both the stove and the water heater are on the same exterior wall, about 6ft apart. The wall has no windows or other openings. I want to place 2 20lb BBQ tanks outside on that wall. I've been searching for information about connecting a changeover valve like used in RVs to them. From there, a short run of black pipe, through the wall to street elbows and a shut-off valve at each appliance. Both appliances have 1/2" connections. I can't seem to find specific information about connecting the tanks to the black pipe. What do I use? I am going to have this pressure tested and inspected after I'm done.

  • 40lbs of propane isn't a whole lot of propane, especially for a tankless heater! – ThreePhaseEel Sep 19 '16 at 0:23
  • I did the calculation on the tankless alone. 430k BTU tank and 75k BTU tankless (430000/75000/.25). A single tank should last about 23 days given a 15 minute shower once a day. I do not expect this to be used heavily. Some reviewers said they get between 45 and 60 days on a 20lb tank. The 75k BTU/hr is the max 45 degree rise at 3.4 GPM. A shower uses 2.5 GPM and we have between 62-72 degree water year round. – kyle Sep 19 '16 at 12:26
  • Ah -- good that you ran the numbers -- the duty cycle of your operation is what makes this different from the previous cases I've seen on this Stack. – ThreePhaseEel Sep 19 '16 at 23:11
  • After more than a year of running on BBQ tanks, I can say that this has worked out well. The propane powers both a stove and the tankless. Washing dishes, cooking, and showering is about a month per tank. – kyle Dec 12 '17 at 5:00

What I ended up getting was a hose with a regulator. On the other end was a 3/8" flare female. I found a 3/8" flare male to 1/2" MIP (Male iron pipe). I used a 1/2" coupling to a 3" nipple to a tee. From there it went to each of the 1/2" nipples through the wall, to a street elbow, and finally to a gas shutoff valve. This is the basic setup now. I'll have to order a changeover for the 2nd tank.

street elbow => shutoff         street elbow => shutoff
|              ---------        |
|                wall           |
|              ---------        |
              1/2" coupling
        3/8" male flare to 1/2" MIP
Regulator with hose 5/8" female to 3/8" female
              propane tank
| improve this answer | |

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