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Natural Gas To Propane Conversion

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I could use some help from any of the HVAC people that may be on board?

I'm converting a NG pizza oven to LP.  I have the replacement nozzles and the conversion kit for the Robertshaw gas valve. Replacing the hard parts look relatively easy. My question is what should the inlet and manifold pressures be? The spec plate on the oven, only gives NG pressures; as in 7" WC inlet and 3.5" manifold.  From my research the inlet pressure for propane seems to be 11" - 13" WC; but getting mixed info on manifold pressure? Some techs are telling me half the inlet pressure (like NG) and others are saying 8"-10". One last question, do you check pressures static or with the burners fired? I assume fired but every time I assume something; I turn out to be the ass in the equation. LOL



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You should consult with the manufacturer. If they make the same appliance in propane they will have the info. Failing that, orifice size and manifold pressure rely on each other. So I think whoever sized the orifices should be able to tell you manifold pressure. It is all based on number of burners and appliance input. There are tables in the B149.2 for orifice sizing.

10’wc is not uncommon manifold pressure for propane.

And yes, pressure is with appliance operating. 

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It actually all hinges on BTU output. 

Orifice is according to supply pressure required for specified BTU output. 

Manufacturer's spec's should be followed. 

I've been involved with TSSA... on natural/propane gas issues.. not nice. 

Having said that.... there's lots of stuff that is done and works fine. 

There's maybe someone at south end of your building.... some get service done by you. 

Check manufacture spec's.

That's my (official) stance.

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