LP gas at high altitude: select orifice from drill size table

What is going on

Propane has a consistent heating value, so picking an orifice at altitude is more of a table lookup than a calculation. The catch, which people trip on, is that this furnace uses 10 in W.C. at the orifice, not the 11 in W.C. used in the NFGC LP chart. So do not use the NFGC LP orifice sizes. You reduce sea level input by 4 percent per 1,000 ft, then pick the orifice from the LP drill size table. The table applies to 90 Plus models only.

Likely causes

• LP furnace going in at high elevation
• Orifice table confusion between the NFGC chart and the furnace's own table
• Ordering orifices for a conversion kit
• After a move or a change in installation altitude

Check in this order

1. Find the altitude band for the installation
2. Read the reduced input per burner for that band from the LP orifice drill size table
3. Select the drill size listed for that band
4. Order the orifice using the part number format 62-22175-(drill size). Example: #60 drill is 62-22175-60; 1.10 mm is 62-22175-90
5. Drill sizes available are 39 through 64, plus metric 1.10 mm (-90)
6. Do not use the NFGC LP orifice sizes, they assume 11 in W.C.
7. After fitting, verify manifold pressure and flame

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