Sizing a 496 for a residential load comes down to four numbers in a fixed order: inlet pressure, desired outlet pressure, and peak load — then a 20% safety margin on top. Convert the load from BTU to CFH by dividing by 1,000, add the margin, and read the 496 capacity tables at your actual inlet pressure to land on an orifice. Pick the spring for your outlet pressure, confirm the orifice's max inlet rating, and you're done.
For a typical single-family home, a 2 psi service line is usually just a few minutes of work. This guide walks the whole method, then does a worked example start to finish so you can repeat it on the next house — or the next small-commercial load that creeps up into 496 territory.
When the 496 is the right tool
The USG 496 and the USG 143 overlap in residential service, so the first question isn't how to size — it's whether the 496 is the regulator you actually want.
The 496's distinguishing feature is its 4" roll-out diaphragm, which delivers the capacity you'd normally need a 6" service diaphragm to get, in a more compact body. That, plus a wider range of body sizes (3/8" up to 1"), five outlet-pressure ranges, and a 2 psi outlet option, makes it the better pick when a load sits at the upper end of residential or pushes into light-commercial — burners, furnaces, ovens, a small multi-family set — rather than a bare-minimum single-appliance install.
The practical envelope: the 496 is the correct choice for loads up to roughly 800 CFH. Below that and you're squarely in its sweet spot. Once a load climbs past 800 CFH, you've outgrown the domestic-service class and should be looking at a larger-capacity regulator, not a bigger orifice in a 496. For the detailed head-to-head on where the line falls between the two service regulators, see the 143 vs. 496 comparison.
Inputs you need before you size
Before anyone reads a table, get these three numbers — and ask for them in this order, because each one frames the next:
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Inlet pressure. What's actually feeding the meter set? In our territory the answer is most often 2 psi, sometimes 5 or 10 psi, occasionally a higher distribution pressure. This number sets which column of the capacity table you read, and it drives capacity more than almost anything else.
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Desired outlet pressure. For standard residential service this is 7" w.c. — the 496's stock domestic set point. If the home or building is on a 2 psi delivery system, the 496 will set for that too. Outlet pressure selects your spring.
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Peak load. The total connected appliance load, in BTU/hr, which you'll convert to CFH. This is what you actually size the orifice against.
What you can usually skip for Midwest residential work: altitude and temperature corrections. At Ohio-area elevations and on standard 0.60 specific-gravity natural gas, those corrections don't move the answer enough to matter. The published tables already assume 0.60 sp. gr. gas at 60°F and 14.7 psia, which is what you're delivering. (If you're ever sizing for propane, a propane/air mix, or another non-corrosive gas, that's the exception — those need a specific-gravity correction. Standard natural gas does not.)
Step-by-step: turning a load into an orifice
Here's the repeatable method. No guessing, no "that orifice usually works."
Step 1 — Convert BTU to CFH. Take the total connected load in BTU/hr and divide by 1,000. A 240,000 BTU/hr house is a 240 CFH load. (This works because natural gas runs right around 1,000 BTU per cubic foot, so the math is clean.)
Step 2 — Add the safety margin. Multiply your CFH figure by 1.20 to build in 20% headroom. The 240 CFH load becomes a 288 CFH design load. More on why 20% — and why not more — below.
Step 3 — Confirm you're in 496 territory. Is your design load under ~800 CFH? If yes, continue. If no, stop and step up to a larger regulator.
Step 4 — Set your table coordinates. You're reading the 496 data sheet capacity table at your inlet pressure (the column) for each available orifice (the rows). Remember the table is in SCFH of 0.60 sp. gr. natural gas at 60°F and 14.7 psia — match that to your gas (for Midwest natural gas, it matches).
Step 5 — Read down to your orifice. Find the smallest orifice whose listed capacity at your inlet pressure meets or exceeds your design load. Smallest-that-works is the rule — don't reach for a bigger orifice "to be safe." Then check that orifice's maximum inlet pressure rating against your actual inlet; it has to be equal to or greater than what's feeding the set. If your inlet exceeds the orifice's max, you drop to the next smaller orifice and re-check capacity.
If reading these tables is new to you or the technician you're handing this to, our reading a USG capacity table walkthrough breaks down every column.
Worked example: a single-family home, start to finish
Say you're sizing a 496 for a new single-family residence fed off a 2 psi service line. The connected appliances:
|
Appliance |
Connected load |
|---|---|
|
Forced-air furnace |
100,000 BTU/hr |
|
Water heater |
40,000 BTU/hr |
|
Range / oven |
65,000 BTU/hr |
|
Clothes dryer |
35,000 BTU/hr |
|
Total connected load |
240,000 BTU/hr |
Convert: 240,000 ÷ 1,000 = 240 CFH.
Add margin: 240 × 1.20 = 288 CFH design load.
Check the class: 288 CFH is well under 800 CFH → the 496 is the right regulator. ✔
Set coordinates: Inlet = 2 psi. Outlet = 7" w.c. (standard residential set point). Gas is standard natural gas, so no specific-gravity, altitude, or temperature correction. ✔
Read the table: On the 2 psi inlet column, find the smallest orifice that lists at least 288 CFH. That orifice is your selection — then confirm its maximum inlet pressure is at or above 2 psi (every domestic-range orifice will be, at this inlet).
Select the spring: For a 7" w.c. outlet, pick the spring whose range on the 496 spring chart brackets 7" w.c. The regulator ships with the lightest spring suitable for the maximum outlet you specify.
That's the whole job. The only step where the exact part number comes off the chart — rather than off arithmetic you can do at your desk — is the orifice and spring selection. If you want a second set of eyes confirming the orifice code and spring color against the current data sheet before you order, that's exactly what our applications desk does.
Orifice and spring selection, once capacity is confirmed
The orifice is fixed by two constraints at once: it has to flow your design CFH at your inlet pressure, and its maximum inlet pressure rating has to cover your actual inlet. Capacity rises with inlet pressure through a given orifice, which is why the same house can need a different orifice on a 2 psi feed than on a 10 psi feed. Resist over-sizing the orifice — a larger orifice than the load calls for is a real failure mode, not a free safety buffer (next section).
The spring is fixed by your outlet pressure. The 496 offers five outlet-pressure ranges; you choose the spring whose range covers your target, whether that's a residential 7" w.c. or a 2 psi delivery point. Springs are color-coded for identification, and the spring is independent of the orifice — you can change outlet pressure later by swapping the spring without touching the orifice.
Relief comes built in. The 496 is supplied standard with an internal relief valve, and its relief performance is published on the same data sheet. If you want a refresher on how lock-up and relief setpoints relate to your outlet pressure, see the lock-up pressure explainer. For a plain-language definition of orifice terms, the orifice glossary has you covered.
Sizing for safety margin — and why over-sizing fails too
The headroom rule is simple: size to your design load plus 20%. That covers peak demand and a margin of comfort without tipping into the opposite problem.
Because both directions fail, just differently:
Under-sized is the failure everyone fears. If the regulator can't pass peak flow, outlet pressure droops under load and appliances starve — pilots drop, burners can't reach input, and on a cold morning with the furnace and water heater both calling, the house notices.
Over-sized is the quieter failure, and it's why "bigger to be safe" backfires. A regulator whose orifice is far larger than the load spends its life barely cracked open, riding near its seat at low flow. That low-flow operation tends to be unstable — the regulator can hunt or cycle, control gets sloppy, and seat wear and pressure creep become more likely over time. You paid for capacity you can't use and bought yourself a control problem.
Twenty percent is the band that gives you genuine peak headroom while keeping the regulator operating in the part of its range where it controls well. Note that summing connected load (every appliance at full input) and then adding 20% is already conservative — in real use, appliances don't all run wide-open simultaneously — so you don't need to pad beyond that.
Quick checklist
Run this top to bottom on every residential 496:
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Inlet pressure confirmed (most often 2 psi in our territory)
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Desired outlet confirmed (7" w.c. standard residential)
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Total connected load in BTU/hr summed
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BTU ÷ 1,000 = CFH
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CFH × 1.20 = design load with margin
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Design load under ~800 CFH → 496 confirmed as correct class
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Standard natural gas → no altitude/temp/sp.-gr. correction
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Smallest orifice that meets design CFH at your inlet, with max-inlet rating ≥ actual inlet
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Spring selected for outlet pressure range
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Internal relief valve accounted for in the install
If every box is checked, your 496 is sized.
Get it confirmed — and in stock — fast
Sizing a 496, or want a second set of eyes on the orifice and spring before you order?
Holland Supply stocks the USG 496 across body sizes, orifices, and springs, ready for same- or next-day shipping throughout Ohio and surrounding states. Send us your inlet pressure, outlet set point, and load, and our applications team will confirm the orifice and spring against the current capacity tables — then ship the exact configuration you need, when you need it.