Sizing a Gas Line for a Whole-House Generator in Chicago
A whole-house standby generator is one of the best upgrades a Chicago home can have — the storms and grid stress that knock out power don’t care that your sump pump and furnace need to keep running. But here’s the thing the generator brochure glosses over: the generator is only as good as the gas line feeding it, and a standby unit is one of the largest gas loads you can add to a house. Get the line sizing wrong and the generator starves, runs rough, throws faults, or won’t carry its rated load right when you need it most — in the middle of the outage it was bought to solve. This is a load-math problem before it’s a plumbing problem, and it’s the part that separates a generator that works from one that disappoints.
Why a Generator Is Different From Every Other Appliance
Most gas appliances you add to a house are modest, intermittent loads — a range burns for an hour, a dryer cycles, a water heater sips. A whole-house standby generator is a different beast entirely: it’s a large, sustained draw that can rival the combined demand of much of the rest of your gas equipment, and it pulls that load continuously for as long as the outage lasts — potentially hours or days. That changes the sizing question fundamentally. It’s not “can the line handle one more appliance”; it’s “can the supply deliver a major new sustained load on top of everything else that might be running — the furnace, the water heater, the range — without the pressure sagging below what any of them needs.” During a winter outage, that’s exactly the scenario: the generator kicks on and the furnace is running hard and someone’s cooking. If the gas supply can’t feed all of it at once, something starves — and a starved generator is the worst thing to discover mid-blizzard.
The Three Factors That Decide the Line Size
- ✓ The generator’s BTU demand. Bigger units (measured in kilowatts of electrical output) pull proportionally more gas. The unit’s spec sheet gives the BTU/hr requirement — the starting number for the whole calculation.
- ✓ The distance from the meter. Gas pressure drops over distance, so a long run to a generator at the far side of the house needs a larger-diameter pipe than a short one to deliver the same BTUs. This is where DIY guesses fail most often — they size for the appliance but ignore the run length.
- ✓ The home’s existing total load. The generator doesn’t run in isolation. The calculation has to sum everything that could draw at once and confirm the supply — and the meter itself — can carry the total. This is what usually triggers a supply or meter upsize.
Why the Meter Often Has to Grow Too
Here’s the piece that surprises homeowners: sometimes the line from the meter to the generator is the easy part, and the real bottleneck is upstream — the meter and the supply feeding the whole house simply weren’t sized for a load this big. A standard residential meter provisioned for a furnace, water heater, range, and dryer may not have the headroom to add a large generator’s sustained draw. When that’s the case, the fix involves coordinating with Peoples Gas to upsize the meter or supply so the house’s total provisioned capacity can carry the new load. That coordination is a normal, expected part of a generator installation done right, and it’s exactly the step a general handyman or an electrician-only generator installer isn’t equipped to handle. The gas side of a standby generator is a licensed-gas-fitter job precisely because it so often reaches back to the meter and the utility, not just the appliance.
What a Properly Done Generator Line Includes
| Component | What it involves |
|---|---|
| Load calculation | Generator BTU demand + run distance + full existing household load, summed and checked against supply capacity |
| Dedicated, sized line | Correct-diameter pipe for the load and distance — not tapped off an existing undersized branch |
| Supply / meter upsize (if needed) | Coordinated with Peoples Gas when total load exceeds provisioned capacity |
| Permit | Filed before pipe is cut (~$75), like all Chicago gas work |
| Pressure test + affidavit | Proves the new line tight before the generator is commissioned |
| Coordination with the electrician | The gas side and the electrical side of a generator install are separate trades — done in sequence |
A generator gas line typically runs $2,000–$5,000, with the range driven mostly by the run distance and whether a supply or meter upsize is required. That’s the honest cost of a generator that carries its rated load through a multi-day winter outage — the number to be wary of is the suspiciously low one that almost always means the load math got skipped.
Generator Gas Line Questions, Answered Straight
Can I just connect my new generator to my existing gas line?
Usually not without checking — a standby generator is one of the largest gas loads you can add, and tapping it onto an existing undersized line is exactly how generators end up starving, running rough, or faulting under load. It needs a load calculation and almost always a dedicated, properly sized line. Sometimes the existing supply can carry it; you find that out by doing the math, not by assuming.
How much does a gas line for a whole-house generator cost in Chicago?
Typically $2,000–$5,000, driven mostly by the distance from the meter and whether the supply or meter needs upsizing to carry the new load. It’s a bigger job than a normal appliance line because of the generator’s size and the frequent need to coordinate an upsize with Peoples Gas. A very low quote usually means the load calculation was skipped.
Why would the gas meter need to be upgraded for a generator?
Because the generator’s sustained draw, added to everything else in the house, can exceed what a standard residential meter was provisioned to deliver. When the total load outgrows the meter’s capacity, upsizing the meter or supply (coordinated with Peoples Gas) is the fix. It’s a normal part of a generator install done right, and it’s why the gas side needs a licensed fitter, not just the generator’s electrician.
My generator runs but seems to struggle under heavy load. Is that the gas line?
Very possibly — a generator that starts fine but falters when it has to carry real load (or when the furnace and other appliances are also running) is the classic signature of an undersized or starved gas supply. It’s worth having the line and the total household load evaluated. A generator that can’t carry its rating during an outage isn’t doing the one job it was bought for.
Does the distance from the meter to the generator really matter that much?
A lot — gas pressure drops over distance, so a generator at the far end of the house needs a larger-diameter line than a close one to deliver the same BTUs. Sizing for the generator’s demand while ignoring the run length is one of the most common ways generator lines come out undersized. Both factors go into the calculation together.
Do you handle the whole generator install or just the gas?
The gas side — the sized line, any needed supply or meter upsize coordinated with Peoples Gas, permit, and pressure test — which is a distinct trade from the electrical side (transfer switch, wiring) that a generator electrician handles. The two are done in coordination. If you’re planning a standby generator, bring me in for the gas load calculation early, before the unit’s location is locked, so the run can be sized sensibly. See our outdoor gas installation page.
Planning a Standby Generator? Get the Gas Load Math Right First.
Proper load calculation, dedicated sized line, meter-upsize coordination with Peoples Gas, permit, and pressure test — so your generator carries its load when the grid quits. Same-day across Chicago.
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This guide is general information for Chicago homeowners, not a substitute for an on-site load calculation by a licensed professional. If you smell gas, prioritize safety: leave and call 911 and Peoples Gas (1-866-556-6002).