Three tiers dominate whole-home quotes in this market: 18kW, 22kW, and 26kW. The box prices step up predictably. The installed totals don’t — because stepping up a tier can quietly redraw three other line items on the seven-item invoice, while four more barely notice the change. We don’t post dollar ranges here; what we can map precisely is which numbers move when you move up.
What steps up when the tier steps up?
The pad. A bigger unit wants a bigger footprint, sized per its install manual. Concrete is cheap enough that this rarely decides anything, but it’s real.
The gas line. A larger engine breathes more fuel, and fuel arrives through pipe. Each tier’s required line diameter comes from the install manual for that unit — and a bigger diameter can mean a new run rather than a reused one, which is trench work, which is money. On a marginal meter, the bigger tier can also trigger the upgrade conversation the smaller tier never starts.
The transfer switch. The ATS — the box that moves your house between grid and generator power — is specced to your electrical service and the unit’s output, commonly a 200-amp whole-house switch. Tier packages sometimes bundle different switches, and a switch swap ripples into the electrical line item.
What barely notices the tier?
Permits are jurisdiction-priced, not kilowatt-priced. Commissioning is the same visit with the same checklist. Electrical work scales with your panel and the pad-to-panel distance far more than with unit size. And the pad, as noted, moves by feet, not by multiples.
That’s four of seven line items roughly flat across tiers. The practical consequence: the installed-cost gap between tiers is mostly the unit-price gap plus fuel-side surprises — and the fuel side is house-specific, which is why tier pricing off a website (any website, including this one eventually) still isn’t a quote.
So which tier should you price first?
The one your nameplates point to — not the one the brochure leads with. The measured answer sometimes lands a tier below the pitch, especially with load management in the design, and the savings then compound: smaller unit, possibly thinner gas line, possibly no meter upgrade.
Then pressure-test the step-up honestly: if the bigger tier buys margin you’ll actually use — a second HVAC, a shop, medical equipment — it can earn its price. If it buys “just in case” for a stack that never happens, the worth-it math says put the difference elsewhere. And if a payment plan is what makes either tier feel reachable, read the financing checklist before anyone runs your credit.