The answer — one pick, priced
Get the
Rheem RTEX‑18
no budget ceiling
The proven 1–2 bath workhorse across 7 expert sources — 18 kW and 4.4 GPM on just two 40A breakers, the simplest whole-house install on this list.
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Fit ledger — need → measured evidence
■ The catch — co-equal billing, always
It is an 18 kW unit. The 4.4 GPM rating is quoted at a modest temperature rise; where winter inlet water drops under 45°F it loses a large share of that flow, and it will not run two showers at once. For multi-fixture capacity in a cold climate, 27–36 kW is the floor.
Dealbreaker? Runner-up №1 is the 27 kW cold-climate floor ↓
■ Every product has a catch. Verdicts that hide it are how bad buys happen.
Runners-up — if your needs differ
Adjacent verdicts — same method
Traps — this verdict avoids
Phantom GPM
Headline flow rates are quoted at a modest temperature rise. A unit rated 7.5 GPM at a 35°F rise can deliver under 4 GPM at a 70°F rise — a heater that runs four showers in Florida may not run one in Minnesota. Size by your winter inlet temperature, never by the box.
The panel bill the price hides
A 36 kW whole-house unit draws 150A — three 50A 240V breakers — and 27–36 kW units routinely force a 200A panel or service upgrade costing $1,000–$3,000+ on top of the heater.
The tax credit is gone
The federal 25C credit (30% of cost, up to $600) applied only to property placed in service on or before 2025-12-31. A 2026 install earns no federal credit — budget the full sticker and check state/utility rebates instead.
Provenance — 7 sources, dated
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