Boilers & Hydronic Heating in Portland, Maine

A boiler doesn't heat your house directly — it heats water, and a circulator pump pushes that water out through a loop of piping to baseboard radiators, cast-iron radiators, or radiant floor tubing, then back to be reheated. Everything downstream of the boiler is part of the system: an air-bound loop, a failing circulator, or a corroded baseboard element all show up as "the boiler isn't heating" even when the boiler itself is fine.

This is why a boiler diagnostic call is a whole-system check, not just a look at the burner.

Most Southern Maine boilers run on oil or propane, with natural gas available in parts of the service area with gas mains. Fuel choice affects both operating cost and maintenance schedule — oil systems generally need an annual cleaning and nozzle service that gas systems don't, since oil combustion leaves more soot and residue in the heat exchanger over a season.

Radiant floor systems — PEX tubing embedded in a slab or subfloor, fed by a manifold off the boiler loop — deliver some of the most even, quiet heat available in residential construction, since the whole floor becomes the radiator instead of a handful of baseboard runs. The tradeoff is response time: a radiant slab heats and cools slowly, so it's tuned for steady comfort rather than quick temperature swings.

A boiler's heat exchanger, circulator, expansion tank, and safety controls all degrade differently, and most failures we see start as a small issue — a weeping circulator seal, a slightly low system pressure, mineral buildup on the exchanger — that gets worse silently over a season rather than announcing itself. Annual service catches those before they become a mid-January no-heat call, and it's also required to keep most manufacturer warranties valid.

Weil-McLain

Weil-McLain's condensing residential line goes by Evergreen Pro, and it scales from a 110,000 Btu/hr input up to 399,000 across five sizes. AHRI has certified the two smallest units in that lineup, the 110 and 155, at 95.0% and 95.1% AFUE respectively — numbers straight from Weil-McLain's own manual. One installation detail matters more than the efficiency rating for retrofits: Evergreen is a Category IV appliance that has to vent through 3-inch PVC, so an existing masonry chimney is off the table.

Burnham (U.S. Boiler Company)

Burnham is a boiler brand of U.S. Boiler Company. Its flagship condensing line, the Alpine, is rated at 95% AFUE across all six sizes (80,000 to 399,000 Btu/hr input) per the manufacturer's data sheet, and vents through PVC or CPVC with an adapter kit. U.S. Boiler still sells cast-iron oil boilers for homes staying on oil — the EMP and MPO-IQ lines are rated at 87% AFUE, and the MegaSteam steam boiler at 86%.

Buderus (now Bosch)

Buderus boilers are still common in older Maine basements, but Bosch — which owns the Buderus brand — now lists Buderus residential boilers, including the Logamax plus GB142, on its own discontinued-products page and sells its current condensing lineup under the Bosch name. The GB142's service manual rates thermal efficiency at 88% at full firing rate and up to 97% at part load with a low return-water temperature. That's a different test than AFUE, but it shows how much a condensing boiler's real efficiency depends on the water temperature it's actually piped to run at. The GB142 vents through PVC or CPVC.

Navien

NCB-H is Navien's combi play — one box handles both space heating and the house's hot water, sized from 11,000 up to 150,000 Btu/hr of heating input across five models. Every size in that range tests to 95.0% AFUE under DOE procedures, per Navien's installation manual. Venting runs the same course as the other condensing units here: Category IV, 2- or 3-inch PVC, CPVC, or approved polypropylene.

Viessmann

Every model in Viessmann's Vitodens 100-W range — the company's entry point for residential condensing boilers — is rated at 95% AFUE, spanning roughly 8,500 to 199,000 Btu/hr input. One convenience worth knowing about: the control lets a technician switch the unit between natural gas and propane without a separate conversion kit, per Viessmann's own product documentation.