Furnace Installation & Replacement — Duluth, Superior & the Northland

Sizing: the thing most Twin Ports furnaces get wrong

The majority of furnaces we replace are oversized — frequently by 30–50%. It happens because the easy way to size a furnace is to read the old one's nameplate and match it, and that error compounds every time the furnace is replaced. Meanwhile the house has probably had windows, insulation or air-sealing done since 1985.

An oversized furnace satisfies the thermostat fast, shuts off, and repeats — short cycling. You get temperature swings, cold rooms far from the furnace, more wear on the ignition components, and worse humidity control. In a −20°F climate the instinct is 'bigger is safer', and it is exactly backwards.

We run a Manual J load calculation on the actual house: square footage, orientation, window area and type, insulation levels, measured or estimated infiltration, and the real ASHRAE design temperature for the Twin Ports rather than a national average. Then we size to that, with a sensible margin, and we show you the calculation.

80% or 96%? The honest answer depends on your house

A 96%+ condensing furnace burns roughly 16% less gas than an 80% unit for the same heat. Over a 9,000+ HDD heating season that is real money, and it is why we recommend condensing equipment in most cases.

But it is not free. A condensing furnace needs PVC intake and exhaust through a sidewall, a condensate drain that will not freeze, and — if it was sharing a chimney with a natural-draft water heater — that chimney now needs a liner or the water heater needs to change too, because an orphaned water heater in an oversized masonry flue is a genuine backdrafting hazard. Those costs are real and we put them in the quote rather than discovering them on install day.

Where an 80% unit still makes sense: a house with no practical sidewall route, a rental you are selling within a few years, or a chimney-vented setup where converting the whole vent system would cost more than the fuel savings recover. We will say so.

Rebates and credits — we do the paperwork

This service area sits across three different utility rebate regimes and most homeowners never claim what they are owed. Duluth natural gas customers go through Comfort Systems. Natural gas outside Duluth is usually Minnesota Energy Resources. Electric heat pumps and ECM equipment on the Minnesota side go through Minnesota Power's Power of One® Home program. Everything in Superior and the rest of Wisconsin goes through Focus on Energy.

We identify which programs your address and equipment qualify for, install to the efficiency tier that actually earns the rebate, and file the paperwork for you. The federal 25C Energy Efficient Home Improvement Credit may also apply — we give you the AHRI certificate and model numbers your tax preparer will ask for.

What a proper install includes

Permit pulled where the jurisdiction requires it. Old unit and refrigerant handled legally. New furnace set level on a proper base with service clearance preserved. Gas line sized and leak-tested. Venting run to the manufacturer's spec with correct slope and termination clearances — not the shortest path. Condensate routed somewhere that will not freeze. Ductwork transitions sealed with mastic, not tape.

Then commissioning, which is the step that gets skipped: static pressure measured, gas pressure clocked at the meter, temperature rise verified inside the nameplate range, combustion analysed, safeties proven, and the blower speed actually set for your duct system. A furnace installed but not commissioned is a furnace running somewhere other than where the engineer intended. We leave you the numbers in writing.