Furnace Installation & Replacement in Boulder

Mapleton Hill has about 500 homes, most built before 1910, and many were converted from coal or gravity heat decades ago. Furnaces there are often in cramped basements with venting into old masonry chimneys. Martin Acres, from the 1950s, has smaller ranches with furnaces that are frequently on their third generation. Table Mesa and Gunbarrel homes from the 1960s through the 1980s often still have duct layouts built for much larger furnaces than they need today.

Boulder's elevation calls for about a 21% derate, so a 60,000 Btu/h input furnace runs at roughly 47,000 here once it is set up for altitude. Older homes that have had insulation and window upgrades often need far less heat than the original equipment supplied. A Manual J load calculation shows that, and it matters even more if you are considering a heat pump, since heat pumps are sized to the load rather than the old furnace.

If a gas furnace is allowed, it must meet the 14 ng/J NOx limit or the current ENERGY STAR version (97% AFUE since July 31, 2026). An ultra-low NOx 80% furnace can sometimes keep a lined chimney vent in an older house. A condensing furnace needs PVC venting and a drain, and the water heater left in the old chimney needs its own properly sized vent. SWEEP's 2023 analysis noted some ultra-low NOx furnaces need a high-altitude conversion kit. See our NOx rules guide for the background.

The city's recent rebate lists have excluded gas furnaces, and in 2026 the county's EnergySmart rebates go only to income-qualified homeowners. Heat pumps have more support: Colorado's $1,000 air-source heat pump credit, Power Ahead Colorado's $1,500 for cold-climate units, and Xcel heat pump rebates, which changed October 1, 2026 and should be confirmed with Xcel. The federal 25C credit ended after 2025.

For homes with good ductwork, a dual-fuel system keeps a gas furnace for the coldest hours. For Mapleton Hill houses with limited duct space, ductless mini-splits are often the cleaner fit.