Hello Heat Pump, Goodbye 2 Tons of CO2 per Year

by Angela Kantola

Hooray – we now have a ducted, air-source, cold-climate heat pump – and it works great! We knew our ~27-year-old 90% efficient gas furnace wouldn’t last forever, so we’ve been planning to convert to a heat pump as part of electrifying our home. Talking to heat pump owners of homes on the Metro Green Homes Tour was immensely helpful (you can see video tours of homes on those tours here.)

We live in the foothills above Littleton at 7,300’ elevation, so our main need is for heating. Cooling will also be helpful on increasingly hot summer days. We started this energy upgrade with an energy audit from Xcel (our natural gas provider). The blower door test measured our home’s airtightness at a fairly leaky 9.96 ACH50. Our auditor recommended we tighten our home’s envelope by sealing and insulating our crawl spaces and attic and insulating our attic hatch.

We began talking with recommended heat pump and insulation contractors, and scheduled insulation and air sealing before heat pump installation. We asked our potential heat pump contractors to carefully consider the unique features of our home and energy use as they prepared bids.

●      Our house is not large (1,581sf).

●      We have an efficient woodstove we enjoy using (burning ~1.5 cords of wood/year).

●      We’ve used only ~314 therms of natural gas/year to heat our home (even that emits ~2 metric tons of greenhouse gases/year).

●      Our house faces due south and has some passive solar features.

●      We previously upgraded doors and windows to high-quality double and triple pane.

Bids from three competent heat pump specialists were fairly close in cost system size ranging from 2.5-ton to 4-ton. We had follow-up discussions with two of the contractors to discuss available units and ideal size. (The more I learned about heat pumps, the more convinced I became that they can often be oversized.) The contractor we selected agreed that in our use case, a 2-ton system made good sense, would run more efficiently and quietly than a 2.5-ton system, and provide almost identical output. The caveat is that this system is not sized to cover our entire heat load at 0℉ outdoor temperature, but our cozy woodstove provides the backup.

We'll monitor our increased electricity use as we operate the heat pump this winter, then consider whether we want to add capacity (or battery) to our 6.5kW rooftop PV system.

Additional note: we knew our radon levels of ~5 pCi/L were of some concern, so we began monitoring with an AirThings monitor over several months beginning last April. Encapsulating our crawl spaces had the potential to increase radon levels, thus we’d intentionally had a radon-ready vapor barrier installed. Sure enough, radon levels more than doubled after the crawl space work. We subsequently had a quiet, efficient radon mitigation system installed and the levels quickly dropped below safe levels.

Angela will showcase this conversion at the November 3rd Heat Pump Panel at the Golden Community Center!

Heat Pump Air Handler

Former Rheem gas furnace

Crawl Space sealing and insulation