The Miller Homestead: Incremental Improvements in Home Energy Efficiency
Chasing Energy Efficiency and Electrification in a New England Home – Converting from Natural Gas to Heat Pumps
By: Nathan Miller, Lead Energy Analyst & Mechanical Engineer
Growing up as somewhat of a misfit in rural Maine, I always assumed I’d “escape” my native state and never look back. I only applied to west-coast colleges, and upon graduating from the University of Washington, I happily accepted a job in the local buildings design industry. However, after about 15 glorious years in Seattle, I slowly came to the realization that Maine, with its four “proper” seasons, natural beauty, and, most importantly, family connections, wasn’t such a bad place to live after all. My family prepped for our great move back East.
My wife took on the challenge of finding us a new home in a tight housing market, and we eventually purchased a classic Victorian house in Portland, Maine (aka- “real” Portland, sorry, Oregon). We knew from the get-go that there would be many opportunities to improve the energy efficiency in the house as it was originally built in approximately 1870 and has only seen modest updates since (see Key Improvements Since Purchase at the bottom).
Additionally, as-purchased, the house was entirely reliant on natural gas for both space heating and domestic hot water, which, while economically and environmentally superior to the heating oil systems common in Maine homes, also saddled us with a significant carbon footprint due to Maine’s heating-dominated climate.
After swapping out the domestic hot water heater for a tank-style heat pump early on in our ownership, by 2020, we realized that the mid-2000s-era natural gas boiler that fed hot water to our cast-iron radiators was on its last legs, and that we should develop a replacement plan BEFORE it went belly up in the middle of the heating season. Ultimately, we decided to switch from gas boiler to split-system-heat-pumps and have NEARLY kicked the natural gas habit (we still have a gas range, but converting to electric induction is on the to-do list).
In this blog post, I explore how some of the expectations and concerns we had regarding heat pumps compared to our lived reality.
Expectation: Heat pumps are more energy efficient than gas boilers.
Reality: Unequivocally we use less household energy (aka- site energy) with the heat pumps compared to the natural gas boiler. The blue line in the chart below is our metered energy consumption at our house (for both electricity and gas, converted to common units of Mega-BTU). The light green line projects what our total energy use would have been if we’d replaced the old natural gas boiler with a similar contemporary boiler.
Expectation: Adding cooling will significantly offset the improvement in heating efficiency.
Reality: We definitely do more cooling now that we have whole-house air-conditioning from the heat pumps (vs previously, we had a few window-AC units), but the modest increase in summer cooling is dwarfed by the energy savings in the heating season thanks to the heat pumps.
Expectation: Heat pumps will save you money to run compared to boilers.
Reality: Well, it’s complicated, but with standard Maine utility rates it appears the answer is no, gas heating is currently cheaper (despite being less efficient).
However, Maine is encouraging the use of heat pumps by offering a special utility rate that reduces the electricity cost during the heating season but increases the electricity cost during the cooling season. This rate is only available to homes with heat pumps as their primary means of heating
Expectation: Heat pumps will result in a lower carbon footprint.
Reality: New England has a relatively “clean” electricity grid from a carbon emissions standpoint, so switching to heat pumps drastically reduces net emissions in our household. We also opt-in to purchasing 100% “green” power, meaning the supplier must acquire Renewable Energy Certificates in the amount to offset our electricity emissions. If you are willing to believe the REC market is legit, then our household essentially operates with almost no net carbon emissions.
Expectation: Heat pumps can’t keep up on a really cold night, and your house won’t be as comfortable.
Reality: This is a fascinating and hard-to-quantify metric, and I wish I could give a definitive answer, but I’ll have to settle for a qualitative comparison table (who doesn’t love that?):
Check mark indicates that system is the greater option for that category.
Overall, I am quite happy with the operation of the heat pump system in my home. I’m still looking for ways to improve the overall efficiency, and gradual improvements to my insulation and air-leakage will also help with the comfort issues. There is no doubt that my wife misses being able to snuggle up next to a hot radiator and just bliss out, and since we never removed the hydronic piping and radiator from my house, I am intrigued by the developing market of “drop in” Air-to-water-heat-pumps that could replace a gas boiler. That would be a much simpler retrofit for an old home than a full split-system install.
I hope you found this analysis interesting, and if you have any questions, feel free to send an email to firstname.lastname@example.org.
Details as Purchased in 2014:
- Single family home in Portland Maine. 4 BR, 1 bath, 2400 SF, Victorian built in the 1870s.
- Uninsulated wood framed walls with single pane wood framed windows
- Unheated, unfinished attic with haphazard insulation- mix of vermiculite (asbestos) and fiberglass batts laid down between rafters
- Unheated, unfinished basement with spotty adhered rigid insulation
- Early 2000’s natural gas boiler (Munchkin condensing boiler) for space hydronic space heating with cast-iron radiators
- Late 1990’s natural gas hot water heater
- Abandoned in place oil tank from previous boiler, accommodations for coal boiler, open fireplaces
- Knob and tube electrical wiring
Key Improvements Since Purchase:
- Triple Pane Vinyl Window replacement (2014)
- Modern electrical system (2015) + panel upgrade (2021)
- AO Smith Tank-Style Heat Pump Hot Water Heater (2017)
- Community Solar Purchase (2020)
- Multi-head Split System Heat Pumps (2021)
- Spray in cellulose attic insulation (2023)