Heat Pump Check-in — 2024
Way back in 2021 I finally found an installer who would install a ground source heat pump with no fossil fuel backup. It only took 5 years to find this contractor, in part because I hadn’t been looking at the commercial installers and the residential installers all had incentives from the utility to install gas. The residential units were also too small for my home, the volume of sales was just too small to justify larger units in our (US) market. Without fail the available incentives, rebates, experience, whatever, all led to a natural gas furnace with a novelty heat-pump tacked on. I was determined, and so after 5 years of searching I installed a ‘light commercial’ unit sized to replace the existing furnace and air conditioning for my home, with a water cutoff to feed the heat pump hot water heater. This install and immediate experience was documented in August 2021, now 3 years later this piece follows-up to tell the story so far.
The Water Furnace heat pump has been rock solid throughout. It tested out at COP = 4.99. The heat pump hot water heater is ok, maybe? Frequently trips its own circuits in fall and spring, the temperature change causes it to vapor lock itself (speculating, it was the same brand it replaced but reliability is not in the same class). These components replaced a 21 year old furnace and 26 year old hot water heater — both natural gas fed.
The immediate system performance resulted in a 20% reduced energy consumption, despite a 90% increase in electricity consumption. This translated into a savings of about $350 in the first year… nothing against the cost of the system. Things look worse now, my energy bill has increased 40% over the last 4 years! But hidden in that is the increase in Natural Gas rates of 60% and electricity by 40%… so yeah, I’m saving even more than I would in the counterfactual where I kept on with a flakey furnace, AC, and water heating system. Only the water heater was reliable, with both the furnace and AC breaking down under extreme conditions.
And about extreme conditions! The 2021 heat dome arrived a month after install and the system performed admirably. It has kept up through 3 winters and summers without flinching. We went from unreliable temperature to rock-solid stability year over year. Super happy with the performance of the heat pump!
During winter the lower temperature of the exchange field is visible at first and last snow, that few degrees difference leaves clear stripes — despite the 3 and 6' depths of the circulation lines. In coldest winter (after a week in the mid-20s F) the inlet temp was 36F and the outflow temp 31F, that 5F delta T still providing ample exchange power for the heat pump to function.
Unfortunately, the installation didn’t go as smoothly as we’d hoped — we knew we nicked the drain field line during trenching and thought we’d repaired it. There was another break upstream at a joint that came apart the following spring. 12 yards of rock and soil in hand-trenched French drains later, we finally realized the soggy spot was due to a drain field leak and got that fixed. Today the exchange loops are settling, so the trench lines need a bit of a top-up, but otherwise it remains out of sight and out of mind.
Looking over years of utility usage and bills, it is hard to make out all the nuance of what has happened over the last 9 years. The drop in natural gas consumption is the easy and obvious bit, 10 Tons of annual CO₂ emissions reduced as a result of the installation. Super happy with that. Immediately after the install the total energy consumption dropped by 20%, this has held over time — even as we use the house more heavily in a post-pandemic working from home world.
Cost wise, that’s not so easy to understand. In the first year costs were down year over year in every month but one, and down by $350 in total. Not great against that investment, but the 10T CO₂ sure stands out here. Looking over the years since install… my bill is up 40%. That’s a lot more expense than before the install. This hides the cost climb in natural gas — 60% over the same time. I’m saving even more now against the counterfactual of continuing to burn methane. But this was never going to be an economic decision with a known payback — that’s not sending a price signal. It improved quality of life and does less damage to the environment— and both are unpriced advantages of the transition.
The pandemic also occurred during this time, so instead of 5 people rarely being at home we ended up here all the time for several years. I also transitioned from working in the office to working full time at home, leading to about 8 computers being shifted into the home full time (across the 5 of us — remote learning was a thing too), a non-zero contribution to increased power consumption. All in all it is challenging to isolate changes in consumption to individual components or effects, but again the nearly full elimination of natural gas consumption stands out as clear and obvious.
I do still have a natural gas generator, and when the power is out I lose the heat pump but keep the water heater. This strange configuration is due to the panel space required by the backup strip heaters and the unfamiliarity of what this system was for the electricians setting it up. The generator didn’t have the headroom for everything, and the heat pump with 180A across 3 circuits basically declared itself too big a load to manage. In hindsight I’d rework the panel to circuit share several of those loads — the strip heaters (2x 60A) have never been used and they’d be a great option to share a circuit with the hot water heater (or the legacy jacuzzi tub that also has rarely been used — mostly by children).
The panel headroom is also why the in-house EV charger was disconnected and why we couldn’t replace the range top in the kitchen. With circuit sharing or a panel battery we’d be able to support all the things, but 4 years ago no one knew to attempt any of that — even if the codes would allow it.
Speaking of that: the codes, incentives, and tradespeople required to support a transition off of gas just don’t exist yet (and aren’t aligned). Just last year I was unable to get a pure heat pump replacement for my mother’s furnace — she ended up with a new natural gas furnace to pair with her heat pump. No contractor would install without it. That natural gas unit has been nothing but trouble, of course, and we can see the hazardous air quality that comes with a natural gas burner inside the building envelope. But that’s what the utility is still paying for, and the installers know how to collect those rebates.
My utility also continually points out that I use more electricity than my neighbors. They do the finger wagging because they report out on electricity consumption but never report or include the natural gas consumption — and of course my reduction in total energy consumption came with a dramatic increase in electricity consumption.
The folks who read and reply to my complaints about this aren’t empowered to do anything about it, they also recognize that it is a bit of a bad comparison. This is one of the background biases towards gas consumption, no amount of gas consumption shows up during the conservation events or monthly neighborhood comparisons — It should be the only thing we’re tracking until that goes to 0 then we can work through the efficiency track.
Anyway, next steps should be to finish replacing windows and insulating the home (cold spots on external walls in winter are obvious to touch, all the original double pane 36 year old windows failed and only half have been replaced). Actually rooting out the natural gas cooktop is way down the climate, health, or ROI scale. I pay for $30 of natural gas each year (17 days of power outages last year) and $150 for the connection fees for the gas. It’ll cost about $5k to swap out that range because it forces panel work (or a yet to be released induction cooktop with 120V service and built in battery). I should clean and seal the ducts too, but there be spiders down there in the crawlspace (we did that insulation on moving in). Older homes have a lot of retrofit work required, it can be a lot to bring up to code especially when you are ahead of the incentives (I love the incentives, please help more people do what I’ve already done!). None of this is easy enough or aligned enough with the trades, utilities, or incentives to happen on its own right now, too much time and cash has to come into it from those who are suffering the consequences the system made decades before they moved in.
To sum up:
- Dropping Gas furnace for a heat pump: 10/10 would recommend.
- Dropping Gas Hot Water Heater for heat pump: 8/10 wouldn’t recommend a brand’s first gen model — they should have it sorted by now.
- 10 tons of annual emissions avoidance from a long-lived piece of home infrastructure = priceless.
