What Do We Need More: Insulation or Heatpumpification?

Actually, we need a lot of both. The question is, in what order.

Heat pumps with wind and solar
The future we want: heat pumps powered by renewables.

ewg3D / Getty Images

"Electrify Everything!" has been a popular mantra recently, thanks to the writings of inventor and author Saul Griffith, along with environmental writer David Roberts' fist pumps for heat pumps. The idea is that if we switch from gas furnaces and boilers to heat pumps running on clean electricity, voilà!—no carbon emissions. No need for expensive and time-consuming renovations either. With low-carbon electricity, who cares how much you use?

As I have tried to explain before, the utilities supplying the electricity care. They have to be there to meet the peak daily and seasonal loads, and the way to reduce peak loads is with building efficiency. That's why I continued to say "fabric first!" Back in 2018, I wrote "Reduce Demand. Clean Up Electricity. Electrify Everything." I have also promoted deep retrofits and energiesprong, which cut energy consumption for heating and cooling to almost Passivhaus levels, but have noted they are disruptive, expensive, and time-consuming. There is no question that the availability of efficient and affordable air source heat pumps (ASHPs) has changed the equation.

In the United Kingdom and Ireland, they are wrestling with the same issues. Scientist and consultant Richard Erskine recently wrote, "Insulate Britain! Yes, but by how much?" about this equation. The title is an allusion to the Insulate Britain activists we covered here, asking:

"Some experts say we need to insulate our homes so well they will hardly need any heating! Others say we need to get off gas as fast as possible by installing heat pumps. Who is right?"

Erskine suggests that many of us with the "fabric first!" preoccupation are stuck in the past, and have to do a quick rethink.

"The 'retrofit community' generally have established an article of faith that 'deep retrofit' is essential. This is a belief that has very deep roots and predates concerns about the climate emergency. Key organisations in the public and private sector promote this belief. Their motivation is to create greater comfort in homes and to lower heating bills, and who can argue with this? The problem is that it isn’t a realistic strategy for reaching net zero in the fastest time possible."

Erskine also notes that deep retrofits "are not achievable for hard-to-treat homes at reasonable levels of cost and disruption," adding that "for Britain’s housing stock, this is not achievable on a timescale commensurate with the climate emergency. This point seems to be lost on advocates for deep retrofit."

He also suggests reducing the carbon footprint of heating is the most important task, and notes: "We don’t have much time to get this right, and as Voltaire once noted, the best should not be the enemy of the good. We need a pragmatic way forward."

The 80% Rule Rules

Heat loss from house in cold climate
Heat loss from a house in cold climate.

Harold Orr

Coincidentally, I have been accused of letting the perfect be the enemy of the good in my discussions of Passivhaus versus net-zero and responded to Voltaire by quoting engineer and economist Vilfredo Pareto, who said, "In any series of elements to be controlled, a selected small fraction, in terms of numbers of elements, always accounts for a large fraction in terms of effect."

This has also become known as the 80/20 rule: "80% of consequences come from 20% of the causes." In my post, Harold Orr and the 80% Rule, I quoted the designer of the Saskatchewan Conservation House from an interview in The Sustainable Home:

"If you take a look at a pie chart in terms of where the heat goes in a house, you’ll find that roughly 10% of your heat loss goes through the outside walls.” About 30 to 40 % of your total heat loss is due to air leakage, another 10% for the ceiling, 10% for the windows and doors, and about 30% for the basement. “You have to tackle the big hunks,” says Orr, “and the big hunks are air leakage and uninsulated basement.”

I concluded that perhaps I had been letting the perfect be the enemy of the good, that perhaps we needed a compromise—less Voltaire and more Pareto—and that this was the pragmatic way forward. So a yes to heat pumps, but still, a bit of fabric first, with a lite retrofit.

"Doing an Energiesprong or complete rebuild of every house in North America would take forever and cost the Earth; cutting energy use by 50% or even 80% is achievable by following Harold Orr's prescription. Once you are there, it is not a stretch to switch to an air source heat pump and electrify everything, and you are no longer emitting carbon."

'Let's Get Decarbonisation Done'

Writing in Passivehouse Plus Magazine, engineer Toby Cambray picks up the conversation in "Let's Get Decarbonisation Done"—the title being a play on Boris Johnson's "Let's Get Brexit Done." It is perhaps not the best title, given the way that's turning out, but it gets better.

Cambray works in the Passivhaus world and, after reading Erskine's article, notes: "There is a lot to unpick in this piece, and plenty I disagree with, but it did get me thinking about whether it is time to adjust our tactics in the great game of decarbonisation."

He breaks my spellchecker by verbing heat pumps, writing that while you could just install heat pumps, "this does not however mean that it’s a good idea to put a heat pump in a building with poor fabric efficiency. Although there are cases where other constraints mean we have little choice, ultimately we need to both (mostly) InsulateBritain and (mostly) Heatpumpify Britain." Heatpumpify and heatpumpification have been added to my dictionary.

Like me, he worries about the grid's ability to deal with massive heatpumpification, and that modest fabric fixes are doable right now.

"We’re not saying the grid could never cope with wholesale heatpumpification; we’re saying it would be expensive to make it able to cope. What’s more is that inter-seasonal electricity storage technology isn’t ready yet, a clear counterargument to concerns about the rollout of deep energy retrofit. With the latter, the technology (i.e., fluffy stuff) is well established and the barriers are 'just' political and logistical."

Cambray reminds us that a decade ago, the advice was very different. Air source heat pumps couldn't do the job at low temperatures and everyone was pushing "geothermal" ground source heat pumps that cost a minimum of $20,000; ASHPs can now do the job and are far less expensive. Cambray and I both made the argument that spending the money on insulation and airtightness was a smarter investment. (At least we no longer have to argue about the term geothermal when we are talking ASHP, I used to get into so much trouble.)

Cambray says he stands by his advice of 11 years ago but notes: "I think the calculus has changed. The climate crisis is more urgent, the UK heat pump market has matured significantly." He suggests that just as a fabric retrofit doesn't preclude upgrading to a heat pump later,

"Installing a heat pump does not preclude a subsequent deep energy fabric retrofit, especially if it’s planned in advance. A rapid growth in heat pumps would quickly stimulate the investment in the infrastructure needed if we're to shift away from gas in the medium term, and with appropriate forethought, we can go back and reduce the demand of those properties later."

I wondered about this, given that if you go back later, the heat pump will be oversized, which can cause problems; they evidently then "cycle quickly, causing harm to the motor. Heat pumps that are too big for your home lose efficiency and are more expensive to operate." I asked Toby Cambray about this, and he responded, "Potentially yes, hence the importance of forward planning! As in, design the heat pump with a retrofit in mind..."

Now I am just a non-practicing architect and Cambray is a practicing engineer, but as with the electrify everything crowd in the U.S., this makes no sense to me. The investment in infrastructure isn't cheap or fast, and the U.K. would probably have to put every tree in the state of Georgia into the chipper to keep the Drax generators going.

Cambray says, "I'd welcome a debate here," so here are my two pence: I continue to say the first thing to do is Reduce Demand! with a lite retrofit, Orr-style, and then Electrify Everything! insulation before heatpumpification. Fluff before forests.