Recently a friend asked me over to see if switching from his gas furnace to heat pumps would make sense—he’d gotten advice from one heat pump installer that his house wasn’t a good candidate, and also got a separate quote of over $60k for an elaborate heat pump system. Why can’t you just switch from a gas furnace to a heat pump?
The thermal envelope, it turns out, really matters. The house in question is a poorly insulated, leaky house—in other words, sorry to say, a typical older house. Houses like that will have rapid changes in temperature inside with rapid changes and heavy winds outside, and require a lot of energy to heat and cool. Most gas furnaces are made to blow a lot of air and heat, so they can respond to sudden demands; but heat pumps are designed to hum along at a fairly even temperature, and don’t have the capacity to ramp up quickly. In other words, residential heat pumps do really well, and are most efficient, in buildings with decent-or-better thermal envelopes.
The other simple problem is capacity: this house had an existing 8-ton heating system (about 100k BTUh) connected to big ducts. There is no 8-ton heat pump you could just plug in to switch from gas to efficient electricity—the biggest I know of is about 4 tons. So you would need to redesign the ducting system to break up the house into two smaller zones, and as you can imagine, complexity, expense, and disruption of the house would increase. The $60k+ quote he got was for—get this—3 outdoor heat pumps with EIGHT indoor units—linesets everywhere, lots of equipment to maintain, and, yeah, expensive. All to heat a poorly insulated house.
What to do– choose a bigger hose, or a bucket that doesn’t leak? This is a good case for insulating first: with insulation and air sealing, the heating load can be reduced drastically, often by 50% or more. This will require some expense and disruption on the house, but once you do it, you need less expensive (smaller) HVAC equipment, and you’ll spend less on heating and cooling forever– you will have locked in that efficiency for the life of the building.
The Expense Equation
Let’s not kid ourselves—the insulation job won’t be cheap either. To do it right means dealing with the roof—probably by spray foaming the underside of the roof deck to reduce stack effect and heat flow, get a few inches of the correct type of insulation on the existing foundation walls, and in this case, with a brick structure, consider putting exterior insulation over the brick with new siding over it. All of that will run in the neighborhood of $60k I should think, and then the HVAC system might now be down around 30k. Good news is there are many incentives out there to offset those costs—with new on top of existing federal incentives for efficiency upgrades, and a $10k retrofit incentive through our local village, the bill may come to more like $50k: less than the wasteful options, with way lower energy bills and a more comfortable house. Maybe I was guessing too low and the total may come out to around 70k after incentives—even so, there would be a tradeoff of lower energy bills for increased loan cost, maybe close to a wash.
Future Energy Costs?
None of the above even takes into account where energy prices are going. Almost as certain as death and taxes are rising energy costs. Between extreme weather, supply chain, and war in Ukraine, it’s been volatile lately, and my hunch is it’s not going to just quietly settle down quickly. To reduce energy use at home, especially with renewables and backup batteries, brings some peace of mind as well as lower bills. I would say it’s worth it.
Following a presentation for Greenbuild today (a free event you can see the recording of), some in the audience asked for the Resource list I had on my last slide. I’m including it on this blog post. TBDA is not affiliated with any of these companies and don’t have any commercial interest in them, but they are all products or resources that we have used in our projects and think are worth considering.
Building Science Corporation: tons of papers, insights, tools, like this article on spray foam, and this one on conditioned and unconditioned attics. Free!
Also from Building Science Corp’s Joe Lstiburek is the Builder’s Guide to Cold Climates, an excellent detail reference for architects and builders.
Building Science Fight Club: great lessons for architects, great Instagram feed.
Passive House Institute US (PHIUS): certification, training, and continuing ed. PhiusCon 2022 will have new thinking on the Revive program.
DOE Healthy Indoor Environment Protocols for Home Energy Upgrades
Rocky Mountain Institute: thinking on efficiency and health, like this article on gas cooking risks
UL’s Greenguard website for healthy materials and products
• 475 Supply (membranes, tapes, ventilation, insulation, skylights, instruction)
• Global Wholesale Supply (Steico wood fiberboard insulation etc)
• Small Planet Supply (membranes, tapes, insulation etc)
• Prosoco fluid-applied air sealing products
• Henry Blueskin peel-and-stick air barrier membrane (exterior air barrier at my house)
• Alpen High Performance Products, US-made triple-glazed, insulated frame windows and doors.
• Also check with your local salvage places like Habitat ReStore for salvaged materials. We’ve used salvaged flooring, old-growth lumber, and some fixtures to good effect.
Payette’s window comfort calculator and also PHIUS’ window comfort and condensation calculator: beyond energy performance, it’s good to know whether windows will be comfortable to be near, and whether they will create condensation in expected temperature ranges.
Now that we’re done with most of the decarbonization work on my house—gas line cut off, heating and cooling with minisplits, using heat pumps for water heating and the condensing dryer, cooking with induction—I have some observations and items for follow-up:
Of course you need to insulate correctly, but air sealing is vital
- When you start with a good insulation and air sealing plan (as you should!), you really do get increased comfort, especially when the house is poorly insulated (i.e. all old uninsulated houses). Ours just feels so much better now—virtually no cold spots or drafts, the double hung windows being the exception. I’ll replace them when they’re close to dead, probably 5-10 years.
- A good insulation and air sealing plan for older houses is likely not too simple. Yes, it’s fairly simple to retrofit walls with cellulose (drill and blow), easy to pour cellulose in an attic; but neither of those are simple to air seal, which is arguably just as important as the insulation. And old slabs and foundations are likewise not so simple to insulate—water management (in the form of bulk water and condensation) can be challenging, and water-resistant insulation materials more expensive.
- We haven’t seen the usual Fall/Winter mice since buttoning up the thermal envelope…airtight is rodent-tight!
- We need to keep looking for straightforward ways to answer the question, “how much and what type of insulation and air sealing is right for this house?”
Energy Grid and Infrastructure Needs
- What level of efficiency should we meet for buildings, if we want to have a zero carbon grid? If we just switched from gas to heat pumps now, I think we’d need more power plants. Not good—there is so much waste we can eliminate, but how much do we absolutely need to?
- Many (most?) houses will require electrical service and panel upgrades. If decarbonization becomes required by code, for instance, there should be a grant or other incentive program, certainly for lower income households.
Physical, Financial, and Mental Benefits
- Since the goal is to get the house airtight, ventilation becomes necessary—and boy is it nice! We have the CERV, and it’s been so great to have a better-smelling house, and one that we can ventilate with the push of a button. The recirculation function of the CERV redistributes air in the house, and whether in vent or recirc mode, it filters the air, so the air is cleaner inside.
- Cooking all-electric with induction means more beeps. Beep stove on, beep burner on, beeps if you lift the pan off the burner, and the electric tea kettle beeps…I suppose in the near future it will have whatever voice Siri or Alexa or Grond, Warhammer of Morgoth, whatever floats your boat.
- The electricity bill is a lot more variable now—the cold spell in January meant a $200 electricity bill (first winter all-electric, and I only have just under half my solar PV installed). Still less than my neighbor’s $380 gas bill, which they got on top of their electric bill!
- Gas bill is $0 ad infinitum. A consummation devoutly to be wished (just reread Hamlet, wordy and wonderful low-carbon Dane).
- Some of the benefits of decarbonization are qualitative: the psychological sense of security in a more resilient building, comfort, and the beauty that is incorporated in design and finishesl. Physical and mental health are mutually dependent.
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We are making progress on my home decarbonization project—the old slab was removed, basement wall and under-slab insulation was added (big oops on the underslab XPS order—this stuff is HFC-blown, but there was an ordering and availability snafu);
and the new slab poured (with new columns installed for the main beam for longevity);
siding was removed;
basement windows were replaced and peel-and-stick air barrier was added;
the walls were filled with cellulose (through holes drilled from the exterior);
then continuous wood fiberboard insulation was added;
the electrical service was upgraded from 100A to 200A (there was some debate as to whether this was necessary, with the possibility of load sharing technology);
the gas line was removed; a new heat pump and duct system was installed for heating and cooling; a new conditioning ERV was added for ventilation;
new appliances were installed, including a heat pump water heater, induction cooktop, and heat pump condensing dryer;
the basement was drywalled;
we’re currently finishing rebuilding the soffits and facias;
and next we move to rebuilding the back room walls.
The house feels different in a good way—it definitely fluctuates in temperature less with all the added insulation, the HVAC system is so gentle and effective, and cooking with induction instead of gas is a pleasure. I’m so looking forward to getting the back room rebuilt so we can run a blower door and check our airtightness.
Our studio atmosphere and project and CAD standards provide great support for onboarding and ongoing employees, and offer a great learning opportunity for emerging professionals. Please contact us for more information on our open Project Manager/Designer position.
One of the advantages of working closely with my friend and builder, Eric Barton (Biltmore Homes), on my own home renovation is the chance to literally get my hands on all the materials we’re using, and to discuss material techniques and strategies as we go. It’s not the textbook approach where the builder reads the plans and specs and installs exactly what the architect said; it’s the architect and builder looking at the crawlspace ceiling, scratching our heads, and asking, “how can we do this without spray foam?” That sort of thing.
During the August 25th Green Built Home Tour, I described the moment I had when we removed the gas line from our house as part of this project. I no longer had a pipe coming into the house with a gas that could catch on fire, kill me with carbon monoxide, and poison my family every time I cooked. Having it gone was surprisingly visceral. I’m getting the same with the materials.
What really struck me over the weekend while I was painting trim and installing foundation insulation was the emotional connection to material. When you cut wood trim, you get sawdust. Don’t breathe it in, but it has a nice wood smell; cut cement fiber board trim, and you should be afraid—you should fear the silicates that you really shouldn’t breathe in. Cutting wood fiberboard insulation, you make compost; it’s totally different from cutting EPS (Styrofoam), with horrible white plastic pellets littering the jobsite, impossible to contain. The list goes on and on, but the upshot is that we can and should build durable, beautiful buildings from non-toxic materials. Some are harder to get than others, but aside from current supply chain issues, they’re getting more available as the design and construction industry demand them. So keep demanding!
Another recent experience we had on a project was an attic spray foam job that continued to smell days after installation. If the spray doesn’t cure properly due to the mix or the temperature, the uncured or still curing material can smell bad and contain some toxicity. Also, according to an experienced foam installer I know, apparently supply chain issues in the chemical manufacturing of the foam components has resulted in some bad batches.
It seems that from the late 19th century to now, we have created and deployed so many toxic materials—lead, asbestos, PFAS, vinyl, benzene and other various petroleum by-products, coal ash with its heavy metals, microplastics… while right in front of us we have wood, cellulose, stone, adhesives without added formaldehyde, solar and wind power, and so on. Check out our resource document for products, documents, websites, and more.
A guiding quote by Frank Lloyd Wright: “Study Nature, love Nature, stay close to Nature. It will never fail you.” We don’t always have all the information we need on every material we get our hands on, but I will always be looking for those feel-good materials as close to Nature as possible.
I decided to take the leap and decarbonize my 1919 frame bungalow. This was born out of several things: first, we were at the end of service life on the gas water heater, within 5 years of service life on the furnace/AC (inefficient gas, poorly installed), and the soffits and fascias had begun to fall off the house—the squirrels were having a heyday. My walls still didn’t have retrofit insulation, and my enclosed back porch was poorly enclosed in the ‘40’s, with some band-aid level solutions I had installed to make it tolerable. Plus, the house featured an original basement, which is to say, a cracked slab that didn’t keep moisture, radon, or critters out, and no insulation down there. In other words, about 60% of my interior was nasty and uncomfortable, and the rest needed help, too. The driving motivation was a combination of a sense of stewardship and adventure—doing the right thing by my building (which would make for a more durable and much healthier and comfortable living environment), and experiencing first-hand technologies like the heat pump water heater, mini-split heat pumps, induction cooking, and good ventilation with energy recovery. Yes, it’s expensive, but I’m fortunate to be able to finance this given historically low interest rates. This project will teach me a lot, allow me to teach others, and beyond the enjoyment of it for many years, I think it will pay off in the long run. I began with the question, “could I make my house a Passive House?” The answer was yes, but it meant having to replace my roof (which was insulated in 2010, when I had no grand plans and little money), and having to pull out my existing windows (replaced in 2004, when I hadn’t heard of Passive House or triple glazing, and “airtight” was a term nautical designers, not architects used). So, while it was possible, I didn’t think it made sense to spend a lot of money throwing away serviceable items. My next question was, well, if I can’t make all the PH metrics, can I make the PH Source Energy limit? In other words, could I cut down my total overall energy usage to Passive House levels, even if space conditioning energy is a bit high? In doing so I would employ all the PH strategies at my disposal: minimizing thermal bridges, insulating, making the house airtight, using an ERV for ventilation, and using efficient lighting and appliances, plus some solar PV. The answer was yes, it’s totally doable! In fact, I could approach annual Net Zero by adding some more solar.
Check out these visualizations of our energy modeling:
Here are the strategies I employed to get there:
Exterior walls: these are leaky and poorly insulated, and were also covered with asbestos siding. I hired a remediation crew to remove the asbestos; next we will strip off the old siding and expose the original sheathing. We will drill holes in the sheathing so we can pump cellulose into the walls, and then we’ll cover the sheathing with a diffusion-open (meaning it lets moisture “breathe” to the outside) peel-and-stick air barrier membrane, sealed at all penetrations, sealed to the foundation, and sealed as best we can to the roof. We’ll then cover that with a diffusion-open wood fiberboard insulation layer, creating a thermal break at all studs. The fiberboard is essentially a negative-carbon product, having absorbed carbon while it grows, and being repurposed from waste product. Over the fiberboard go furring strips and new siding. This is more than a face lift—it’s like major reconstructive surgery!
Basement: an 850s.f. conundrum. Over the years, whenever I would come up with ideas to expand the house up or out, I always came back to “yeah, but I would have to deal with that basement.” Dirty, cold, wet, and leaking radon (just enough to be concerned), it’s a lesson in why capillary breaks and waterproof insulation are needed. The more I thought about it, the more I realized that insulating the basement plus good HVAC would mean I would have 850sf that I could actually enjoy for art studio, guests, music, laundry, etc. It would mean tearing out the old slab and putting in new windows, but it would really change the way I look at about 40% of the house. Also, replacing the three old wood structural columns with new ones (on stand-off bases) means I don’t have to worry about those degrading by wicking up moisture from the ground. For the windows, I decided to go with Marvin fiberglass double pane; while triple pane is my choice for comfort and energy, especially on larger windows, these are small units in less-used rooms, and I thought it made sense to save over a thousand bucks here.
HVAC and water heating: with a much-improved thermal envelope, I have the opportunity to have a much smaller, energy efficient heating and cooling system; and by replacing the old gas water heater with a heat pump electric type, I will have eliminated most the gas use (cooking and dryer only remaining)—almost there to all-electric! For space conditioning, this meant mini-split heat pumps, of course, like we use on most our Passive House and low-energy projects, since they’re very energy efficient. I wanted the system to function properly, so planned to replace the ductwork so it would be properly sized and well-installed (airtight). I chose a conditioning ERV (the CERV2 from Build Equinox) so that I would have demand-controlled ventilation, good airflow, great filtration, and a modest amount of conditioning when I’m ventilating. The water heater is Rheem Proterra 50-gallon heat pump unit I picked up at Home Depot. It will cool the air in the house in heat pump mode; I don’t see this being a winter comfort problem since it’s in the basement, and the conditioning system will offset the losses—but it will be good to live with it and get first-hand experience.
Appliances and PV: the last remaining items were the range (switching from gas to induction) and dryer (switching from gas to a heat pump condensing dryer). I decided to commit to these with the rest of the project so I could eliminate my gas line. I already have 12 solar panels on the house (kind of jumped the gun, but got them the last year that the Federal tax credit was 30%, before it got reduced) and plan to add some more to offset my increased electricity use (even though everything will be very efficient, I’m using electricity for heating, water heating, cooking, and dryer now, so overall electricity use will go up as gas goes to zero).
Other problem areas: common to a lot of older renovated houses, my front and back porches were enclosed long ago, and were not properly insulated. To fix that, I’m reframing the back porch walls and installing triple-glazed (Alpen) windows; on both, I’m insulating the floors with a few inches of closed cell spray foam for airtightness and condensation control, topped by loose fill insulation (less carbon intensive)—we’re still working out the details of this in light of material availability.
You can follow the progress on Instagram where we upload images from the project. Also, Tom presented this project on the Green Built Home Tour session on “How to Prioritize Sustainability Upgrades for an All-Electric Home” and you can watch that video here.
Following up on the last post introducing the idea of decarbonizing existing buildings, this post features a flow chart that illustrates decision points and issues for decarbonizing homes in a cold climate. There is plenty of complexity in any building project, arguably more so in renovations; so this isn’t a how-to guide so much as a view into our thought process about the different facets of a project like this. We expect this to change as technology advances and we complete more projects of this type.
Please feel free to download our Decarbonization Resources with links to our recommended websites, products, and organizations:
In the US most of our buildings are not optimized for indoor air quality, energy efficiency, or today’s living patterns. As our building stock ages, and as appliances and HVAC systems, windows, and finish surfaces reach the end of their service lives, we face an opportunity to radically upgrade: we can refashion our buildings toward a positive vision of the future.
Since the 1970s, researchers and the DOE have studied building science* to determine climate-specific recommendations for levels of airtightness and insulation, ventilation and conditioning systems, and efficient appliances. Following these best practices leads to more durable, comfortable, energy efficient environments with far greater air quality than is typical. These to me are the goals of all building, whether new or retrofit, and they can all be done while upgrading appearance and function. Even without going to extremes, houses in most of the US, including our Chicago climate, can achieve 75-100% energy use reduction while weaning off fossil fuels. All the technology and know-how we need is available right now.
To give a sense of the scale of the issue, consider the Chicago region: since we’re a cold climate, nearly half of residential energy use goes to heating. According to 2010 Chicago data, residences collectively use about 24 trillion kWh annually; if these used a sustainable 3,500kWh per person annually, that would be reduced to about 6 trillion—a factor of 4 reduction, while leaving fossil fuels behind. Most of the energy that goes to an older home, typically a leaky and poorly insulated building, is wasted; but with good retrofits, we can get there. I will demonstrate how in my 1919 house I achieved an 84% energy reduction in five steps, which also meant a 75% reduction in my required furnace (which becomes heat pump) capacity.
So what are the roadblocks? The first, as I see it, is lack of vision: it’s easy to remain entrenched in our old, fossil-fuel age, poorly ventilated mindset, and therefore extend our low level of performance. It takes some analysis and experimentation to get beyond that. In TBDA’s remodel and retrofit work we often chart a path to low- or zero-energy use for clients, with the understanding it doesn’t all have to be done at once; but the near-term steps shouldn’t hinder the long-term goal. You have to see down that path ahead, and knowing how each step is contributing to your big goal keeps the motivation high!
Another problematic-at-scale roadblock is the use of real estate for short-term profit. A flipper or developer doesn’t have incentive to do more than code minimum since they won’t get the financial or health benefits of a higher performing building. A production builder may lock in an inefficient thermal envelope and mechanical system for 25 to 50 years—and we only have 10 to get in front of catastrophic climate change. This will probably require demand, and either financial incentives, stricter regulations, or both.
Next, the question of cost: the knee-jerk reaction is that it costs substantially more to build at a higher level, but studies have countered that. True, a couple exhaust-only bath fans are cheaper than an energy recovery ventilation (ERV) system; lots of insulation costs more than little insulation in the short term. But when you look at life cycle costs and the health effects of the envelope, you may have a different value scale than the flipper or production builder. For new construction, the cost to build to a very high level of performance is, from our research and others we’ve seen, only in the 1-7% increase in initial building costs—easily justifiable by long-term energy savings and increased comfort and air quality. This small a margin is within the range of trade-offs for tile or countertop costs, or slightly reduced (better designed!) square footage. In retrofits the math can be harder, but sometimes forgiving, since you face the need to replace aging infrastructure like mechanical systems or windows.
Thus far, each retrofit we’ve seen is unique, but themes and prototypes are emerging. In our next posts, we will be showing case studies to discuss the design and goal-setting processes, building science, energy modeling, and cost issues. In particular we will attempt to outline cost challenges where they occur so that policymakers can understand where incentives will be needed to get us on track. This is our decade to make a difference.
*Retrofit energy modeling begins at 3:07 of video above
** Resources include Deep Energy Retrofit Guidance from the Building America Solutions Center, NREL’s Standard Work Specification website for home energy upgrades, Building Science Corporation’s trove of research papers, insights, and Joe Lstiburek’s wit, the Green Building Advisor website, PHIUS, Fine Homebuilding, Journal of Light Construction, and other publications.