Heat pump with limited home insulation — worth it?
Hi there,
We’re debating some major home improvements and are trying to understand whether installing a heat pump makes sense. I’d appreciate any and all advice you can provide!
Our situation
– 1930s home in the Bay Area, California (climate zone 3C), with very limited insulation in the ceiling and walls. Approximately 1300 sq ft. The roof is mostly flat, with two smaller peaked sections but with no attic space to speak of (i.e., there’s probably about six inches between the interior ceilings and the exterior roof).
– Windows are dual pane, older but in okay condition.
– Home is a little drafty. For example, we need to seal the fireplace.
– We currently have a large floor furnace in the front of the house (no ducts).
After freezing this winter we’ve realized we need to upgrade our heat but want to do it smartly in terms of increased comfort, costs, climate change goals, etc.
Here’s where things get complicated. I understand that in an ideal world, we’d insulate the walls and ceilings first. However, we have some knob and tube electrical wiring, and can’t foresee opening the ceilings and walls to replace the wiring given the costs (and because they won’t help with our heat needs).
We’ve received some mixed feedback from HVAC companies about the feasibility of installing a ducted heat pump. One company said our home was too energy inefficient for a heat pump to work effectively. Another said a heat pump was feasible.
Another wrinkle: we need a new roof soon. One options we’re exploring is whether a foam roof on the flat portion of the roof would provide enough of an insulation “bump” to make a heat pump more feasible. We also want to keep the door open for doing solar down the road (which may mean a foam roof isn’t feasible since it could be harder to add solar to it later).
Lastly, even if a heat pump was feasible, we’re worried about what skyrocketing electricity costs would mean for our monthly expenses (on top of a much more expensive heat pump).
Thanks in advance for your insights!
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Replies
Pay someone to do an energy audit including a blower door test and create an energy model for the house. Then have them create a Deep Energy Retrofit plan to get you to your goals, accounting for required maintenance and any upgrades and interior renovations.
Good goals are net zero on site energy, electrification without an electrical service upgrade and minimal embodied carbon, starting with building envelope improvements to get the comfort, quiet, draft free and improved indoor air quality.
The Passive House standard a great place to start. check out https://passivehousecal.org/ they have a directory of people that can help as well as a project map to look how others have done it.
Thank you so much!
JE, I 100% support Frank's suggestion and order of tackling your project. You need to know what needs to be addressed and in what order...a properly done energy audit will provide you with the information you need. Good luck.
Frank has a great answer.
Random comments:
- If money is tight, you can lease solar, take a loan, or otherwise get it with minimal out of pocket. Foam room is fine for solar if you just do it at the same time. You mention fearing electricity cost. This will address that.
- Does foam work? Sounds like you have no "real" insulation? I have an Eichler in the Bay Area and when I got my foam roof, my house went from 100% heater on all the time to taking a day to could down because the slab was so hot from being on all the time (in floor heating). It's hard to overstate the difference doing from "no" insulation to 4 inches of foam.
- Insulating the walls will certainly help with the heat. Also consider that if you have no insulation in the wall, you likely have a really poor seismic situation (no hold downs, no shear wall, etc.). Sorry to be the bearer of bad news.
- Heat pumps work fine with no insulation, you will just have to get a bigger one that if you insulated first. Of course, if you insulate after getting an oversized heat pump, you will end up with the wrong heat pump in the end (assuming you insulate later).
- My non-professional opinion is to attack in this order:
- Weather strip - if you think your house is "drafty", fix this first. If you have a fireplace with no / poorly operating damper, deal with this. Weatherstrip doors or other places it is drafty. This is low cost and will make a noticeable difference if you have a real problem here.
- Foam roof with financed solar. I would prefer to purchase the solar up front, but if money is tight, so be it.
- Look into mini splits. They are easy to install (advanced diy or pro), don't require ducting for a house that has no attic, and are cost effective. You can get very efficient ones. You will get AC at the same time you get heat. You can put them in every room or where they are needed.
- Insulate the walls. Replace the wiring at the same time.
Good luck!
Really appreciate your thorough reply!
If you have a usage history, read this article on how to size a replacement furnace or boiler based on historical fuel usage:
https://www.greenbuildingadvisor.com/article/replacing-a-furnace-or-boiler
The issue isn't so much that heat pumps don't scale, it's the equipment costs. If you need to double the size of a heat pump you're pretty much going to double the cost. Boilers are much simpler devices and often the only difference between different capacities in the same product line is the orifice or fuel jet installed. So if you need a lot of heat it doesn't cost a whole lot more.
But read the article and compute your needs, you may be surprised.
Thank you, DC! Appreciate it.
Without solar you probably will end up paying more to heat no matter what. I switched from a gas furnace (ducted) to a minisplit in ~1400Sq ft circa 1900 house in the south bay and my heating costs increased by quite a bit. It's possible I could reign in the costs by insulating the half of the house that is still original to 1900 but that is it's own can of worms with the lath and plaster and stuco ontop of siding ontop of clapboard sheathing. Thankfully I did a manual J that seems to have been accurate since the minisplit seems to run continuously mostly on low with a setpoint of 68 and my main motivations were to get rid of gas appliances and we're almost there, we just need to get rid of the gas water heater now.
Lastly, depending on your budget (we didn't have much outside of equipment costs) I would consider installing yourself. I had trouble just finding installers that would come out to put a mini split in for me and the quotes were crazy high, instead for $500 in tools you can get setup to do your own install.
You can have some "hard points" installed for a future solar installation when reroofing to make things easier. Hard points are just strategically placed pieces of framing that extend up through the insulation layer (and sometimes all the way through the roof), to give a solid location to mount the solar system rack to. I always recommend doing this when you have the option, since it makes a much more secure installation. You just have to be sure to put those hard points in useful locations, so it would be worth talking to your solar installer before reroofing, to get an idea as to how to lay things out.
A well insulated home is NOT necassary to use a heat pump. A well insulated home just requires less BTU to heat, which makes things easier on a heat pump just as it would make things easier on a gas fired furnace or any other heating unit. I sometimes see people say you "have to have a well insulated and air sealed home to use a heat pump", but that's not true -- you'll just need more BTUs worth of heat from ANY heat source if your home is leaky or poorly insulated.
I would consider insulating prior to installing the heat pumps though. Insulating and air sealing will do wonders for the comfort level of your home, and once that's been done, you can upgrade the HVAC equipment with a better idea of what you'll need.
Bill