Buying and renovating a house – are there any “deal-breakers” for electrification?
schwza
| Posted in General Questions on
I’m planning on buying a house in the next two or three years and renovating it to be all-electric, and using solar to offset some or all of my electricity use. I would improve the insulation and air sealing but hopefully not change floor plan or change/add ducts.
I know there are various reasons that a house could not support solar, but I’m wondering if there are reasons that a house could not have heat pumps. For example, I think (correct me if I’m wrong) that even if there are no ducts I could use mini splits and ductless HRV’s (e.g., Lunos). Are there any reasons that I’m not aware of that would make a house unsuitable for heat pumps?
The house will likely be a ~3500 square foot historic house in Worcester, MA (climate zone 5A). Thanks for your help.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Search and download construction details
Replies
Nate Adam's has a free course on electrification that's worth taking. Existing (well installed) ducts would make it easiest. Adequate electrical service is important, especially for a house that size. There are very few electric solutions for hot water systems and nothing for steam systems.
I've taken it, and yes, it was very helpful. One thing that prompted my post here is that he is down on mini splits because they don't ventilate well and I wanted to see if ductless HRV's would solve that problem.
Schwza,
Ductless and ducted minisplits don't ventilate well because they aren't ventilation systems. They are heating and cooling systems. If you want a ventilation system, you need to install a ventilation system. More information here: "Revisiting Ventilation."
Very helpful, thank you!
Minisplits don't do a lot for room-to-room airflow, but you could potentially put in a ducted air handler just for the blower if you really wanted to.
Aside from that, I don't see any major issues to going all electric. You will want to have sufficient electrical service, which would be 200 amp service these days. There is a "400 amp" service option too, that is really 320 amp service, but it's often overkill. It may be better to just put in two 200 amp panels, but it depends on the layout of the home. Sometimes you can save some money by putting in a subpanel at a far end of a house to serve one wing to cut down on lots of runs of small cabling, for example.
You'll want to do a good job of air sealing and insulating to help the minisplits handle the load. I would try to coordinate that work with any electrical upgrades so that you only have to open any walls once. If an electrician has to fish cabling inside an insulated wall, it's both a pain in the butt for the electrician, and it will also mess up your carefully detailed insulation in that stud bay.
Note that for this (electrification) to result in reduced overall emissions, you have to use ONLY heat pumps and similar things. If you use electric resistance (common for water heaters and electric driers), you will end up INCREASING your emissions compared to just using natural gas, assuming you have natural gas available at your home. The reason for that is that in most areas of the country, the electric grid is supplied primarily from a mix of coal and natural gas, and it's less efficient to burn natural gas to make electricity to use for heating compared to just burning the natural gas for heating directly.
Bill
I think Bill's response here is very good.
I was going to mention the following, but it would just be reitterations:
-Plan for larger electrical service to cover all your new electrical loads (ASHP, H/ERV, Induction, etc.). You may need more than 200 Amp if you are planning on vehicle charging. I'd error on the side of caution and follow Bill's recommendation for (2) 200 Amp panels or the 400 Amp service.
-What constructions are you looking at? With structural masonry, the interior retrofit will be quite elaborate. Take a look at 475's masonry retrofit assembly for reference. If interior insulation retrofit is all that is on the table, I'd tend to veer towards a wood framed house just to cut down on the complexity of the assembly.
-I think in MA a lot of the existing systems are based off of boilers and radiators. If you wanted to keep this approach, you could look into what an air-to-water heat pump would look like. I believe this approach will have trouble making hot water on extremely cold temperature days, so you'd need to plan for some supplemental heat. If you did go this direction, you would only need to plan on the ductwork for your ventilation system.
Hope this helps!
-Scott
-
Thanks!
Regarding your comment about beefy electric service for EV charging, that MIGHT be the case, but not always. A regular EV charger takes a 240v, 40A circuit, and can easily go into a typical 200A panel with normal 200A service. That's what I have right now for my Volt's charger. If you're going with one of the bigger chargers for something like a Tesla, then you MIGHT have an issue if you also have a lot of other electric loads that will be running simultaneously.
It may be cheaper to get a seperate meter for the EV charging, and many utilities have discounted EV charging rates. If you go this route, the seperate meter for the EV charger can feed a simple "disconnect", which is a small box with a single breaker in it, and that can feed the EV charger. This will be especially advantageous to anyone looking to add an EV charger that would otherwise need to upgrade their entire electric service, replacing their main panel. It will usually be cheaper to add the second meter and small disconnect. It's also possible to tap a seperate disconnect off of the main meter in most cases since the code allows for up to six "mains" in a structure. If you do this, make sure you do it correctly -- I would recommend having this work done by an electrician and not as a DIY project.
Bill
Sounds like make a wish list of your items and do some electrical load calcs to see where you’re at.
Thanks for the information and the encouragement!
> -Plan for larger electrical service to cover all your new electrical loads (ASHP, H/ERV, Induction, etc.)
I haven't done any research on panels but I'm sure once we get closer to buying a house I will. We have one car right now that I charge at work. We'll probably buy a second car at some point, but we drive rarely enough that we can probably charge on 110v.
> What constructions are you looking at? With structural masonry, the interior retrofit will be quite elaborate.
This is a very helpful point. I hadn't thought much about the difficulty of insulating a brick house, so that's a nudge towards looking for a wood house. I hadn't seen 475 before, but that is a cool site.
> I think in MA a lot of the existing systems are based off of boilers and radiators. If you wanted to keep this approach, you could look into what an air-to-water heat pump would look like.
I haven't looked into these too much, but it is true that boilers and radiators are common in Mass. I read once (long forgotten the source) that older radiators were designed to use 180 degree water and are often too small for modern 120 degree systems. Heated floors sounds pretty amazing though.
The simple approximation is that the heat output of a radiator is proportional to the difference between the surface temperature and the ambient air. The average surface temperature is estimated as the average of the input water temperature and return water temperature.
It was conventional for much of the golden age of boilers to design the system for 180F input water and 160F return water, so average temperature of 170F. With a room at 70F that's 100F difference. Let's say your heat pump produces 120F water, one thing you can do is increase the circulation rate so the temperature doesn't drop so much, let's say you have return water of 110F. Which gives average temp of 115F, difference of 45F. So you would get 45% of the heat output.
If you improve the insulation of the house so you only need 45% as much heat, you're all set!
In reality you'll want to engineer the system. A lot of times in old houses they didn't do any engineering, they just put in the biggest radiators that would fit, and they're oversized to begin with.
But an important caveat: in an old system with cast iron radiators and boilers, the water inside is going to look like the stuff that drips off of your car in a New England winter. Heat pumps tend to be more delicate than boilers and that crap might clog the heat pump. It may not be practical to reuse the radiators or the piping.
But again it might be. Every house is different, these are just things to look out for.
DC, with proper maintenance of the system -- which means TESTING the water AT LEAST annually and adjusting the corrosion inhibitor mix accordingly, you will have MUCH MUCH better water quality in the system, and longer life of all connected components.
Most residential people probably just fill the system and forget about it, aside from putting in makeup water. It's worth the extra step of testing and adding corrosion inhibitors though.
Bill
Bill, I think your second paragraph hits it on the head.
To make things worse, the default seems to be to leave the makeup water valve open. So if there is a small leak in the system it goes undetected forever, with a constant influx of fresh water which brings oxygen with it for fresh corrosion, and dilutes any corrosion inhibitors or antifreeze you might have in the system.
Leave that valve closed. If you system needs topping up, find the leak, and top up with the proper mixture.
DC, that "leave the makeup valve open" thing is an issue in commercial sites too. I had a customer once that did a multimillion dollar building renovation, including putting in a new hot water heating system in place of their old steam system. They did two dumb things:
1- They kept their old leaking water meter to save money, so their brand new project still had a bucket under the old, blue (from corrosion!), leaking water meter.
2- The control logic in their building management system had no alarm function for excessive makeup water. I think makeup water adds should always have some logic that goes something like "gee, I've been adding makeup water for a LONG time now! It must be leaking somewhere. I should beep so someone comes to check! BEEP BEEP!"
Alas, they did not do this. The system put in makeup water for months on end. At some point a contractor working on something else discovered a huuuge pool of hot water in one of the service tunnels under the building, which we jokingly referred to as the "hot springs". They probably paid for, and wasted, thousands of gallons of water as a result. This could have been prevented by some simple alarm logic in the control system.
Residential systems should be checked periodically too. The best way to prevent big and expensive future problems is to catch, and repair, small problems when the repair is still inexpensive to do. Maintenance is very important. I always stress to my customers that's it's important to consider maintenance needs when designing their buildings and systems. The easier it is to maintain a system, the more likely it will actually be maintained. A few codes to NOT follow (always do more than code!):
1- Code mandated minimum lighting levels in mechanical spaces (and basements!) are much too dark. Use more lights! Make it so with the lights on, you can see and work comfortably.
2- Code mandated clearances are usaully too small. 3 feet in front of an electric panel really isn't enough to comfortably work on things. Try to allow for 6 feet of clearance, or at least 5 feet if you're tight on space. This makes it much easier to work on things.
3- Don't forget service outlets near anything that you might need to plug something in to test!
Lable breakers and valves so you know what goes where. If you have a boiler, use the nice decals on the pipes that say what is in the pipe and show the direction of flow. Commercial supply houses have all of this stuff, and it's all cheap. Color coding the labels is a good idea too.
An advantage of my work with critical systems that can't go down is that I have to think about how to maintain everything while it's running, or at least minimize the time it takes to do any work that requires a shutdown. Clear markings, color codes, and lightning really help. Keeping required documentation nearby in a binder is helpful too. Make it easy to do the work and it's more likely the work will get done properly.
Bill
Deleted
I have lived in a historic home for the last 40 years. I suggest that you think twice about your project. Houses are systems and trying to force new systems into old houses becomes a workaround at best. To get it right you will need to rework much of the interior and exterior to get the building insulated and air sealed. You may need to reside the exterior, change windows, and repair/replace interior walls. The electric systems will all need replacing. Probably will need a new kitchen as well. The outside will be covered with line sets and solar panels, not a historic look. Comfort will be a challenge. If you want to go all electric, look for something more suitable. If you want an old house then upgrade the insulation and air seal where it makes sense and tune up that steam boiler. Maybe some solar panels if you can stand the way they look. You will still need a new kitchen.
What Jonathan said. The entire house has to be considered as a system. Our 100 yr old reno in Eastern MA started as an incremental (lol) upgrade and ended up stripped down to studs and board sheathing. We went back in with an exterior wall assembly properly implementing water, air, vapor, thermal layers. Ducted heat pumps for all floors. Full rewire with 200 amp and removal of all the knob and tube.
I hear what you're saying, and I appreciate the honesty. This will be a bit of kludge in the best case - my spouse wants a historic home and I want an all-electric home with solar panels. We're both fine with the other's preference but not super enthusiastic about it. We would very likely want a new kitchen anyway, and we're moving from an expensive city (Somerville, MA) to a cheaper one (Worcester, MA), so I'm not too worried about spending money on things like insulation and upgraded electrical. Right now we're just in the early planning stages and I'm trying to figure out if there are any characteristics of the house that would preclude electrification.
Don't let these naysayers convince you otherwise.
The most environmentally friendly and sustainable thing you can do is retrofit an existing home. Being mindful and re-using existing buildings and resources is of the upmost importance in our current environmental climate. If you can electrify and decarbonize, you are doing a great thing.
It will require more money and more planning, so just get ahead of it and plan accordingly, hire the right people, do things right.
That's my 2 cents
-Scott
I think you need to think very carefully about your goals as they are almost mutually exclusive if I understand them. All electric and keeping the original interior walls and trim.
It would not be unusual for an old house to have a huge old furnace 300k BTUs. Replacing that much heat with heat pumps would be a big ask.
Safely adding modern insulation to old walls is risky business even when you are willing to strip the walls back to the studs.
Old wall are poorly flashed by modern standards they got away with it because the old walls had lots of heat moving thru the walls to evaporate the water and lows of air moving thru the walls too carry way the water vapor. Modern insulation and air sealing without modern flashing is a recipe for disaster.
Walta
Yeah, a lot of old houses just can't be made energy efficient without altering their character. And all-electric just doesn't seem to scale the way an old fossil-burning boiler does.
Here in DC they built tens of thousands of\ houses in the 19th century where the exterior walls are brick with plaster applied directly to the brick on the interior. There is just no way to insulate those walls and preserve the character. The best you can do is insulate from the interior, which means removing all of the interior finishes -- and also losing about a foot in each direction, which is noticeable as these houses tend to be narrow.
Many of these houses are in historic districts where you cannot alter the exterior.
We did a deep energy retrofit on our last house, built ca. 1890. Eventually, the project included stripping and replacing all interior and exterior finishes and all of the utilities. The project happened over time, but we knew from the start that it would eventually be a gut&rehab of the entire place. Total cost was similar to new construction, but we saved (or reproduced) the character of the original home. It can be done, but it is not cheap in terms of time, labor or money.
Have you considered building a new energy efficient home that meets your needs but is true to the historical styles your wife loves? It can be done and done well. These guys are in Boston and do some really nice work: https://www.vintagebuilders.org/
New construction doesn't have to automatically mean "builder grade" with no character or sleek modern. You just have to find a good architect and builder who understand and appreciate the classical styles.
Utilizing existing buildings is of the upmost importance right now, if we have any shot in limiting global warming to 1.5C.
Continuing to demo old, build new, and put out additional unnecessary carbon emissions is going the wrong direction.
Why are you trying to dissuade someone from pursing an incredibly sustainable project that will work to decarbonize the built environment?
You tend to get lots of nifty interior trim details in historic houses too. I particular love the way the old hardwood floors look. Lots of them have very ornate crown moulding too.
Put in some insulation, take care with detailing so you don't have moisture problem, and replace "historic" old single pane windows and you'll have made MAJOR improvements in energy efficiency.
Bill
Who said anything about demolishing an old house to build a new one? I pointed out that it is possible to get a new efficient house with old house charm.
Rehabbing an old house to modern standards can be incredibly wasteful too. It doesn't have to be, but it often is.