Boilers and AC in the age of sustainability and efficiency
October 15, 2023 2:05 PM   Subscribe

I am buying a house, yay! The boiler is from 1969 and is leaking methane gas, yikes! Are there better options than an old fashioned gas boiler? I'm also looking at putting in high velocity AC (i.e. SpacePak/Unico) and wonder if it's worth it to add another unit to zone the first and second floors.

I've had a very thorough inspection of the house (1923 Chicago bungalow) and while it has plenty of things that need attention given its age, it is very sturdy and very well taken care of (there's original linoleum and tile in almost perfect shape and 1" of cement behind the kitchen walls). The one thing the inspector was insistent about was that the boiler has to be replaced as soon as I take possession.

In (almost) 2024 surely I should not simply replace the boiler with another gas boiler? I'm keeping the radiators although somehow I have never had radiator heating in all of my years of renting. This is a big purchase and I want to do my due diligence and get some information before I simply trust the repair person. Is there something that can run more efficiently, use less fuel/cost less to run, and be less polluting?

The other project I'm taking on right away is replacing the carpet in the entire upstairs with flooring (cork, hardwood, TBD). I figure it might make sense to put in AC at that point, when AC tubes can be more easily installed to service both floors. While my realtor recommends mini splits, but I just hate the way they look. Whenever I've stayed somewhere with them I've been so put off and know I don't want to live with them. Adding soffits/traditional ductwork to this vintage house is a non-starter.

Do you have any tips for either of these big projects? Zoning/managing HVAC without wasting too much energy? I am committed to keeping as much of the vintage character as possible. The roof will need to be replaced in 5-7 years so at that point I could look into solar if it makes sense based on the mechanicals I put in. The inspector recommended adding some additional insulation as a stop gap until the roof is done. It's a lot of decisions to make all at once, I'm doing this without a partner to back me up, so any ideas or experience would be helpful.
posted by Bunglegirl to Home & Garden (23 answers total) 3 users marked this as a favorite
 
We have a Unico system. It's not zoned and I wish it were, but this is a pain point with any type of AC system, not only high-velocity. We are otherwise very happy with our system, although it can be noisy. Weigh the expense vs. the irritation of one story never being the temperature you want. Only you can make this judgment call.

We also have an ancient gas boiler and have thought quite a bit about what to do. To have radiator heat, you do need a boiler of some sort; they make electric boilers, but they aren't common in the US because gas has traditionally been so much cheaper for heating. There's also something known as a hydronic heat pump but they barely seem to be available in the US. The other thing to do would be rip out the radiators, install ductwork, and put in a heat pump, but who wants to do that?

A local heating/cooling company would likely be happy to come in and consult with you about this. We had one do an "energy consult" which was helpful and we talked about many of these issues.

Not an expert but that's my experience owning a house of similar age and features!
posted by baby beluga at 2:25 PM on October 15, 2023


Do you know more about your radiators, like are they steam or hot water? If steam, are they single-pipe or double-pipe? Depending on what type of radiators you have if you want to keep them you might not have options like "zones," and in some cases you might basically only have the option of replacing your existing boiler with the same boiler but newer. But it might also be possible to replace your existing boiler with a newer type of boiler. (I have a 1925 house with a boiler of a similar vintage to yours and single-pipe steam radiators, for which there are very few boiler options.)

As for mini-splits is it the inside or the outside appearance of the mini-split that you dislike? There are different form factors for the inside part - my next door neighbors have one that looks like a piece of art (like, a piece of art that sticks weirdly far off the wall, but still) when it's not in use. I think it's an LG Art Cool.
posted by mskyle at 2:30 PM on October 15, 2023 [1 favorite]


If you're already thinking of putting in an AC and you want to not use gas, the obvious answer is to install a heat pump, which provides both heating and cooling. You'll likely want a split system, with a number of heads to condition different areas, all connected to one outside unit. You probably want to get someone knowledgeable in to look at options for your house. You can get units that fit in the ceiling, in the wall, in the floor or otherwise are less obtrusive than the classic mini-split look.

Make sure you get a heat pump with good cold weather performance, such as the cold weather models made by Fujitsu or Mitsubishi that still heat at -15F and below.

In theory, you could install an air-to-water heat pump that provides hot water for your radiators and separately install an air conditioner, but that would be kind of silly.

I would highly recommend getting an energy audit so someone can come into your house and see where you are losing the most energy and give you recommendations. It might be that the best bang for your buck is air sealing, it might be insulation in the walls, it might be insulation in the basement headers, it might be the roof, it might be replacing windows, etc. Getting a professional to look at this with you will help you sort out what is worth doing and what isn't, so you can make a plan, even if you aren't going to do all the work at once. For an old house, making the house more efficient is usually a better place to start than solar panels.
posted by ssg at 2:34 PM on October 15, 2023 [5 favorites]


We have a high-velocity system and it is noisy as fuck. Totally disruptive every time it clicks on, which of course is many times a day. It interrupts conversations, makes it hard to hear TV dialogue and is just a constant drag, the only thing I hate about my home.

I would recommend that you maybe find someone with such a system already installed and experience it for yourself before you commit. Installers will tell you that they can mitigate the noise, and I'm sure that's true to some extent, but I doubt you'd have much recourse after installation if the sound performance wasn't as good as you expected.

Our system isn't from either of the manufacturers you mention, though. It's possible their equipment is better than what we've got.
posted by AAAA at 2:38 PM on October 15, 2023 [1 favorite]


The split heat pump system is still worth investigating. Minisplit wall mounted head units are somewhat intrusive, but there are also ducted minisplits that suit.

They're usually a smaller unit, and 'ducted split' here means 'from a convenient hidey hole to the neighbouring room(s), and cooling just one area', not 'from the basement to the second floor and venting everywhere', so their space needs are less than you would need for a whole house system. It might be possible to stash one in a closet ceiling or the attic, for instance, but an installer who knows their way specifically around ducted minisplits would no doubt be able to advise.
posted by How much is that froggie in the window at 3:08 PM on October 15, 2023 [2 favorites]


If you put in a heat pump, you may be eligible for discounts and tax credits through the Inflation Reduction Act, as well as other possible savings on other things you are doing to your house. Check out Rewiring America. In addition to fighting climate change, you could save a bunch of money.
posted by hydropsyche at 3:14 PM on October 15, 2023 [5 favorites]


The relative costs of operation (gas vs minisplit/heat pump) depend on your local cost for gas and electricity, unless you're producing the latter yourself. In many areas of the country, it is either of roughly equivalent cost to heat by gas heat and minisplit, or minisplits are cheaper to run. But that depends on a lot of factors, including local utility rates, weather (minisplits are most efficient at moderate temperatures), house layout, etc. As a data point, we put minisplits into a 200-year-old house in Philadelphia, and it was cheaper to run them in the winter than the gas steam boiler we were replacing, and they were vastly more efficient (and much quieter) than window AC units in summer.

To me, if you want AC, minisplits are a no-brainer. As comments above said, you don't need to put ducts in and you don't need to do the ugly traditional-minisplit-head-on-the-wall look. There are different styles that would work. If you have a single-story house with attic space above (I think you need something like 16" or 18"?), you can put in ceiling-mounted heads (e.g., here). You'd put that in the ceiling, centered roughly in the middle of the room, and they usually have conditioned air coming out all four sides. You can also do mini-ducted minisplits. This doesn't involve visible ducts like furnaces. Instead, you mount what I believe is called an "air handler" either in the ceiling or at the top of a closet (here, here). You can then mini-duct 3 or 4 very short runs from that to bring conditioned air to adjacent rooms. For instance, if you put that handler at the top of a closet, and there were two bedrooms and a bathroom flanking the closet, you could duct to all three of those with the one handler. All that inhabitants of the house would actually see are a few small vents in the wall or ceiling (they vary, but, for instance, this, this). Sizes and styles vary by brand and BTU size. You can read more here.

My recommendation here would be concealed minisplits (either of the two types above, or something similar). If you go with minisplits, you should first get an energy engineer to do a manual J calculation to determine heating and cooling load. It will cost probably $500 and it's well worth it. Minisplits have some amount of sizing flexibility built in, but you don't want to massively oversize, and many contractors do oversize. This means that they don't dehumidify well and cycle on and off, making them less energy efficient. We hired an energy engineer to do a manual J calculation, and it turned out that almost all the companies doing estimates wanted to over size by around 50%. We insisted on going with the smaller size and have been very happy. You also want to think about room size and layout when you're doing a minisplit plan - how many heads you need total, how many BTUs per head, which directions they're pointing, etc. It sounds complicated, but the result is cheap and efficient heating and cooling, with the possibility of making it carbon-neutral later with solar. Also, YMMV, but someone we know put in high-velocity mini-ducts, and it was very expensive and extremely loud when running.
posted by ClaireBear at 3:54 PM on October 15, 2023 [6 favorites]


If you have hot water radiators, particularly of the standing cast-iron type, you can replace the existing boiler with a "mod-con" boiler (Modulating and condensing) for a significant increase in energy efficiency and reduction in pollution without hacking up your home too much. If you have one-pipe steam radiators a high efficiency boiler won't be an option, and if you have fin-tube baseboard rads, a condensing boiler might not make as much sense unless the baseboard rads are grossly oversized. (basically, if your rads are oversized for the btu/hr loss of your home, a condensing boiler can work at peak efficiency because the home can be heated with low temperature water. Almost all standing cast iron installations have grossly oversized rads, that's less common with fin-tube baseboard, which often runs at up to 180deg water temps)
Electricity is really expensive in IL, so I'd think hard before committing to a heat pump.
posted by Larry David Syndrome at 4:00 PM on October 15, 2023 [2 favorites]


Also, as someone above mentioned: if you do go with minisplits/heat pumps, you definitely are going to want cold-weather-specific ones, living in Chicago. We splurged for Mitsubishi Hyper-Heat (100% heating capacity at 5F, and guaranteed heating capacity down to -13 F): when we did this project several years ago, Mitsubishi Hyper-heats were one of the only options for that. My understanding is that various companies now make similar. I believe they're only $500 or so more expensive, per machine, than the normal ones. Otherwise, your minisplits will lose efficiency/juice as the temp dips below freezing, just when you need them the most. So definitely go for the low-temp-specific one, regardless of what brand you choose!

I agree that a modulating and condensing boiler might be a great option, but they're expensive, and then you still have the problem of air conditioning. If you don't want/need AC, I think that sticking with gas may make sense. If you want AC, I still think your best option is a minisplit solution. Even with expensive electricity, I still think minisplits may well be the same cost to run as a gas boiler, and they certainly will be a lot cheaper to run than window units in summer. Might be worth seeing if your realtor can put you in contact with someone locally he/she knows who has them, to ask them about operating cost. Or perhaps you know someone already.
posted by ClaireBear at 4:08 PM on October 15, 2023


Some more potentially helpful info here.
posted by ClaireBear at 4:14 PM on October 15, 2023 [1 favorite]


We bought a 1912 ~3000 sqft 3 story Milwaukee house that came with a single-zone Unico system that worked remarkably well, and preserved the character of the house without being obtrusive or excessively noisy.

However, it came with a heating oil boiler, along with heating oil deliveries, which were neither economical or environmentally sound. We replaced the heating oil boiler with a Veissman modulating/condensing gas boiler (per Larry David Syndrome's post above) and experienced both a remarkable decrease in energy costs and energy use, while experiencing a surprising overall comfort level while re-using the existing radiators and without changing any of the character of the home whatsoever.

While both heat and AC were single-zone systems in a 3-story home, it was easy to live with 71 or 72 on the first level, 75 on the second, and 77 on the top. There were baseboard heaters in "problem areas" that the previous owners had installed, and we never used them after installing the new gas boiler.

We considered a heat pump, but since the Unico system was already installed and worked well, and since we did not want to impact the character of the house with the installation of many mini-splits, the mod/con gas boiler made the most sense. In addition, electricity costs in Wisconsin were quite high. It's a decision I don't regret in the slightest and it worked well and with surprisingly low gas usage, a perfect match between efficiency and reuse of the existing radiators.
posted by eschatfische at 4:18 PM on October 15, 2023


I have a 1935 Cape in New Jersey. We have single-pipe steam radiators and a natural gas boiler. We put in a Spacepak system with a heat pump over 10 years ago.

With spacepak (and I assume other high velocity), there are sacrifices with efficiency that mean the heat pump isn't as efficient as it could be with a more standard system. It only works until a bit below freezing out for the heat (due to what was available 10 years ago) and so we only use the steam radiators in the coldest part of the winter.

The high velocity, at least as installed here, is not noisier than other ceiling-mounted AC vents.

Due to the layout of the house, I still had to sacrifice a corner of a bedroom to get outlets into all the rooms on the first floor. I also lost a chunk of a closet. Given that, if I could do it again I would consider conventional ductwork, or at least get more opinions on what would be possible.

I do wish we had put in zones but not only would it have been more expensive, there's something about the number of outlets that would have meant we needed a ridiculous number per room upstairs.

We're thinking about a minisplit now for part of the basement the system doesn't get to; the neighbors have one and I love how quiet the outdoor unit is compared to the large central units.
posted by miscbuff at 4:26 PM on October 15, 2023


Response by poster: When I hear mini split I think of this, which I now realize is not necessarily the case. Still, I would want to see as small and few vents as possible. I'm not sure about what exact kind of radiators I have. Most are the old fashioned looking ones from the 1920s, there's one baseboard heater in the kitchen which has a separate gas line, and one electric heater in one of the two attic bedrooms. Here's some examples from the house, not great pictures but all I have at the moment.
posted by Bunglegirl at 4:36 PM on October 15, 2023


Response by poster: There is lots of room behind the knee walls (with easy access panels) upstairs to install AC system parts, whichever I go with. I figured duct work could run through the floor but it doesn't look like that is done typically? There is no room on the main floor for extra equipment (no entry closet even), but there is an unfinished basement.
posted by Bunglegirl at 4:44 PM on October 15, 2023


Those look to be hot water radiators (the air bleeders at the top are a giveaway, steam radiators don't have them.)
These would be ideal for use with a mod-con boiler. Hot water heat is really nice- no noise, no drafts , it's not a dust distribution system. Also, if you have cats they will LOVE them.
posted by Larry David Syndrome at 4:51 PM on October 15, 2023


I have a 1920s bungalow also in Chicago and although our house was already converted to a regular forced air gas furnace and A/C when we bought it, I do have one thing to warn you about: It gets HOT on that second floor in the summer. Our A/C does not reach up there with enough cooling power to cool it down, and because it's a converted attic there is not sufficient insulation so the sun just beats down on the roof and heats up the entire space. I wish we had mini-splits or a zoned system. Our neighbors just full-on installed a second A/C condenser unit on the roof of their sunroom to cool the upstairs, and pretty much everyone in the neighborhood has either that or window units in their second floor windows -- even if they ostensibly have central air.

We make do with the U-shaped Midea window units but even that is difficult, because the tiny windows don't open enough to install them easily (we literally have to remove various parts of the windows and pull out one sash entirely to get the unit in and then put it back.)

I really hope to move to a heat pump/mini split system when our system fails, though I haven't personally lived with that kind of system so I can't tell you the pros and cons. I just can't imagine what else would work in these homes.
posted by misskaz at 5:13 PM on October 15, 2023


I have a 1920s house downstate from you. I installed a modern condensing boiler and it's been great!

Relatively inexpensive to install and extremely efficient. It's also very small (like the size of a backpack), and quiet. This is what Larry David mentions above. I bet your house is a good candidate and highly recommend getting a quote on that kind of install before you make your final decision.

Other benefits of radiant heat include that it doesn't dry out the air, and it's nice to sit on or next to a radiator in a way that it isn't with the other options mentioned.
posted by SaltySalticid at 5:30 PM on October 15, 2023 [1 favorite]


We have steam radiators and had to replace a gas boiler; here's just a recommendation for a resource: I enjoyed learning about steam heat from Dan Holohan who writes about old radiant (which includes steam and hot-water) systems. He started a forum website with lots of info about both: HeatingHelp.com. For example, here are some tips for replacing a steam or hot-water boiler. I'v found the site to be worth nosing around, both for the articles and for the forums, where professional contractors answer odd little questions from each other and sometimes homeowners (including "I found this weird looking thing, what is it" type questions that come up in older homes)
posted by LobsterMitten at 6:22 PM on October 15, 2023


With a modulating/condensing boiler (we have a Triangle Tube), you should look into pairing it with an indirect water heater for your domestic hot water needs. They're hard to beat for efficiency (at least in the winter time).
posted by sportbucket at 6:32 PM on October 15, 2023


To follow up on my comment above, with a heat pump, you can distribute heat or cold in more than one way. You can take the hot/cold refrigerant, transfer that heat into air and then blow the air around the house (this is the conventional North American model and is a logical way to go if you already have air ducts throughout your house). The other option is to distribute the hot/cold refrigerant around the house and then transfer that heat into the air much nearer to the point of use. That's what I'm suggesting you might want to look at is it is easier to retrofit (you're only running small pipes), quieter, and it allows more control of temperature in different areas.

My opinion is that, from a sustainability standpoint, we have to think about the long-term impacts of our choices. Any heating system you install today should be operating for decades. To me, committing to fossil fuel based heating for a few decades into the future makes no sense at all. We clearly need to stop burning fossil fuels as soon as possible and so it makes no sense to spend a significant amount of money to lock a long-term commitment to fossil fuel heating. In that context, using electricity is the logical choice and a heat pump is the way to make that feasible.
posted by ssg at 6:52 PM on October 15, 2023 [1 favorite]


Oh, I had also wanted to say that there are potential tax incentives for energy-efficient upgrades. This includes HVAC systems, along with things like hot water heaters, windows, insulation, appliances, etc. Would probably be worth checking what your state and national tax incentives are for the various options under consideration, and how that affects the all-in price for each.

Also, and you may well know this, but it can make a big difference, both in terms of energy efficiency and in terms of comfort, to upgrade things like insulation and windows. Our 1920s house has horrendously leaky windows: sitting within about 7 feet of any window means you can feel very pronounced drafts coming in. If you're concerned with preserving the historical character of your bungalow, you can buy windows that are a better historical fit (i.e., not vinyl), but those come at an increased cost, of course. Since it looks like your attic is finished, you'd need to see what the insulation options are. I believe there may be a possibility of adding flat high-density insulation when you replace your roof (basically, 2" foam sheets under the new roof), but you should consult an expert. I say this because ideally any short- to medium-term energy upgrades would be taken into account when sizing the next heating/cooling equipment.
posted by ClaireBear at 6:58 PM on October 15, 2023


Still, I would want to see as small and few vents as possible.

It's certainly possible that you're just different from me, but let me urge you to prioritize quiet.

Yeah, those ceiling head units are bigger and uglier than the little vents from a high-velocity system. But once they're up and (presumably) painted to match the ceiling/wall, you're not going to notice them. They're going to turn into some of those features that your eyes just stop registering unless they change somehow.

But an HVAC system loud enough to make you reach for the remote control? That shit pisses you off afresh Every. Fucking. Day.
posted by GCU Sweet and Full of Grace at 8:07 PM on October 15, 2023


Oh man, just came in to be jealous of your hot water radiators! I have an air heat pump with furnace/central AC in a teeny little 1940s house (under 1k sqft) and I've looked into adding radiant heating even though I don't need it with this furnace simply because it's so much more enjoyable than forced air.

Kudos on the house - you'll be shocked at what you've learned to do in a few years :)
posted by esoteric things at 8:54 PM on October 15, 2023


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