Replacing window AC units with another cooling system in an older home

I presume this belongs in IMHO rather than GQ or MPSIMS; moderators, feel free to move it if I’m wrong.

We’re looking at houses, and we found one we liked. Great location and a decent house with a lot of potential (in our inexperienced opinions). It’s old – built in the 1930s. It has one feature that I really don’t like – it’s cooled by window AC units. Heat is old-fashioned radiator heating (I’m pretty sure it’s a gas boiler with hot water radiators in each room), which I don’t have experience with but from what I read sounds acceptable. But in my experience, window AC units are a huge pain, inefficient, and they’re ugly as hell. Living in the DC area, we’ll be using AC for nearly half the year.

If we buy this house, what are our options to upgrade the cooling system? There is no ductwork, which means that in my understanding forced air cooling would be very expensive to install. I’ve read a bit about ductless cooling, which sounds intriguing, but I don’t have any experience with it. In my understanding from googling, ductless cooling is actually ductless heating/cooling – would that be compatible with the radiator heating? Would I have to get rid of the radiator heat? Are there other options to consider? Thanks to anyone with experience/expertise on home heating/cooling who can provide input!

Window ac units also make it easier for bugs to get in.

My parents had a duct system installed in their old house. I believe the total cost was under 10k for everything, however they have a bunch of metal colored tubes running around the basement to create the ducts.

If you have an unfinished basement that isn’t bad. But without a basement, or a finished basement it would be very ugly looking.

I have a home with steam radiators, overall the heating experience is fine.

If I was looking for cooling, I’d probably go with a Split system, where you have the condenser outside, and piping of refrigerant to an indoor unit that blows out cold air. They’re fairly straightforward to install in an old home, not as unobtrusive as forced air cooling, but a big step up from window units.

I’ve also heard about high velocity systems that use much smaller ducts that would be easier to install in older homes.

Sounds perfect for a Mini Split Heat Pump.
Cold AND hot.

If the heating you currently have is old, it’s probably really inefficient. If so, get rid of it and go with a heat pump.

Also, if you’re reasonably handy with tools, they can be installed by the homeowner.

I agree with splits. Cheapest option and efficient. You can mount the indoor units near the ceiling and use remotes to control them. When we lived in Africa, all the embassy housing had them.

Another vote for the mini-split. It’s not as convenient as central air but it’s a helluva lot easier as a retrofit.

I have nothing useful to add, but I’d like to nominate this sentence for “most confusing when taken out of context”.

Thanks for the suggestions! We’ll definitely see a professional if we decide to pursue this house more seriously.

I put a high velocity, narrow-duct system into an old home with hot water radiators. I love the hot water radiators – they are reliable, don’t blow crap through the house, and there aren’t a lot of drafts or cold spots.

The system wasn’t cheap. There’s a big piece outside, and another big piece in the attic. We have one big tube in the attic, and a lot of narrow tubes, which vent into the ceilings of various rooms. It’s a little noisier than large-vent AC. It works well, and is comparably efficient to traditional AC. The guy who installed it did a really good job of putting the ducts where they are minimally in the way of walking around the attic and using it for storage.

We also looked into the Japanese-style ductless system. That would have cost about the same, and would have required us to mount the units in every room. They have the virtue that each unit is independently remote-controlled, so you only cool the rooms you are in. But then there are a lot of parts to keep track of, feed batteries to, etc. The real issue for us was that we didn’t have a lot of wall space we were willing to stud with units. (And we had no problem putting a lot of little holes in the ceilings.)

I recommend you got a couple of quote for both, if you have the energy to do so. And look at the plans that go with the quotes. We got two quotes for the small ducts, and one was MUCH better than the other. Not so much in cost, as in the guy who wrote it up had a much better sense of the geometry of the house, and was going to do a better job of running fewer tubes in more useful places. He also put all the vents in the ceiling, and none in the floor. I hate floor vents. I’m always paranoid I will drop something into them, even when I’m just visiting someone.

I have a ductless mini split and like it a lot. If the downstairs is a fairly open plan it will cool several rooms with one wall unit. Ours does the living and dining room, kitchen and down the hallways. You can get them with multiple air handlers but they don’t seem to make real small ones. If a bedroom just needs an 6,000 BTU window unit it might be best to use that. I think the smallest units were 12,000 BTU when I bought my system. They don’t require you to do anything with the heating system you already have.


If you have a basement and attic, adding AC is fairly straightforward (assuming a 2 level house). If your house is 1 level then either one should be sufficient to get what you want without too much hassle.

Our house has neither a basement nor an attic. We put in AC anyway. It was a pain and required quite a bit of thought on how to get things accomplished – but in the end, totally worth it.
And money. It cost money. Our friends who have an attic and basement put in AC more reasonably priced.

Personally, we didn’t like the look of a split system (also sometimes called ductless). It would have been much cheaper to install split systems, but we went with the more complicated route (we were remodeling part of the house anyway).

If one has zoned A/C, where each room has it’s own system, when one dies the others will continue to work.

Our DC rowhouse has a mini-split unit in the basement and central air in the rest of the house. The AC unit is in the attic and the ducts run through closets and between walls. It was pretty affordable and I have the name of the DC area contractor we used if you would like it (PM me).

Really depends on the house. In one like ours, 4 floor ~120 yr old row house, no ducting of any kind originally, even a small diameter/high velocity duct system is a pretty big deal to install if you’re not remodeling otherwise. Even a mini-split would have been somewhat more complicated to install on all four floors because on the fourth floor there would have had to have been evaporator units (cool air coming out of them) in rooms away from the back wall so coolant and condensate pipes running through rooms, or cut into the drop ceilings. So we just did it on three floors: bottom floor has two evaporators in separate rooms with pipes coming up from the basement, 2nd and 3rd floors are basically one big room each so one evaporator each on the inside of the back wall, central (compressor) unit on the outside of the back wall. 4th floor was kids’ rooms, empty now except occasional visitors who use window/floor (the ones where a hose goes out the window) units. Happy with the system, more cool but electricity bills are lower than they were even with just the two of us. We shut the ones besides the master bedroom one off at night, and that one off in the day time. It’s close enough to true central, for us, NY area climate. We don’t have heat pump feature because that doesn’t really work in this climate. ~$22k, but it’s not really cheap to do anything to this house.

Thanks for all the input. We made an offer on the house, but there was another offer and ours was rejected. We’ll stand by to see if any of the contingencies fall through (and since it’s a very old house, that’s possible), but for now we’re moving on and looking at other places. I’ll keep all the input in mind if we find ourselves in a similar situation!

When we lived in NJ we had central AC put in, and it was simple and far cheaper than I had anticipated. The heating system there was compatible.

But here in California we got someone to look, and he said that our heating ducts and registers were too small. And they were in the floor. He didn’t even give us an estimate.
Our windows are not very good for a window unit. I looked at a portable unit, and it would have worked, but luckily last summer was cool. Here in the Bay Area there is usually only a few days where you need it anyhow. Assuming climate change doesn’t get us.
So in a 1930 hour (mine is from 1952) it depends.

100% ductless mini split. You install these on the bigger air spaces (living room, master bedroom, etc) and let convection (and wall vents if you need them) handle the rest.

The compelling reason - the reason why ducts are stupid - is the SEER rating. The minimum systems these days give 15 SEER, and 18 SEER units are available for a bunch more.

Mini splits routinely come in at 24 SEER (so 25% less power than an 18 SEER) and there are some that are 38 SEER (50% of the power of an 18 SEER). And they cool and heat, and in most climate zones except the far north, the higher end units are able to heat year round. And are more efficient and lower cost than natural gas except when it is very cold outside.

And you get zoning out of the box, you only have to fully heat or cool the rooms you are in. There are smart thermostats you can get that interface to mini splits, and you can connect Alexa to them. I have one, I can say “Alexa, set the <room> thermostat to <a number> or ask her to lower it/raise it/turn it on or off/set fan speed”.

Daikin is widely considered to be the highest quality brand. But Cree units have a higher SEER rating, they are a pure Chinese brand, probably of lower quality. Pioneer makes some cheaper ones. You can DIY install them, it’s not very hard, but you do need to be a reasonably competent handyman to pull it off and to not take any shortcuts on the electrical connections and cabling.

You do not need to get rid of your radiators, you can leave your old system installed. It would just be a backup source of heat for you in case one of the splits fails or on a really cold day in DC and the heat pump isn’t heating enough. If the old system ever fails on it’s own, though, you could just scrap it and use a couple electric blankets as backup.

Get a estimate, and it depends on your home style. Some homes, such as high ranches can easily cool the upstairs with a conventional A/C due to the attic access. Other homes or the downstairs of such a home may do better with split systems.

But don’t assume that central a/c is cheaper to run. I went from about $135/month electric bill central a/c to about $85/month by installing a large window unit which cools 1/2 the house (all the living space) + bedroom window a/c’s. Electric bill without a/c is about $50/month. As you can see electricity is relatively cheap here, but I believe the numbers can scale up.

And split A/Cs would have been half that, they are double the efficiency of window units or more. (even “energy star” window units have a SEER rating around 12-14)

So $17.50 over my base power bill instead of $35 for wall units. About $50 or so per year. What matters is not the efficiency, but the bill. $50/year for 10 years is $500 dollars saved, 100 years is $5000 saved, split systems that last for 100 years still can’t pay back what window units cost (assuming window units too can last for 100 years). Perhaps if they lasted 2000 years we would get to parity.

But can you provide a link to the double efficiency, I’ve heard how efficient they are over window units but when I hear the power bills they seem to be paying much more for that high efficiency they like to claim.