Home Improvement → AC: wall unit vs window units

Blue: windows
Green: Suggested placement for the wall unit by three different salesmen from three different places

I live in a condo on the second floor, just under the roof. We're only in May, and today temps rose up to 31C inside. I'm a polar bear. I have a window unit in my bedroom and a fan hitting me directly. I sleep comfortably at 18C/64F. 20C/68F top. The rest of the place is just one big sauna.

I can't even fathom what it would be like to live here in full Summer when we get 40C/104F temps outside. So I've been shopping around, looking at wall units. I was quoted about 2500$ with install for a 18,000 Mitsubishi model (no inverter, no heating. Elsewhere, prices vary from 2000-3000$ for reputable brands. I could get a cheap House Brand for 1800$, maybe...

The thing is, I am renting. The landlord lives under me. We're friends now. He'll buy back the unit at about 50% of what I paid whenever I move out, and he will adjust rent accordingly.

The condo is 1013 square feet. According to my research, I'd need a 18,000 BTU unit at least. The West, South and Eastern walls face outside. The northern wall is adjacent to the next unit.

However, I was wondering whether or not I could get away with two additional window units (8,000 BTU each). That'd be 24,000 BTU total, though I imagine it's not as simple as that.

Say I need to drop 1000$ for two extra window units. Compared to a 18,000 wall unit that I'd end up paying about 1250-1500 out of my own pocket, although the initial capital investment is three times that.

Am I looking at similar efficiency here? (3x 8,000 BTU window units -vs- 1x 18,000 BTU wall unit) cooling wise? The only thing that would bother me is the electricity bill with three window units. I recon it could easily triple my bill if they run 24/7 for a few weeks during the hot summer days.

I don't trust the word of salesmen. They obviously want to sell me their wall unit.

Anyone experienced has an approximate idea? I don't need exact numbers or anything.

I have one thing to say: 3 window units will be noisy as HELL.

I can live with the noise. I've been sleeping with one on for the past few years.

A single large unit is more efficient than several small ones, but only if you can get the cooled air from it through the whole house efficiently, and I don't see that happening with your floorplan, even if you set boxfans in the doorways.

I would go with several smaller units, or get a central system, a single large wall unit isn't going to reach the whole house. It would make one room nice and cold, but everything else would be warm.

When you say "wall unit" are you referring to a sleeve unit that you see in hotel rooms or are you talking about a ductless mini-split? And, how will you be using the new system(s)? Are you looking to spot cool specific areas of the condo or are you trying to keep all the areas in the condo at a uniform temperature? Also, is there an attic above you or is it a flat roof? What about insulation?

Insulation is almost non existent, sadly. Building was built in 1983, condo was renovated inside this year, but it all went into new floors, walls, cabinets, etc. Basically the entire inside is new, but nothing was invested in insulation.

It was 31 outside today, and 31 inside. There is an attic under the roof.

I am especially looking to cool the two most important rooms where I spend 99% of my time: the office (bureau) and my bedroom (chambre 1).

By wall unit I meant a ductless split unit, yes. In French it's called a "unité murale" so I just translated it verbatim. My apologies.

I already have a 8000 BTU window unit in my bedroom. It's loud as f*** but it keeps it down to 68F at night which is how I like it.

The salesman said a 18,000BTU would be able to cool the living room (salon) and office well, but the rest of the condo wouldn't be as cold.
I showed him these exact plans, but I wasn't convinced myself. I don't see any way in which a ductless split unit could cool down chambre 1 sufficiently by being placed where it was suggested.

Is there such a thing as a quiet AC unit?

Mini-splits can be VERY quiet, and can have multiple inside evap/fan units using a single outside condensor. They can be very nice. It's virtually guaranteed to be quieter than a window unit.

I would never, ever, ever, ever invest any money in a rental. Get window units that you can take with you. The LL should be paying for permanently installed units UP FRONT, not you.

If you are comfortable with giving him free property improvements, make sure you get the arrangements in writing before you do anything.

This was the plan, to get it in writing before I had ANYTHING installed. LL even proposed it.

I was just looking at what would be most cost-efficient in the long run.
But even if a ductless split-unit would cost say 40$ to run per month (electricity in Quebec is the cheapest in the entire American continent) vs say, 100$ for three window units, the cooling would probably still be more efficient with three window units. And the setup investment is considerably cheaper.

I don't see how installing the head of the mini-split in the salon is going to do you any good in chambre 1 or, for that matter, in any other part of the condo with the exception of maybe the bureau. And, that's especially true if the rooms are closed off from each other. In other words, it doesn't appear from looking at your sketch that you have an open concept arrangement where all the rooms are open to each other in any way. In my opinion, your best option would be to keep the window unit in chambre 1, install another window unit in the salon and another window unit in one of the other rooms. Now, there is the option of installing a ductless mini-split that comes with three heads, but you're looking at a more complicated installation as well as a fairly substantial investment.

This is what the OP should get.

As far as efficiency, the multi head mini-split is the most efficient for your setup, but, Who, or What, is kept in the cage may need a window AC.. are there bars or a door on that cage? if it's just bars, it may get cool enough.

cage stands for cage d'escalier... "staircase".

multiple inside evap/fan units using a single outside condensor is obviously best option, but we're talking 5000$ according to what I was given. Not an option.

I guess I'll go with two more window units.

Thanks for the help!

i would move to someplace that actually has properly installed insulation and AC.

your proposal is to run 6 AC units at a set temperature of 64F in a structure with absolutely no insulation? that is absurd.

get the LL to insulate the attic and blow fiberglass into the walls.

There is a point at which the savings from using an efficient split unit will exceed the savings from using cheap window units. The efficiency of split units is 50-70% higher. It all depends on your electricity rates, insulation and expected usage (do you only need A/C in the evening and on weekends?).
Those factors can greatly shift the balance either way.

On a side note I lived in a ~700-ish sqft apartment on the last floor, a 10000BTU and a 5000BTU units had to start running around 2PM for the house to be bearable at 5:30PM and comfortable around 7PM.

No. 3 AC units, only one of which must be set at 68F at night (bedroom, which is chambre 1 in plan).

The rest can be set at a more resonable 74F. The weather in Montreal is extremely humid, and I can't stand humidity. AC has the quality of drying up the air. Dry 74F is much, much more comfortable than a humid 74F for me.

I definitely agree that insulation is an issue, but I'm not sure what the LL would have to gain out of it. A ductless split unit was a form of investment for him since he would easily regain it with a rent hike when I'd be gone.

But insulating? He lives under me, he has nothing to gain from it and I doubt he'll want to spend another 10k insulating this whole unit after dropping 15k on renovating it.

I'll be out of here in five years tops, three if I'm lucky and business goes well. Makes no sense to invest 5k in an AC system that will perform on par with window units I'll be able to just bring with me then.

I had considered a ductless split because I was led to believe the energy savings would be massive and it would cool better than three separate window units. The diminished noise was also a good plus, but not at the expense of cooling. Not for me.

Those Mitsu ductless splits are pretty good and I'd have no issues with recommending them. You can buy windowshakers for a lot less, but in addition to the noise, you will be running up your bill. For 3 years I'd flip a coin, for 5 I'd just get the system installed, especially since the LL is willing to split the improvement cost with you, which he's not obligated to do. Unless the heating you're getting from him is crap, I wouldn't go with heat pumps.

Insulation is more in the 800-1500 range and has immediate payback in lower utility costs.

That sounds about right on a multi-unit mini split system. We looked into it last year. It was about $5,500 per multi-unit system and we needed 2 so about $11,000. We ended up getting a 12,000 BTU portable unit for the living/dining/kitchen area then 3 wall units to cover the rest.

I live in Georgia in the hot, humid southeast US and for over 10 years lived in a 1250 sq ft house with three window A/C units - 18,500, 8,500, 8,500. The 18,500 was actually built into the kitchen wall. What made it very workable for us is that we had forced-air central heat. We rarely ran all the units at the same time, concentrating the cooling in the areas where we were at the time. As those areas cooled down, we would flip on the central circulating fan and cool down the other areas. I don't know if the OP has the central circulating fan option, but if so I would recommend this set up. As a renter. all the A/C equipment remains his. Electricity costs will be higher with multi-units, but in a geographic area where electric costs are low, this should not be a deal breaker. Just another option if it is feasible. Good luck.