Please advise someone who just got central air conditioning.

Factual Questions
1

The quick version of the question - I’m ‘balancing’ the newly installed forced air central AC. I am trying to get the third floor bedroom comfortably cool overnight without turning the lower two floors into a deep freeze. At present, I have the vents closed on the first and second floors, open on the third floor. The thermostat is on the first floor; there is a ‘return’ on each above-ground floor.

This setup did not produce the desired results. Last night, it was too hot to sleep comfortably on the third floor, while the ground floor with the thermostat was too cold. It was cooler outside the house than on the third floor, and pre-AC, I would simply have opened the windows and run a fan. I had the forced air fan switched to ‘on’ rather than ‘auto’ for a while, but I’d prefer not to have that constant noise and energy use. (Frankly, I’d prefer not to have the energy use of an AC unit at all, but I’m not the only one who gets a vote…)

I stopped running the AC in the evening at 25 C - the overnight was set to allow the temperature to rise as high as 28 C. By the end of the night, the thermostat was set for 24 C. We have a programmable thermostat that will allow for 4 different time/temperature settings for both weekdays and weekends.

Is there something counter-intuitive about AC that I should know about? Please advise me, you who are wise in the ways of AC.

2

Our condo has dual A/C units and separate upstairs/downstairs thermostats. Works quite well, but I presume not the quick fix you were looking for.

3

Yeah, different “zones” would probably be best. It’s also necessary for maximum comfort to make sure the attic/roof is properly ventilated so the rising hot air can actually leave the building.

4

We leave the fan set to “on” to continue to redistribute air throughout the house when the A/C is off, though you say you don’t want to do that. It sounds to me like your installer used a cookie-cutter approach instead of one designed for your house.

Another solution which works a little better than just closing the room vents is to install baffles in the main ducts coming out of the system. You can install levers to close off an entire branch, though feasibility depends on whether they have a different branch going to each floor. This is not short-term as in today, but probably not that hard for a contractor to do.

5

Before my brother’s baby was born, I helped him put an overhead fan in each of the 3rd floor rooms (one of them being the nursery). It’s been almost a year, and I just asked him how it’s helped and he says it helps a lot to have the air circulating up there. I suspect they have the fans set to “suck up” instead of “blow down.”

6

Is your first floor a basement by chance? If so, that’s definitely the wrong spot for your thermostat. If you’ve closed all the vents on the first two floors, I’m a little surprised that you’re not getting a decent amount of cool air up there on the third floor. In a 3 story home, the thermostat should always be in the middle floor, right guys?

7

One thermostat for 3 floors simply isn’t going to work. You need to send the cool air to where you need it, and the only way to know where you need it is to have multiple thermostats. I think there exist wireless thermostat+baffle systems that you can put into the duct work that will open and close based on additional thermostat readings.

Fans seem like a good bet too.

Also, have you checked that the air coming out on the top floor is actually cold? If the ducts are not well insulated, all the nice cold air can get warm before it reaches the exits.

8

I think it can work if it’s on the middle floor and you close all the first floor vents, and close the 3rd floor vents and reopen the first floor ones for winter heat. That’s the situation I have.

9

No, nothing counter intuitive - the fact is that the system you had installed is not ideal for a multi-level house. With one thermostat, you have a single zone system. The AC will try to satisfy the area where the thermostat is located. With three levels, a zone for each level would be ideal. One fix would be to relocate the thermostat, but then you’ll have a similar problem - the bedroom will be ok but the first floor will be freezing.

Did the contractor discuss this with you before installing the system?

10

Oh, my goodness - such a flood of replies while I made lunch…

I should clarify a couple of things - The insulation, exhaust fans, duct work and HVAC calculations were all done as part of the renovations of this house, and I have no reason to suspect there is anything wrong with the installation of the AC unit, nor the design of the HVAC system of which it is a part. I’m asking advice about its operation because I’ve never lived anywhere that has AC, and I’m not sure how to rig it so that it does what I want it to do. I think my first mistake last night was in not letting the system cool the house enough before we went to bed, coupled with setting the overnight temperature too high.

I should mention, too, that the HVAC system’s heating performance has been exactly as we’d hoped for. Of the two, the heat is much more important - people have lived in this part of Ontario for centuries without AC, but never without some source of heat for the winter.

And when the exterior temperature is in the low twenties, I’d much rather cool the house by opening the windows and shutting the HVAC off.

Vinyl Turnip Well, yes, I was rather hoping for a response like 'No, you’d think closing off the 2nd & 3rd floor ducts would do the trick, but actually because of (something I’d never thought of) you need to open them and all will be well.

troub Yes, covered on both counts. We totally removed the interior walls of this house and insulated to R24, and the third floor roof is vented properly. Pre-AC, the interior of our house was consistently cooler than the outside until late afternoons of sunny, 30+C days, particularly on the ground floor. The third floor is a challenge because it’s higher than the neighbouring houses, therefore receiving a good 16+ hours of sunlight on cloudless days.

CookingWithGas I’ll experiment with the fan switched to ‘on’ - last night was our first night with the new rig, and I couldn’t hear whether the AC was kicking in or not. It could be that I need to suck it up and deal with the fan.

** ZipperJJ** We’ve had ceiling fans in previous houses without AC, and that may be a longer term solution…

** FoieGrasIsEvil** No, the first floor is the first floor above the foundation. I have not mentioned the basement in all this, and the thermostat is not in the basement.

** sachertorte** Yes, the air coming out of the vents on the third floor is cold air.

Dag Otto Yes, as mentioned above, the unit complies with the HVAC design that we had to get back in 2007. I’m just not at all experienced in its operation, not having ever been a fan of AC.

11

I have no advice but can I come over and enjoy your central air?

12

Like Dag Otto said, you need a zoned system. Depending on how the ducts are run you may be able to retrofit dampers and add thermostats to accomplish this.

If you’re lucky.

13

But of course! I’m more accustomed to offering our guests wine, whisky or song, but I’m sure we can scrounge up some central air…

We can be easily found - there is a sign on our door that says “Dopers Welcome” in the ancient tongue. Speak friend and enter.

Just don’t disturb the waters in the front…

14

There’s no real trick to using central a.c. With a single zone system like you have, only one of your three floors is going to be at exactly the right temperature. The other floors are going to be either too hot or too cold.

If it were me, I’d set it so the floor I slept on stayed comfortable for the night and forget the other two floors until the morning when I had to go downstairs.

15

I’ve wondered about this. Which setting is which? Our fans have a switch to change the direction of the fans – clockwise or counterclockwise. Will one direction suck up and another blow down?

16

Yes. Which is which depends on which way your blades are angled …

Do you feel the direct blow in one direction and not in the other?

17

I’ve always been told that closing vents makes the whole thing less efficient. Not sure if that’s true, or true for every installation.

You definitely have to give it time to cool the place down, though. My thermostat is programmed to start cooling at 5, assuming I’ll be home around 6. The summers we have, though, it often doesn’t make it.

18

Actually, there was something wrong – the installers failed to explain to you how to operate it. You should call them up and ask them these questions. They installed it; they will want you to be satisfied with their work.

Personally, I agree that during a big renovation like this, they should have done a multi-zone system. Even if it costs a bit more to install, it will be much more efficient over the years. Even more so for heating than AC (and in Canada, you will have a lot more days of heating).

19

You have to look at the tilt of the blades. If you want it to blow down, you make it spin in the direction of the higher side of the blade. If you want it to suck up, spin in the direction of the lower side of the blade.

The best way to tell is to flip the switch and stand under it, perhaps with a tissue, and see exactly what ends up happening! :slight_smile:

20

Maybe see if somebody that has knowledge of Zone Dampers could modify your current system?