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2.5 ton AC in a larger house

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  • May 15th, 2020 2:36 pm
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[OP]
Deal Guru
May 29, 2006
10197 posts
2753 upvotes

2.5 ton AC in a larger house

hey everyone, can someone advise on this situation, we had a AC quote today, and our house size needs a 4 ton AC, however out furnace and venting will only support a 2.5 ton AC, he said it will still work, but it might struggle on really hot days.

the house is roughly 2400 feet, its well insulated, in Alberta, not much humidity and we don't get super hot here.

the price is good, but im worried about buying something that is just not going to get the job done. I don't want to replace furnace and duct work, as that's working fine, the house is 9 years old.

so lets say its a 29 degree day, and 15 overnight, and I set the ac to keep the house at 21, what can I expect here, the house to stay at 21? increase to 23-24? increase to 27?
29 replies
Sr. Member
Jan 19, 2013
515 posts
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Ottawa
rocking23nf wrote: hey everyone, can someone advise on this situation, we had a AC quote today, and our house size needs a 4 ton AC, however out furnace and venting will only support a 2.5 ton AC, he said it will still work, but it might struggle on really hot days.

the house is roughly 2400 feet, its well insulated, in Alberta, not much humidity and we don't get super hot here.

the price is good, but im worried about buying something that is just not going to get the job done. I don't want to replace furnace and duct work, as that's working fine, the house is 9 years old.

so lets say its a 29 degree day, and 15 overnight, and I set the ac to keep the house at 21, what can I expect here, the house to stay at 21? increase to 23-24? increase to 27?
How do you know you need 4tons?
I doubt you need 4tons
2.5tons should be more than adequate
[OP]
Deal Guru
May 29, 2006
10197 posts
2753 upvotes
1chinaman wrote: How do you know you need 4tons?
I doubt you need 4tons
2.5tons should be more than adequate
the company said based on the rule of thumb of 600 square feet per ton.
[OP]
Deal Guru
May 29, 2006
10197 posts
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newlyborn wrote: Time to shop around who can give you right / sound advise. I would go with what @1chinaman suggested.
this guy was very knowledgeable, he said it would work, I just wanted to get some real life examples from people,
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Jan 16, 2011
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The NORTH
My last house was in Toronto and it was 3000 square feet. Had a 2.5 t AC and it never had a problem keeping the house cool in the 30'C weather even with the high humidity. House and ac were 10 years old when we bought.
Member
Feb 27, 2007
390 posts
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rocking23nf wrote: this guy was very knowledgeable, he said it would work, I just wanted to get some real life examples from people,
Hopefully you've figured out this isn't the case - a four ton unit would do your house if it was in (at least the northern part of) Florida.

Massively over-sized unless he has something to back up the sizing besides 'rule of thumb'....
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Feb 11, 2007
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Oakville
Sounds too big. My 1979 house is the same size and has a 2.5 ton unit. It used to struggle on hot days as the house wasn't insulated well, but works great after I increased the attic insulation film R18 to R60.
Since you're already well insulated you shouldn't have a problem.
Having too big an AC will cause it to under cycle, putting more wear and year on it and preventing it from removing humidity.
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Oct 14, 2010
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Barrie ON
I'm not trained as a HVAC professional, but I have learned a few things by observation. My rule of thumb is that you need 1 Ton of AC for every 1000 cubic feet. So your 2400 square foot home needs a 2.4 Tons unit, so you would purchase a 2.5 Ton.

Even if the airflow through your furnace did support a 4 Ton unit, you would find that the temperature of your house would drop in a matter of minutes and then the AC would shut off. That might sound super cool , but it presents problems. One problem is that these rapid changes in temperature are uncomfortable to humans. The second problem is that humidity in the moist summer air is condensed as it passes by the cold evaporator coils. If the unit cools and shuts off quickly, it does not give all the air within the home the chance to move across the cold evaporator coil, and now you end up with a lot of cold humid air which is only a little more comfortable than hot humid air.

I don't know why your contractor would ever suggest a 4 ton unit. Perhaps that is a way out for him, if the 2.5 ton doesn't meet your expectations. He can just say it's not my fault because you didn't install what I recommended. It could also be that he want's to sell you an upgraded furnace.

The original 2.5 ton AC unit in my 2700 square foot home would start to run around 10:00 AM and then run continuously until sundown during the hottest days of the year. My new 3 ton unit will shut on and off throughout the day, but I have noticed that the humidity doesn't drop as much as it did with the old unit.
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Oct 13, 2008
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I only have a 2 Ton York (Model AY024MA321A) from the builder ... house is 1800 sq ft ... built in 2006.

Suffice. Not broken. Still working.
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Deal Expert
Mar 23, 2009
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Toronto
Four tons sounds crazy high. Maybe if you lived in Florida.

EDIT:

BTW, it's actually better to be too small than too big. People worry about having an AC that's too small, but IMO it's much worse to have one that's too big. Read up on short cycling (or just read @Rick007's post).

I speak from experience. I live in Toronto, which has hotter and more humid summers than most of Alberta from what I understand, and part of my house which is about 2000 square feet has a 3.5 ton AC. (My house was built in two segments at different times and has two separate HVAC systems.) On the very hottest days of the summer it's good, but on not-so-hot days it short cycles a bit, meaning that it cools the room down fairly quickly but doesn't stay on long enough to account for the humidity. Thus, what I get is air that's cool but a bit clammy because the humidity is still somewhat high. It's not horrible in my setup, but it's definitely not ideal. Insulation is pretty good but room volume is higher than average since the 2nd floor has cathedral ceilings. Lots of windows too.

Once this AC dies, I'll replace it with a smaller model. Not sure what size though. Guesstimating, since I haven't done any sort of true calculation, but maybe a 2.5 ton. Any armchair HVAC specialists out there want to hazard a guess? Winking Face

On the other side of the house, it's 1800 square feet plus finished basement. Not sure of the square footage down in the basement but maybe 800 square feet, so total 2600 square feet. Insulation is mediocre, and windows are moderately leaky. I have a 3 ton AC on that side of the house, and it's perfect.
Member
Jun 23, 2019
344 posts
186 upvotes
rocking23nf wrote: hey everyone, can someone advise on this situation, we had a AC quote today, and our house size needs a 4 ton AC, however out furnace and venting will only support a 2.5 ton AC, he said it will still work, but it might struggle on really hot days.

the house is roughly 2400 feet, its well insulated, in Alberta, not much humidity and we don't get super hot here.

the price is good, but im worried about buying something that is just not going to get the job done. I don't want to replace furnace and duct work, as that's working fine, the house is 9 years old.

so lets say its a 29 degree day, and 15 overnight, and I set the ac to keep the house at 21, what can I expect here, the house to stay at 21? increase to 23-24? increase to 27?
On a 9 year old house that is 2400 square feet you should only need 2.5 ton. My house is 3200 square feet with a 3.0 ton, and it's actually slightly oversized for my house. I would suggest you get an estimate from two more companies and see what size A/C they recommend. Even if they are super expensive and you don't end up using them at least see what size they suggest for your house.
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Jul 2, 2001
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GTA
rocking23nf wrote: the house is roughly 2400 feet, its well insulated, in Alberta, not much humidity and we don't get super hot here.
4 tons for that? The guy sounds clueless.
Member
Dec 29, 2004
389 posts
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Echoing other comments, 4 ton sounds like a lot. You don't want to oversize too much.

SWO, 3250 sq ft above ground, 9ft on all levels - we went with a 3 ton.

The calculated value in the HVAC design for our house was a 2 ton. Didn't agree with that. House is Energy Star, 2012 standards.
Member
Feb 27, 2007
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da_123 wrote: Echoing other comments, 4 ton sounds like a lot. You don't want to oversize too much.

SWO, 3250 sq ft above ground, 9ft on all levels - we went with a 3 ton.

The calculated value in the HVAC design for our house was a 2 ton. Didn't agree with that. House is Energy Star, 2012 standards.
You likely would have been better off with a higher SEER 2 or 2.5 ton than the 3 ton as per the posts above. AC should always be undersized if in doubt unless you're talking about a heat pump, where bigger + a variable speed compressor would be advantageous in Canada.
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Dec 29, 2004
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von Monster wrote: You likely would have been better off with a higher SEER 2 or 2.5 ton than the 3 ton as per the posts above. AC should always be undersized if in doubt unless you're talking about a heat pump, where bigger + a variable speed compressor would be advantageous in Canada.
I agree oversizing is bad for a couple of reasons, but I disagree that 2 tons of cooling is sufficient for a 3250 + 1450 sq ft house with 9ft ceilings on all levels, and transoms everywhere. The neighbour's house across the street, identical model without the extra windows, went with the 2 ton. Builder had to yank it and upsize after the fact.

We came from a 1,600 sq ft house in the same area with a 2 ton, so had a pretty good idea that wasn't going to cut it.
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Jun 12, 2007
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London
rocking23nf wrote: this guy was very knowledgeable, he said it would work, I just wanted to get some real life examples from people,
There's a lot factors that are specific to your house - how exposed to the sun your house is and the size/ type of windows/ glass.

For example, my old place had large mature trees that shaded most of the house during the day so I could get by with a smaller unit than my neighbor. Likewise, in my new place, we upgraded all the windows to e-coated glass and the interior solar heat gain dropped dramatically - on many days, we now don't use AC compared to before.

It's quite possible you have giant older picture windows that face south, so you require more AC than normal
Last edited by l69norm on May 13th, 2020 10:36 pm, edited 2 times in total.
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Nov 1, 2010
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Kanata
4 ton is way too big for your house, mine is 2500 and I have a 2.5. While shopping I've read it actually negatively impacts your house. Don't trust what the sales person says.
Uh, yeah, I'd like to speak to a Mr. Tabooger, first name Ollie.
Sr. Member
Oct 17, 2002
948 posts
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Oakville
Sounds a bit too big. Had the resident RFD hvac guy do an install last year when we moved into our current home. Detached house 2800sqft. Had a 3tonne AC installed. It's ok, but in hindsight I should have went with a 3.5.

So I'd say 2.5 - 3t would be good for your size house.
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Mar 23, 2009
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KennyX wrote: Sounds a bit too big. Had the resident RFD hvac guy do an install last year when we moved into our current home. Detached house 2800sqft. Had a 3tonne AC installed. It's ok, but in hindsight I should have went with a 3.5.
Why? Does the 2800 square feet include basement? Does it run all the time on the hottest days without adequately cooling the place? Is your ducting sufficient for your house? In a lot of homes, the ducting (esp. cold air returns) is insufficient to accommodate proper cooling.

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