Well shaded, masonry ranch house. Can I undersize my AC?

SwentasticJuly 24, 2014

We've been asked to choose between a 13 and 16 seer unit for our AC. We've already picked a 96% efficiency furnace, and are now debating going with the higher efficient AC set up as well.

Of course I know nothing of the difference except Barack Obama might give me some money if I buy the more expensive unit (only about $600 more) but I'm not positive we'll get a return on that investment.

We live in Milwaukee. House is a 2000sf 1940s stone ranch with 8 foot ceilings and a full basement with open stairway leading down. We're doing an entire system swap, previously had radiant heat in the ceilings (that's another story) so there's a ton of insulation in the attic. Currently has no AC except a 1-ton window unit in the middle of the house which seems to keep it relatively comfortable when its running but I've also noticed it's not bad when its off either (house is vacant right now and undergoing renovation - I turn on the AC when the humidity gets too high). We have an average number of windows, but they're all large, including three 9-foot sliding glass patio doors. The house is relatively shaded throughout the day.

TL:DR 2000sf stone house has been getting away with a 1-ton window unit for the past 50 years. Can I get away with a 13 seer unit? Are the cost savings worthwhile for a more efficient unit?

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I believe the Fed Tax credits have gone away. May be some tax credits from the state or rebates from your electric utility. You need to check that.

What size does dealer recommend? Typically you would be looking at minimum 21/2 ton system. You want to have your ductwork checked for leakage, size, insulation properties, and adequate returns. I see nothing wrong with a quality 13 SEER model especially the way you use AC in your home. You could expect maybe 10% savings going to a 16 SEER model but doubt it could be justified.


    Bookmark   July 24, 2014 at 12:25PM
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Thanks tigerdunes - i will def look into the tax credits. We had to pull the trigger yesterday before i saw your response and we ended up going with the 16 seer - the HVAC guy is knocking off 10% of our cost for paying in cash so the difference actually ended up being a wash. Since we're having all the ductwork installed new, I'm hopeful they'll be as tight and efficient as they can be. We have a friend with a 10 seer unit and they said their bills are outrageous.

Also, I figure the efficiency of the unit will only decrease over time and we might as well fork over the money now in hopes of saving on utilities in the future when I'm sure we'll be broke over this damn renovation. hahaha I appreciate the input - hopefully we get some tax credits but I'm not holding my breath.

This post was edited by Swentastic on Fri, Jul 25, 14 at 12:03

    Bookmark   July 25, 2014 at 12:01PM
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What size, brand, model did you get?

    Bookmark   July 25, 2014 at 12:03PM
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Payne is the brand, and he's using a 3 ton unit. Not sure of the model. This guy does a lot of work on our rehabs and I think he's pretty trustworthy. We're getting the job done for under $7k including all the ductwork, etc. so I think we're getting a good deal. Plus he insists he's got some paperwork for a tax credit so maybe its something locally here - I noticed the fed credits did expire.

    Bookmark   July 25, 2014 at 1:58PM
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You might want to ask your installer where he came up with 3 tons? Based upon you past experience with your 1 ton unit, your location, and your original question, I don't think your unit is undersized (maybe the opposite).

    Bookmark   July 26, 2014 at 11:10PM
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What furnace model, brand, size?

What Payne model?

You have an AHRI matching number for system purchased?

You should know Payne is a POJ. Sorry but true.

Your pricing is better than the hVAC. Oh well.


    Bookmark   July 27, 2014 at 4:42AM
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We calculated the house at 2.5 tons but bc of all the big windows and the fact that our whole basement is open to the rest of the house we decided to go w 3 tons. We're installing hardwoods throughout so humidity is a big concern for the next few years.

From what I understand Payne is a Carrier brand. We've been working w this guy for years and know where he lives so if it's really a POS he'll have to answer for it. I'm sure if I waited around long enough someone would tell me your brand of choice is junk too. Such is the internet.

It's got a warranty and at some point we've just gotta move forward.

Thanks for the advice.

    Bookmark   July 28, 2014 at 2:58PM
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Payne is not Carrier. Any suggestion that it is is simply false. Yes they are part of the same corporate parent but Payne is much closer to Goodman than Carrier. It is generally considered low end.

Sorry but true.

    Bookmark   July 28, 2014 at 3:13PM
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I work for an engineering company a client of which is UTC - they're each manufactured in the same plant using different parts. I understand how these manufacturers work and am comfortable our choice for the price we've paid. I don't care if the parts came from Mexico or wherever. I also don't particularly care about unions.

Can I assume you're a Carrier installer, tigerdunes? Do you have some information to back up what you're saying? I'd love to discuss this with my installer in case he is really that poorly informed. Thanks.

    Bookmark   July 28, 2014 at 3:34PM
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Nothing to discuss. Some dealers think equipment brands don't matter. Others think it does. I fall in that category. Generally in the industry, Payne is thought of as a low end brand. Go to Google and do a search. Also there is a search function on this site as well as others.


    Bookmark   July 28, 2014 at 4:17PM
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This thread discusses some of the differences.

I think most techs can agree quality install is the most important.


This post was edited by mrjasondude on Tue, Jul 29, 14 at 8:35

    Bookmark   July 29, 2014 at 8:32AM
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I have looked at the product data of the Payne and Carrier models. On paper, the Payne model had the same specs as the Carrier builder grade model. Carrier is constantly adding and dropping models, so I am not sure if this overlap still exists.

    Bookmark   July 29, 2014 at 9:15AM
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If humidity is a problem where you live and you are concerned about new hardwood floors then I wouldn't oversize the A/C unit (even by 1/2 ton). The calculated system size (3 ton) isn't consistent with your experience (1 ton window unit which seems to work reasonably well) or your location. It will likely reduce the temperature in your home too quickly to remove the humidity.

Maybe get a second opinion?

    Bookmark   July 29, 2014 at 11:36AM
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Just for additional info. Google "doeduct leakage" and read for a while. Make sure your ductwork is sealed properly at installation. An average leakage is between 18-42%.

    Bookmark   July 29, 2014 at 11:54AM
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Thanks for all the advice, folks. The brand of the units is a moot point now since they're already at the house.

I'll have to talk to the HVAC guy about potentially being oversized - you still think its oversized given we're actually cooling approx 4000 sf? We will have ducts running in our finished basement, and one duct dead ending in the garage. I think there will be a couple cold air returns from bedrooms upstairs, one in the living room, and another large one in the finished basement.

I'll also do some reading about the duct leakage - if its anything like it is in our current house, we'll definitely need to address it. However in our current house the ducts are 30 years old and weren't taken care of. This will be all brand new ductwork.

    Bookmark   July 29, 2014 at 12:30PM
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Of course, I think the brand selected is a big mistake.

And I think the 3 ton will be oversized. Hope it's a two stage AC condenser.

You have a matching AHRI number on the system to be installed? If not, you should. Post it.

You never did say on the size and model furnace to be installed. Hope no third party coil. What thermostat? New air filter cabinet?


    Bookmark   July 29, 2014 at 1:35PM
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Again, thanks for all your help but we already have the thing being installed in our basement so please be kind with your feedback. I do have to live with this thing. If you have anything of value I can watch for or make sure to ask, please add it. I ran downstairs and grabbed the manuals - this is all I know.

Furnace - PG96VAT

Looks like they're all Payne products. I still need to get a hold of the HVAC guy for the AHRI number. Can you tell me what that refers to? Is that for the warranty?

Everything is being installed brand new as we previously had hydronic heat in the house, no AC. New everything.

I think for the the thermostat we'd like one of those wifi enabled learning ones - like the nest or whatever honeywell sells. Do you have advice on which to pick?

    Bookmark   July 29, 2014 at 2:47PM
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No nest.

Maybe Ecobee or a Honeywell WiFi enabled.

I will check these model numbers.

There should be a size number associated with the evap coil model you listed.


    Bookmark   July 29, 2014 at 4:23PM
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I need the size of the furnace and the size of the evap coil to both verify system is a matching system and to give you the AHRI matching performance efficiency numbers.

The furnace is a two stage var speed model. It will require a two stage thermostat for controlling the stages based on demand not a timer that will always leave you on high stage whether needed or not.

The AC condenser is a single stage model which I suspect is oversized and will be prone to short cycling which is never good.


    Bookmark   July 30, 2014 at 7:07AM
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