View Full Version : HELP-getting a new AC unit ?'s on ton and seer amounts

05-25-2010, 04:52 PM
Hi I am very confused. I have a 1800 square foot house with full windows along the back. I am looking at having to buy a new unit. One person says 13 seer 3 ton is enough. Another says 16 seer 3.5 ton will do it. The price difference is about 800.00 and the unit brand is Carrier. Also anyone know if you have to upgrade the furnace for the tax credit? Thanks:goodvibes

05-25-2010, 05:10 PM
To get the tax credit you have to have the higher SEER but in Michigan you don't really need that amount of SEER. The payback usually doesn't justify the extra cost. You do not have to upgrade your furnace for the tax credit (that's a separate credit). I would call at least two more HVAC companies for prices even if it is not Carrier equipment.

05-25-2010, 05:15 PM
Thanks so far for the replies. I forgot to add that I live in Michigan and I got 4 quotes total and they range from 2200.00 for 13 seer 3 ton to 3799.99 for 3.5 ton 16 seer. Brands are Armada, Carrier. One company says yes to credit, three said no. Help!!! It is hot here now... 2999.00 for 3.5 16 seer.

05-25-2010, 05:22 PM
Make sure the price for the 16 SEER is before the tax credit. Some companies quote the price after the tax credit and that can be confusing. Get the price in a written quote. The 13 SEER do not qualify for tax credits.

05-25-2010, 06:27 PM
That price is before the credit. Which would be the better buy? 13 or 16? Thanks so much!!!

05-25-2010, 07:01 PM
The SEER rating is the effeciency of the air conditioner and the number of tons is the cooling capacity.

For the SEER rating, higher is better. A 3 ton 13 SEER unit and a 3 ton 16 SEER unit will both provide the same amount of cooling, but the 16 SEER unit will use less electricity and cost less to run in the long run. You want as high of a SEER value as you can get and pay attention here because you probably will have to be above a minimum level in order to qualify for energy credits.

The number of tons is a little more tricky. The higher the number here the more cooling power the unit will provide, so you might think that more is better, but that is definitely not the case. If you have a unit that's rated too high for your house then it will cool the house down very quickly and only run in short bursts. This will cause more temperature fluctuations and also higher humidity levels in the house making it feel warmer than it is. Since the AC dehumidifies the air as it runs ideally it should be running for longer intervals. However, getting a unit that's rated too low will cause the AC to run almost all the time and it will use too much electricity. Additionally it may not be able to cool your house properly on the hottest days.

There are some standard calculations that a good contractor will use to determine the proper size AC for your house based on your window size and your sun exposure and the size of your rooms... this can be a bit involved to figure out so some contractors will just guess without actually running the numbers. This can lead to an incorrectly sized unit. If you already have an air conditioner that you've been happy with, then your new one should be about the same size (number of tons), but have a much higher SEER rating. If you're getting quotes for a different size than you have now you should definitely ask them why they're quoting that size. It might just be because that's the one they have left over in the back of the shop.

05-25-2010, 10:46 PM
one more question. My husband tells us that our furnace might not be efficient to run a larger seer unit. Is this true? Our house was built in 1998. Thanks:goodvibes

05-25-2010, 11:16 PM
DH is an HVAC guy and repairs and installs AC units in the summer. He said to determine what size unit you need on the tonnage side you need to divide the square footage to be cooled by 500 or 550 depending upon how much sun you get the more sun, the larger the unit you need. Based upon the size of your house the smallest unit you need is 3.5 tons.


05-26-2010, 08:24 AM
Subscribing....we are going through the exact same situation with a very similar size house here in MA. (quoted both 2.5 ton and 4 ton???)

One comment mentioned from both of our quotes was that we needed the 16 Seer for the tax credit and also from our elec. dept but based on living in MA and using it for only a 1/4 of the year we probably wouldn't make back the $$$.

If we lived in a different part of the country and it ran more it would be worth it. I would imagine that is similar for you being in Michigan.

For us the jump from 13 to 16 is huge...if it isn't for you it's probably worth it.

We are finding the issue of tons to be much trickier as well.

Best of luck.

05-26-2010, 09:29 AM
one more question. My husband tells us that our furnace might not be efficient to run a larger seer unit. Is this true? Our house was built in 1998. Thanks:goodvibes

An air conditioner has two parts... the evaporator (which gets installed inside near your furnace, but isn't part of your furnace) and the condenser (which gets installed outside). These two peices should be installed as a matched set, especially if you're paying extra to get a higher efficiency (SEER) unit. If you put in a newer outside unit and leave the existing inside unit it will operate less efficiently and in some cases even void the warranty for the new outside unit.

It's more expensive to replace both, of course, but it really should be done... especially since yours is 12 years old at this point.

You don't have to replace the furnace at the same time, however a new furnace will be much more energy efficient and if you can afford it then it might be a good idea as it will save you money on future energy bills.