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At what point would you need two ac units in your home? I know most 2-story homes that are recently constructed have a dual ac unit. Is this determined by square footage or some other factor. Also, is there ever a need for a dual unit in a one story home?
Last edited by houstoner; 05-09-2009 at 10:36 PM..
Reason: Thread moved from Houston forum.
well since hubby is in the HVAC biz and sitting right here, I'll try to pass on what he is saying...
2 AC systems in a 2 story home is used to provide the same heat & cooling temperatures on both levels. ( warm air rises, therefore more cooling may be needed there
If you had one system without zoning, the upstairs will often be warmer than down.
Some companies put in a zoning system to monitor each level ,with one AC system, to help maintain the same temperature throughout the whole house.
2 AC systems on a 1 story may be needed if the house is large or the length of the house is very long, or depending on the layout /locations of certain rooms. The largest residential AC system is 5 ton. There are some one story homes that need more 5 tons of cooling.
To determine what size unit is needed, a qualified HVAC contractor will perform a manual J load calculation.
hope that helps you some
Hi
I am in no way a hvac expert like crazyma's hubby is but this is my experience..
1) in our CA home A/C at the time of building was an upgrade, and zoned A/C was an upgraded upgrade...we chose the standard A/C (at first we were not going to upgrade to A/C at all, but 1997 was a super hot summer and we quickly changed our minds...believe it or not, A/C is not a "standard feature" in most CA homes...and if we do have it, we go through all kinds of "changes" stressing about what point comfort overrides costs...I know....pretty dumb...
that being said, since all bedrooms are on the 2nd floor, and of course heat rises, it can still, even with A/C get pretty uncomfortably warm while (trying) to sleep...and I really hate that..
So, we were super happy to find out that our new home in Conroe, TX has not one, but two ZONED A/C units, even though our master suite is on the lower level, and the upstairs, with the exception of the game room and hubby's media room, is just guest bedrooms..and while we will not have super frequent guests, the ones we do have we would like to have comfort in their surroundings
I do not know if the number of A/C units in TX is determined by square footage or ????, but our TX home is just shy of 3500 sq ft...
But since we will be new to Texas, I do not know if this is normal building code, or something the builder opted on their own to be installed in the subdivision as a whole, for marketing purposes or whatever, since it was (blissfully) standard equipment
Hope this helps, or at least steers you where you need to go
At what point would you need two ac units in your home? I know most 2-story homes that are recently constructed have a dual ac unit. Is this determined by square footage or some other factor. Also, is there ever a need for a dual unit in a one story home?
This is just supposition, but what if you wanted two different temperatures in different areas of the house, or for an addition to the house? You would need two units in that example, wouldn't you?
it is VERY important that the HVAC contractor perform the ACCA Manual J calculations to determine the heating / cooling loads of the house..... that way, the system(s) can be sized properly, giving you the best efficiency for the space and your buck.
If you are hot and uncomfortable, then you need a second unit or a bigger main unit. If you cooland comfortable than you do not need another unit. it is a simple test
it is VERY important that the HVAC contractor perform the ACCA Manual J calculations to determine the heating / cooling loads of the house..... that way, the system(s) can be sized properly, giving you the best efficiency for the space and your buck.
You are VERY correct in restating this!! There is no eye balling it, there is no ton per every so many sq feet 'rule'. Every house is different!!
( and there are 'contractors' out there that have no idea what a
manual J is scary thought ain't it)
On the original question, the decision to use two units or not comes down to cost. It's twice as expensive to install two systems vs one. This is why you see most two story homes with one heating/cooling system.
It really doesn't have anything to do with the amount of cooling and heating needed as these systems will scale up and down as needed. However in a two story home, and maybe in some one story situations, it means that you may make one part of the house uncomfortable in order to provide enough AC/heat to another area. For example in the hot South, cooling the upstairs in the summer with a single AC system will often make the downstairs too cold. In the winter the opposite problem exists, enough heating for downstairs will make upstairs too hot. Two independent heating/cooling systems solves that problem.
I would highly recommend two systems if you can afford it. Keep in mind that when it comes time to replace these systems it's also 2x as much to replace them.
At what point would you need two ac units in your home? IN my house it was when my daughter got old enough to complain about the temperatures.
When we moved into our house, it only had one system for both floors, and it wasn't zoned. She was in 1st grade, and didn't know enough to complain when it got very hot upstairs.
If we ran the a/c so the upstairs was cool, we were freezing on the main level, AND it cost a fortune. So we had ceiling fans, etc and she was fine...UNTIL she became a teenager.
Rather than install a zoning system, I elected to install a separate heat pump system for the upstairs. I did this mostly because of the configuration of the existing ducts and return and the ease of putting the unit in the attic over the garage, that is right next to her bedroom. It made it much easier to install, and we can operate the two levels independent of each other.
The short answer is "When someone is uncomfortable and complains".
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scary thought ain't it
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