Determination of tonnages


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Old 08-18-08, 10:03 PM
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Determination of tonnages

I have a question about AC tonnages. I am remodeling a house that was originally built in 1972 and both condensers are very old and need replacement.

The house is a house with three sections wrapping around a pool in the middle...see the image below.

http://i173.photobucket.com/albums/w.../pub/areas.jpg

The west side is a living room, dining room, kitchen, laundry room, one bath and a hallway. The north east corner is a garage and that is not under AC. That part has 1034 SF under air and ceiling is standard 8' tall. It has a 4 ton unit currently. There are 4 returns and 6 supplies connected to the air handler. If I replace the condenser it has to be 4 tons correct?

The east side is 4 bedrooms, 3 baths, 1 hallway and it has two supplies to go to the middle connecting family room. The bed and bath rooms total 1027 SF and ceiling is 8' tall. The connecting family room is 470 SF and has a vaulted ceiling that varies from 9' to 16'.

The problem is the family room is always hot and it seems there is not enough AC there. The condenser there is a 3.5 ton unit and I wonder if I could close off the supplies to the family room, hence cooling the rest of the bedrooms better, and instead, install a wall mount split ductless for the middle family room.

If I do plug the two supplies to the family room, will it make the other rooms cooler? or should I upgrade the unit to 4 tons?

Thanks!
 
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Old 08-19-08, 07:48 AM
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You have to be careful closing off supplies too, and sometimes it may just be best to get a technician to take a look at your existing ductwork.

The sizing of a unit for a house is also done via a Manual J calculation that an installer should, but many times doesn't, do. It is a heat loss/load calc for a perfectly sized unit.
 
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Old 08-19-08, 08:51 AM
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The reason I am asking is that I have already contacted three AC companies (licensed and insured) and they came out and none of them did any calculations of any sort.

I said can you tell me based on my intended usages, what is the right size unit? and they all said I have to have matching units to what is installed there right now and does not matter what the calculations show. None of them even bothered to do a calculation.

I asked them about closing off the supplies to the family room and they said "sure no problem".

It seems to me either they can size the unit by walking around, they are lazy, or they are basically salesman and not technicians, they are there to sell me new units.

If I could hire a real "AC tech" do just do an evaluation of what I have I would.
 
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Old 08-19-08, 02:19 PM
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Id find some more companys. If they don't to a load cal what else will they not do?
 
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Old 08-19-08, 03:04 PM
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Agreed.

You cannot size a unit by just walking around, and putting in the same size that is existing is just another easy way. Just because it is in and seems to be working, doesn't mean it is the correct size for the house today.

I too would find more companies, and visit http://www.hvaccomputer.com, where a homeowner can buy a program to perform their own heat loss/load calculation.

Good luck.
 
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Old 08-21-08, 02:42 PM
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Originally Posted by MiamiCuse View Post
It seems to me either they can size the unit by walking around
Well, in a nutshell, that's how residential HVAC works.

They are also telling you that you should plug in a new unit taht's the same size because that's what the ductwork is sized for. If you increase the size of your AC, you need more air flowing over it. The ductwork in your house is not designed for more airflow.

You really don't provide enough information for anyone to help you out with your problem.

But, generally speaking, the approach of adding a new ductless split system seems like a reasonable idea for the room that dosen't stay cool. However I'm not sure that a large room, with high ceilings, is the appropriate application for a ductless unit.

You might try to rebalance the system, if there are dampers installed in the ductwork (probably right where the individual takeoffs leave the main trunk duct) - close down the other rooms a little bit and make sure the family room is wide open. You could also try closing the registers in each of the individual bedrooms to see if that helps.

Also, consider adding a ceiling fan or 2 to the family room, if they aren't already there (sounds like you have a high end house so you probably already have ceiling fans but who knows).
 
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Old 08-21-08, 05:57 PM
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[QUOTE=Garasaki;1416637]Well, in a nutshell, that's how residential HVAC works.

They are also telling you that you should plug in a new unit taht's the same size because that's what the ductwork is sized for. If you increase the size of your AC, you need more air flowing over it. The ductwork in your house is not designed for more airflow.


Residential does not work this way! Only the fly by night guys would do this. If they care about quality and are a good company they will do a heat load. Everybody else does bad work.
 
 

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