Too Much A/C Tons?

We are doing a gut renovation, and plan on installing ducted 2 zone central a/c. We just received specs for a system that calls for two 5 ton a/c units. That seems like over-kill to us, but we aren’t experts. Our place is a brick 4 story townhouse, 16 ft wide, 40 some feet long. Approximately 720 sq ft interior space per floor. Any thoughts on this?  Thanks!

psp215

in Brownstoner Renovation 13 years and 2 months ago

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ellenlourie | 13 years and 2 months ago

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Manual J is a must for load csalculations, but also one must do assumptions about level of infiltrations. to actually determine infiltrations, ( as they migh be very significant part of the load) blow door test must be done, and it will pinpoint as well to certain areas with large leaks so they can be eliminated. Call Robert Gilbert of Brooklyn Green Home Solutions Inc 718-757-6957, he is BPI certified building analyst, he can help you to determine exact loads, and then you will be able to qualify installer.

edifice-rex | 13 years and 2 months ago

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Just insist on a Manual-J calculation (i doubt whoever proposed 10 tons knows how) it is the best way and will cost very little compared to an over or undersized system. Also since you are zoning look at a two-stage condenser it will be more efficient and more effective. Do some online research it will pay off.

psp215 | 13 years and 2 months ago

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Thanks very much for your comments. Looks like engineer has already lost a ton.

jparnass | 13 years and 2 months ago

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I would also guess that one 5 ton unit should be more than adequate.  As Mr. Steam points out above, you want only just enough capacity otherwise your unit will be constantly cycling on and off leading to all kinds of maintenance problems and wasted energy.    My other comment would be: as long as you are doing a gut reno and have two zones already, why not fully zone each floor?  should only be nominal price increase and will increase your efficiency.

agdipierro

in Brownstoner Renovation 13 years and 2 months ago

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2 tons per floor

steam_man | 13 years and 2 months ago

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You must live in a greenhouse (not a green house) if you need all that cooling. Oversized A/Cs short cycle and fail prematurely just like boilers. Plus they cost you more to run. If anything a condenser should be slightly undersized to the load to maximize it’s efficiency. Do you already have a Mechanical Contractor? If not, please feel free to send me over your plans/specs. We would be happy to provide a proposal.

brucef | 13 years and 2 months ago

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That does seem too much, unless you are a corner building, or unusual in some other way. Many contractors do not really grasp how to perform a heating/cooling load. They build surplus into their calculations, on the mistaken concept that more is bettter.For example, a 2400ft residence would typically (and I say this for example only) be cooled with 4 ton condenser.