1.5 ton for 600 sq ft?

Old 04-17-07, 04:09 PM
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1.5 ton for 600 sq ft?

I am in the final stages of planning for a complete replacement of my very dated HVAC system. Our 2200 sq ft home was designed and ducted for heat only in 1962 and AC was added later. The upstairs remains very warm. After talking to 7 contractors and getting multiple bids the plan is to replace the downstairs with a heatpump and add a second unit in the attic to handle the upstairs as all the ductwork is in the wall and would require too much plasterwork to redesign.

Our upstairs consists of a landing, two bedrooms, and a small bathroom. Total sq footage of about 600-700. The two options that have been presented to me are installing an LG mini split system or a 1.5T system with a VS airhandler and new ductwork in the ceiling. I would prefer to stay away from the mini split system.

Here is my question. My chosen contractor (who I have checked out extensively) suggests that although the 1.5T it too large that it is the smallest central air option. He plans to use a 2T vs airhandler and adjust the dip switch accordingly. He also suggests "dumping" some excess air in the attic and with vents angled to go downstairs. Does this make any sense? It seems that I'm just going to be running the upstairs system to cool the attic. I realize there are limited options for a separate system upstairs but this much oversizing concerns me, especially after reading so many posts on this page warning against it. What do ya'll think about mini splits?

Old 04-18-07, 06:19 AM
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I certainly wouldn't entertain the idea of 'dumping' air into the attic. Not only are you paying to keep the attic cool (and risking condensation issues), the unit will then replace that air any way it can, buy sucking it in from outdoors through every crack, hole and crevice in your home that it can find.

So you get to pay twice, first to cool the attic, and then again to cool the unconditioned outside air it has to pull in to replace what's being put in the attic.
Old 04-18-07, 08:28 PM
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The installer sounds innovative to me. Using standard equipment to properly cool and dehumidify small spaces is extremely challenging.

Of course a customized system could be designed and built to fit any size space but it would be expensive to build and would not have the government-mandated energy efficiency (SEER) rating and it would require a very competent tech with knowledge of the original design to do any servicing on the unit.

Rather than "dumping" some of the output of the attic unit into the attic it would be worth it to try to install some small, insulated ducts from the attic system through the walls (most likely interior) and dump this excess into the lower level. Since the volume of this "dump" air would be relatively small you could use the small ductwork that is used for a Unico high-pressure system. The (again, relatively) small volume of conditioned air from the attic system should not have an appreciable negative effect upon the downstairs system.
Old 04-19-07, 09:47 AM
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I take it that the upstairs unit will have a small heat element in it also . For sure you dont want to just blow air from the home in the attic. The attic needs it own vents for in and out air up there. Id say a 1.5 ton Ac for that up space will work ok. if you think about it a lot of that cool air will fall to the down stairs anyhow. Id let the Dip switch as is for the 1.5AC and with that V/S blower be sure and put in the humidistat control on it that will slow the blower down when need be. I think you will find that this set up will work just fine

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