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Old 03-03-2012, 10:02 AM   #1
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ac in attic or basement?

replacing retro fit attic installed undersized ac in a 48 year old brick with adequate wall insulation old wood good shape andersen windows and minimal attic insulation very well shaded lot. baseboard boiler hot water heat

ac company recommends moving air handler and ductwork to basement over insulating them in attic. yes or no? will floor vents for ac from basement be better than ceiling vents from attic install?

thanks for any info


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Old 03-03-2012, 10:05 AM   #2
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.................. You gain a bit and loose a many floors is your home?


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Old 03-03-2012, 10:14 AM   #3
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Keeping duct and equipment in a conditioned space is always better than sticking it in a hot attic. Insulation on duct slows the transfer of heat but does not stop it so attic installed will have a greater heat load on the system.
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Old 03-03-2012, 10:15 AM   #4
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Having duct installed in the attic is always a last resort.

Think about how hot an attic gets in the summer time. This heat is a heat gain to the duct and this adds heat to the duct. Thus warming the already cooled air. And just the reverse in the heating season where it would be a heat loss from the duct. Even with an insulated duct you still will have a heat loss/gain

Now, keep in mind that there will be a heat loss/gain with duct run in the basement but the basement temp will pretty much be a constant 65-70 deg. Where as in the summer the attic can reach 125 or higher and in the winter 32 below or lower.

Where would you place the duct?
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Old 03-03-2012, 01:53 PM   #5
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thanks everyone
I'll answer questions and offer a little more here:

this is a single story frame house NO roof trusses approx 2000 sq ft

the idea would be to construct a chase or something like one around the main trunk and blow in a foot or so of insulation and cover the top of the trunk with another foot. same thing for feeder lines (there are seven of them in a 3 br 1 bath brick ranch)
might even build an air handler "room" around air unit with access for service, theres plenty of room in the framed attic
then insulate the attic up to current standards
the idea would be to bring all the attic ductwork and possibly air handler effectively inside the building envelope
there is a large attic fan mounted on the gable end of the house with a 3ftx3ft louvered vent in the hallway, no ridge vent, soffits and gable venting, the new air handler would be mounted in the hall next to the fan vent and thereby have the return air flow directly into the air handler.

the real question I have is with insulating this way and effectively bringing the ductwork into the envelope (if thats possible I realize there's more heat loss/gain no matter) would the overall effect be better than putting the thing in the basement and living with floor vents? Would there be adequate flow and performance with cool air vents in the floor? The ac company that did the heat load calc says yes and that it would be more comfortable than attic install. anyway, thats the question and info
thanks again to all for great responses. any additional comments appreciated
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