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Discussion Starter · #1 ·
Background:


-House house 2 finished levels totalling ~2800sq. ft

-Unfinished basement totals ~1200 sq ft.

-Single A/C unit plumbed to to all all 3 levels for registers

-A/C returns only present on the 2 upper floors (none in basement)


Current situation:


-Even with basement vents closed, the A/C cannot keep the upper two floors cool on hot days

-Initial eval from contractor states that A/C unit is borderline sized for house

-Contractor also believes returns are too small

-Basement relatively unused, but does get warm if a few people are down there, lights and stereo are on, etc..

Goal:


-Finish basement with media room, exercise room, bar area, etc...

- Add heatload in terms of equipment and people, yet stay comfy.

Current thinking:


-Install a second attic-mount A/C to handle the top floor, using existing ducting and return

- Install a basement return, and use existing A/C for "middle" level and basement

Questions:

-Has anybody here done this before?

-Any guesstimates on cost based on the above sq. footage numbers?

-Would there be pro's/cons to this as opposed to just sizing the existing system up?

-Any other suggestions instead?



Thanks.
 

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I'm surprised that you did not have two systems installed from the beginning.

I think that you are on the right track. In addition to a new system for the upstairs you may want to consider a converting the existing unit to a dual zone system which would give you a separate thermostat for the basement and allow it to be cooled or heated independantly of the main floor. You really need to get some input from qualified HVAC installers. You should be able to get a free estimate.
 

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Currently living in a 5,600 sq/ft 1911, American Four-Square...I designed and installed a three zone system for the house (1st floor 2000 sq/ft, 2nd floor 1800 sq/ft and the attic 1800 sq/ft)...not counting the basement. Would highly recommend a separate zone for each floor....it allows you to adjust the thermostat set points on each floor based on the season of the year and the humidity. Works great for my situation. In my case, it's like putting in three different systems, so the cost was equal on all three floors. (About $24K total) In case you are wondering, my HT will go in the attic...someday. As the gentleman said above, get an opinion from a qualified HVAC person.
 

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Discussion Starter · #4 ·
Thanks for the responses thus far.


The A/C was already installed in the house when we bought it at nine months old.


Given that the existing unit is likely large enuff for the basement and mid-level, I'll probably look in to having it dampered such that I can control each of those 2 levels individually, and then have the new attic unit for the top level with it's own thermostat.
 

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Are the second floor supply grilles at the ceiling or the floor?If they are at the floor how are are you going to resuse them?


Can you increase the fan motor speed of the furnace or air handler? What is the maximum volume of air that it can deliver and how many tons is the present A/C?


When the contractor said the returns are to small. Did he mean that they are reducing the load on the machine and resulting in icing up of the evaporator. If the machine is too small or overloaded, the amperage draw of the compressor will be at full load amps, and the suction pressure will be running high above 45 degrees saturated suction temperature. If these two items are not in that range then open the return duct and see if you can increase the load on the machine. A restricted return will cause a low CFM delivery.


Are the ductwork joints sealed? Is all the cold air going to the upper rooms or is it leaking into the basement?


What type of metering device is being used for the refrigeration circuit, a TX valve or a orifice piston? Tx valves keep the evaporator coil fully flooded at all times, piston's do not.


If the A/C unit is truly undersized, it would probably be cheaper to upsize the main A/C (providing that the furnace fan can deliver more air for the larger machine) and possibly install a zoning system for the whole house. Installing attic mounted A/C is never cheap, it is hot itchy work. You will need to install a air handler with insulated ductwork, a condensate drain, power to the unit, refrigerant lines down to a new condensing unit that will also need power run to it. Replacing the existing unit you might be able to reuse the power wiring and refrigerant lines, just change the evaporator and the condensing unit.
 
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