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  1. #1
    Join Date
    Mar 2009
    Posts
    4

    Best option for heating & cooling finished attic

    We are going to finish off an 800 s.f. attic space. There is a hydro air air handler in the space now that serves the second floor (also 800 s.f.).

    What will be more efficient? Option 1 is upsizing the current air handler and outdoor condenser and using zone valves to provide separate zones for second floor and attic. Second floor now is served by a 2 ton system and works fine. Upsizing takes us to 3.5 ton and we are concerned that it may be too much for just one area when a single area calls and therefore inefficent.

    Option 2 is to just install a separate air handler and condenser for the attic space. The issue is running hot water lines from the basement to the attic as well as ending up with a fourth ahu and condenser.

  2. #2
    Join Date
    Jul 2002
    Location
    Zelienople, Pa
    Posts
    2,965
    Option #2
    How tall are you Private???!!!!

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    34,467
    What Gunny said...

  4. #4
    Join Date
    Mar 2009
    Location
    Candia, NH
    Posts
    44
    I agree, option two.

  5. #5
    Join Date
    Mar 2009
    Posts
    4
    Thanks for the input. Any comments on the efficiency of Option 1?

  6. #6
    Join Date
    Dec 2003
    Posts
    709
    Option 1 should be plenty effiecient if you use a variable drive on the blower and the a/c unit is 2 stage. Then you can use zoning that is compatible with this set up. You dont have radiators I am assuming, just a hot water coil tied in with your blower that goes through the same duct as your a/c. Anyway, if this is the case, you will need zone dampers and seperate duct trunks serving each floor. This is the option I would choose but you will need a very good tech and designer to have this set up right.

  7. #7
    Join Date
    Feb 2009
    Location
    Marlborough, MA
    Posts
    58
    This topic caught my eyes.

    for design purposes....

    if your in the attic, i assume you would have to take in to consideration the heat transfer from the roof in the cooling season would be greater. and in the heating season, you would get heat transfer from floor below?

    so my question would be: would you need a beefier cooling system, and not need as much heat as the same 800 sq ft below it?

    sorry if that sounds stupid.

  8. #8
    Join Date
    Mar 2009
    Posts
    4
    Quote Originally Posted by hivacer View Post
    Option 1 should be plenty effiecient if you use a variable drive on the blower and the a/c unit is 2 stage. Then you can use zoning that is compatible with this set up. You dont have radiators I am assuming, just a hot water coil tied in with your blower that goes through the same duct as your a/c. Anyway, if this is the case, you will need zone dampers and seperate duct trunks serving each floor. This is the option I would choose but you will need a very good tech and designer to have this set up right.
    You are right, no radiators, rather forced hot air using hot water from boiler to the A coil in AHU. Thanks for the input on needing v.g. tech and designer as this seems to be a complex system. Sounds like it will be easier to pull hot water lines from the basement and go through a wall or two to get them up to the attic.

    Thanks for the input!

  9. #9
    Join Date
    Sep 2006
    Posts
    1,253
    Quote Originally Posted by vbs52 View Post
    You are right, no radiators, rather forced hot air using hot water from boiler to the A coil in AHU. Thanks for the input on needing v.g. tech and designer as this seems to be a complex system. Sounds like it will be easier to pull hot water lines from the basement and go through a wall or two to get them up to the attic.

    Thanks for the input!
    I bet you will find it hard to justify the cost of running water lines, separate heating coil and cooling set up. Since that space will need minimal heat I would look at a small mini-split heat pump sized to the cooling load. Without much load on it the capacity to provide sufficient heat down to rather low outdoor temps should be good. Oversizing the system a bit (if you have to) to get enough heat should not be a problem on the cooling side since they use inverter compressors which will modulate down to meet the load.

    Lots of people think of ugly wall mount units when they think of mini-splits, but some manufactures also have ducted air handlers (they are very small). Check out Fujitzu, Mitsubishi, Daikin, Sanyo, and others. I'd stick with the Japanese manufacturers and stay away from the Chinese and Korean units.

  10. #10
    Join Date
    Mar 2009
    Posts
    4
    Quote Originally Posted by mchild View Post
    I bet you will find it hard to justify the cost of running water lines, separate heating coil and cooling set up. Since that space will need minimal heat I would look at a small mini-split heat pump sized to the cooling load. Without much load on it the capacity to provide sufficient heat down to rather low outdoor temps should be good. Oversizing the system a bit (if you have to) to get enough heat should not be a problem on the cooling side since they use inverter compressors which will modulate down to meet the load.

    Lots of people think of ugly wall mount units when they think of mini-splits, but some manufactures also have ducted air handlers (they are very small). Check out Fujitzu, Mitsubishi, Daikin, Sanyo, and others. I'd stick with the Japanese manufacturers and stay away from the Chinese and Korean units.
    I looked at these but am concerned about their ability to move the air around the space so there aren't any hot or cold spots. The 800 sf is a rectangle with three dormers and will be used as a large entertainment. So the concern is getting the whole area cooled properly. THe other potential concern is noise from the blower unit since it will be near our home theatre area.

    Lastly, we are in MA so getting below 32 degrees is routine, and after this winter we spent a lot of time in the 20's. So we're concerned about the cost of switching on the electric strips. Thoughts?

  11. #11
    Join Date
    Sep 2006
    Posts
    1,253
    Quote Originally Posted by vbs52 View Post
    I looked at these but am concerned about their ability to move the air around the space so there aren't any hot or cold spots. The 800 sf is a rectangle with three dormers and will be used as a large entertainment. So the concern is getting the whole area cooled properly. THe other potential concern is noise from the blower unit since it will be near our home theatre area.

    Lastly, we are in MA so getting below 32 degrees is routine, and after this winter we spent a lot of time in the 20's. So we're concerned about the cost of switching on the electric strips. Thoughts?


    Inverter systems produce substantially more heat at lower temps - many down near zero, than conventional heat pumps. Find one that produces the heat that you need for the weather conditions it will be operating. I would be surprised if the space would need more than a few thousand BTUs of heat. It will likely need more cooling that heat. There are several mini-splits will produce that with ease and no reliance on electric strips.

    You should have a heat loss/gain calculation done on the area so you know what size system the space will require. One thing to keep in mind is that calculated load calcs sometimes will not completely factor in the fact that much of the space will get heat from the lower floors and some of the cooling will drop from that space down to the lower floors.

    Some mini-splits can have multiple indoor units connected to one outdoor unit. If you wanted to use two wall mounted indoor units you could have one located on each end of the space and resolve the air flow issues that way. If, like me, you prefer ducted units then the noise issues are completely dependent on the duct design. A properly designed and installed duct system will properly condition the entire space and will not have noise issues.

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