Central A/C and attic insulation ?

mustash29 Posted By mustash29, Jun 5, 2018 at 9:10 AM

  1. mustash29

    Minister of Fire 2.

    Feb 6, 2012
    SE CT
    I'm looking to have central A/C installed and contemplating beefing up the attic insulation and could use some recommendations from the Hearth crowd. I may do the insulation myself or possibly have the A/C guys do it.

    House - Built in '96, 1800 sqft tri level, 1450 sqft main level with sunken living room + 350 sqft rec/mud/stove room on a slab. Current insulation is R-30 attic, R-19 walls, R-11 basement. Garage slab is level with the rec room slab and under the bedrooms and has R-19 above the garage/under the bedrooms with R-19 walls & 1.5" insulated steel garage doors.

    Currently my attic has 8" east/west joists with 12" bats of R-30 fiberglass. There is a 12' x 16' area above the master bedroom that is decked out for storage. Before I put that decking down I added 2x4's on top of the 8" joists so the insulation would not get compressed. This area is most likely going to stay as is.

    What I would like to do is beef up the rest of the attic insulation. How much insulation should I add? What kind? and How to orient it (cross hatch i.e. run it north south) ?

    I have 2 options for A/C - to replace the current 12.8 K living room & 8 K master bedroom units.

    Option #1 - 30 K Mitsubishi mini split with heat pump option. This would be an 18 K head for the dining/kitchen/living room (relatively open floor plan) and a 9 K head in the master bedroom. $8.5 K and done in 1/2 day. I don't need the heat pump option. I don't like forced air heat.

    Option #2 - 3 ton fully ducted central A/C with high efficiency air handler & high efficiency filtration. $9.5 K and done in 2-3 days. This is my choice because it will have one or more ducts in all rooms (except the bathrooms & downstairs rec/mud room).

    I currently use oil HWB for shoulder season and a wood stove for most of my winter heating. Hopefully this summer the stove will be put to pasture as I get my wood boiler connected. The wood boiler & storage will do the whole house with a Modine type unit in the garage. A Nyletherm will take care of summer DWH and dehumidify the basement (although basement humidity is not currently a problem with the 2 window A/C units).

    Currently sitting on 9+ cord (mostly oak) with 15 more dead mature oaks to take down due to severe caterpillar damage.
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  2. EatenByLimestone

    Minister of Fire 2.

    Jul 12, 2006
    Schenectady, NY
    How is your house on air sealing? You'll get more bang for your buck sealing the house than adding insulation.

    After it's sealed, I'd blow cellulose on top.
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  3. semipro

    Minister of Fire 2.

    Jan 12, 2009
    SW Virginia
    For option 2 where would you install the air handler and duct work?
    If in the attic, you should consider insulating between the rafters with foam to create conditioned space for the HVAC.
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  4. lml999

    Feeling the Heat 2.

    Oct 25, 2013
    Cape Cod, Massachusetts
    Have you looked into the Energize Connecticut programs? Looks like you may be able to get some insulation and top sealing done very cost effectively. We have a similar program in Massachusetts, and had our attic completely topsealed, 8" of cellulose insulation blown in, and all our incandescent bulbs replaced with LED, for about $1K.

    BTW, if you have CF bulbs in the house, hide them...at least in MA, the program will replace incandescent but not CF. Just saying. :)

    Also, btw, you mentioned that you don't like forced hot air...while I don't have personal experience (yet) I think the mini-split heat pump option will feel different from FHA...no ducting, just a warming element and a fan to move the room air...
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  5. begreen

    Mooderator 2.
    Staff Member

    Nov 18, 2005
    South Puget Sound, WA
    Option 2 will be less efficient due to duct losses. This will especially be true if some of the ductwork runs through a hot attic. The mini-split as a heatpump will save you wood during the shoulder seasons while maintaining good interior comfort. Whether that is more efficient than the HWB depends on your electric costs. If high, just straight AC wall mounts would also be fine.
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