Results 1 to 7 of 7
  1. #1
    Join Date
    Jan 2005
    Posts
    18
    Okay.

    I live in Roswell, GA (just north of Atlanta).

    DOE says I should have R48 in my attic. Based on about 7.5 inches of blown in insulation I am guessing I have between R18 and R22.

    I want to pull out the blown in (I am sucker for punishment and I absolutely hate blown in insulation.) and replace it with R30 Kraft faced batts (kraft side down) with a second crossing layer of R19 unfaced batts.

    Overkill? Estimate of $xxxx for attic insulation.

    At the same time I am thinking about replacement windows, estimate of $xxxx for windows.

    I used HVAC-Calc to do a quick calculation of the loads for my current situation (single pane, R22) vs. having double pane replacement windows and the new insulation. I know that it is just a 'loose' calculation, but is seems like the load dropped DRASTICALLY.

    My real question is that I am getting ready to replace a 2.5 ton unit and furnace, and I am wondering if doing all of this insulation work will be worth it? I seems like I can step down significantly in the sizing of the new unit. The current unit is 8 SEER and I want the new unit to be 12-14 SEER, maybe higher.

    Am I crazy, will I be able to recoup the costs over 20 YRs in savings on my electic and gas bills?

    - George

    [Edited by BC1 on 02-18-2005 at 04:37 PM]

  2. #2
    Join Date
    Jan 2005
    Posts
    18
    I was actually hoping that by getting a properly sized, new system, I would be able to control humidity much better and therefore have a inside temp in the summer of 76 (we dress lightly in the summer cause we spend a lot of time outdoors anyway).

    That would give a TD of 16, but we typically see high 90's. Ceiling area is 1400 sq.ft.

    So are you saying that I won't get much benefit beyond R36 for the insulation?

    I think the windows are big problem and I am still undecided.

    To rephrase my question, over the long haul is there a significant savings of 2.0 (or even 1.0) ton over 2.5 ton? The air conditioner runs a LOT in our house in Atlanta, at least 8 months out of the year, probably 9. Is there a significant cost savings in the pricing of units?


  3. #3
    Join Date
    Aug 2003
    Posts
    626
    One of the most cost effective things you can do is to lower infiltration the home, and check your ducts for leakage (if they are outside the thermal envelope). I would recommend a blower door test which cn do both. If there are problems in these areas, correcting these problems will have a quicker payback than the two you have mentioned.

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,370
    This past fall, we placed a layer of faced R30 insulation over the very loose, scattered, old and itchy rock wool stuff blown into our attic 37 years ago.

    Last summer, I pulled our furnace blower wheel and cleaned it. I also installed a VisionPro programmable thermostat from Honeywell and configured it for three setback periods.

    I've been watching our natural gas utility bill, since our furnace is gas fired, and it shows a comparison between this month's use and the same month last year's use, and also compares the average temperature for the month. I'm delighted to see not only comparable temperatures, but a drop of almost HALF in NG consumption. We have 1500 sq. ft. ranch tract house with average construction.

    I also ran HVAC Calc on my house and did a before and after analysis with the insulation. My HVAC system was already oversized beforehand, now it's a ton and a half oversized. I also ran a whole hog scenario on HVAC Calc if I were to change out all the windows in the house with double-pane, warm edge technology, low e glass panes, and the heat load drop was significant, especially in this climate which is humid in summer.

    I would agree with lmtd in that there's likely a point of diminishing returns with insulation thickness to money spent. But with the money we spent so far (not a whole lot considering there was a rebate on the insulation and we did the work ourselves) the savings are adding up pretty quick.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  5. #5
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    1) read @ BUILDINGSCIENCE.com -- you are about to put a vapor barrier in the WRONG place! you have humidity, humidity problems --

    2) price storm windows over the existing windows,

    3) now add awnings or shade trees

    4) install film on the west windows

    5) blown in insulation does a good job of filling all the gaps at the sides of the joists -- why not just add the cross batts?

  6. #6

    Exclamation Insulation type can make all the difference

    As one reply commmented, consider air infiltration of your home before changing your insulation. The spray foams on the market are the best which provide excellent insulation and air infiltration. You can check out a soy based foam at our web site http://www.coler.com. I would not recommend fibergalss for any home due to the air infiltration and condensation issues. The same fiberglass is used in your furnace filter - how does that provide good insulation???

    Jim

  7. #7
    Join Date
    Jul 2004
    Posts
    253
    Originally posted by geocave
    Okay.

    I live in Roswell, GA (just north of Atlanta).

    DOE says I should have R48 in my attic. Based on about 7.5 inches of blown in insulation I am guessing I have between R18 and R22.

    I want to pull out the blown in (I am sucker for punishment and I absolutely hate blown in insulation.) and replace it with R30 Kraft faced batts (kraft side down) with a second crossing layer of R19 unfaced batts.

    Overkill? Estimate of $xxxx for attic insulation.

    At the same time I am thinking about replacement windows, estimate of $xxxx for windows.

    I used HVAC-Calc to do a quick calculation of the loads for my current situation (single pane, R22) vs. having double pane replacement windows and the new insulation. I know that it is just a 'loose' calculation, but is seems like the load dropped DRASTICALLY.

    My real question is that I am getting ready to replace a 2.5 ton unit and furnace, and I am wondering if doing all of this insulation work will be worth it? I seems like I can step down significantly in the sizing of the new unit. The current unit is 8 SEER and I want the new unit to be 12-14 SEER, maybe higher.

    Am I crazy, will I be able to recoup the costs over 20 YRs in savings on my electic and gas bills?

    - George

    [Edited by BC1 on 02-18-2005 at 04:37 PM]
    I spent some time with HVAC-Calc to try to understand where the heatload comes from on a new house we are building (a ranch). Essentially, half the load comes from windows (we are using low-e windows) and another 20% from infiltration. We went with spray-foam insulation on the underside of the roof decking for an unventilated attic and have ICF walls. If you are going to be in your house for some time, the following are some things to consider:

    1) Seal your attic with spray-foam insulation on the underside of your roof decking, particularly if your airhandler/furnace and ducts are in the attic.
    2) Make sure your ducts are correctly sized and sealed.
    3) Reduce other air leaks around the house.
    4) Consider low-e windows or shade the existing windows with trees or awnings.
    5) Recompute your heatload if you are going to replace your AC system so as to have correct sized system and make sure ducts are OK.

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