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  1. #1

    R values in Houston

    I looked at my flexible ducts and they have an R value of 6. Measured the blown in insulation at 12" and I believe you multiply this times 3 giving an R value of 36.

    My question is this fairly typical for this geography? Should I improve on this? I want everything just right before the purchase of units. Understanding cost effectiveness.

    Thanks for any help-

  2. #2
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    R36 attic floor insulation is good for Houston, Texas. As for the ducts, the best way to treat them is to consider ways to reduce heat gain to them, since Houston is primarily a cooling climate. Several approaches are available, ranging from least effective (natural attic ventilation) to most effective (cool roof strategy or insulating the roof deck with foam insulation, the latter of which brings the ducts into air conditioned space). Radiant barriers are an in-between approach, with the foil based options more effective than the spray-on options (which is more like a low-e paint than a radiant barrier).

    What will really make a difference, along with considering one or more of the above options, is how airtight your house is. If you spend money to cool your home, but it ends up leaking out into the sky, where has your money gone? To cool and dehumidify a tiny portion of Houston. The only portion of Houston you want to cool and dehumidify is the part of Houston inside your house, not outside.

    Here's the honest truth...you can spend a lot of money on high efficiency HVAC equipment, but none on your house, and not see a substantial difference in your electric bill each month. You can also spend a fair sum on improving your house thermal efficiency, without changing your existing HVAC, and not only see your bills go down, but your comfort levels go way up. Of course, if you're flush with cash, you can do both and be way ahead of the game. Regardless, by carefully evaluating your options, as well as your finances, such will dictate the best approach for you.
    • 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.

  3. #3
    Thank you for your response. I planned on getting an energy audit. Would this be the right approach? Also a bit more info regarding the attic. It has TechShield radiant barrier sheathing. I contacted RIMA international asking if it would be overkill to install a radiant barrier on the rafters. The answer was yes.

    Currently my units are 12 seer 4 and a 5 ton and they are about to turn 13 years old. The size of my house is 3300 sq. ft. I’m trying to educate myself some before the purchase. I agree with making sure everything is buttoned up!

    I understand there is much to learn which is why I’m here gathering info from people far more intelligent in this field.

    Thanks again-

  4. #4
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    One thing I did not mention in my last post is the coinciding caution about tightening a house up, air leakage-wise. You still need to bring in fresh air, except rather than doing it with a bunch of uncontrolled leaks, as most houses do, you narrow it to a controlled source, such as an ERV, a ventilating dehumidifier (probably best option for Houston), or a fresh air intake on the return side of the HVAC air handler (adds load to a/c, will load up the house with moisture if the air handler blower runs without the compressor also running).

    This is where a competent energy auditor can help. He or she can determine how leaky your house is, where the insulation (thermal boundary) weaknesses are, and what low hanging fruit you can tackle first to realize gains in comfort and reduced utility cost. The important aspect of an energy audit is that it should be very thorough, and that you as the homeowner follow up on its findings. IOW, for an auditor to just say your house is leaky, but not attempt to track down where the leakage areas of greatest concern are, does not work in your favor. You need an auditor that is also part detective...he/she starts the blower door and then goes snooping for clues. And once found, they are identified and recorded so you can go back later and work on them.
    • 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
    Thank you for your input!

  6. #6
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,326
    Measured the blown in insulation at 12" and I believe you multiply this times 3 giving an R value of 36.

    different insulation types have different R-values.
    identifying the type of insulation you have will give you
    clarification on R-value per inch.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

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