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  1. #1
    Join Date
    Feb 2011
    Location
    Lufkin, TX
    Posts
    24

    Building our own home

    My wife and I are building our own home (subbing everything out ourselved) and are already "in the dry". I have been trying to educate myself as much as possible throughout every step of the process to make sure and choose the right materials and subs.

    We are building just outside of Lufkin, TX which is about 120 miles north of Houston and 170 miles southeast of Dallas. Our house isn't typical construction. We chose to go with metal interior and exterior framing instead of wood and a metal roof. It is a 2400 sq foot single story.

    We are looking at doing 3 1/2" of open cell foam in the walls and 5 inches on the bottom of the roof deck to have a completely sealed system. We designed the house with minimal windows and only a few of them are not shaded.

    After all the reading I've done here, I think we're not going to use either of the HVAC companies we've talked to.

    My head is spinning from all the information I've read in here, but part of what I need to know is:

    1.) How to choose a good HVAC company/contractor?

    2.) Will they be telling me what I should get or need or should I have to tell them?



    For example, if a guy I talk to tells me we shouldn't bring in fresh air from the outside, should that rule him out? Or if someone says a heat pump really isn't worth the extra cost? I know this is a huge decision and want to do it right the first time.

  2. #2
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,750
    Look for HVAC contractors that have experience with foam insulated homes. Those that don't will tend to over size the equipment.

    If a contractor doesn't have experience with foam insulated homes, but tells you he knows that it will reduce the system size by 50% or more. He is probably a contractor to keep in mind as a possible choice to use.
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  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,061
    Quote Originally Posted by jgriggs View Post
    My wife and I are building our own home

    For example, if a guy I talk to tells me we shouldn't bring in fresh air from the outside, should that rule him out? Or if someone says a heat pump really isn't worth the extra cost? I know this is a huge decision and want to do it right the first time.
    Specifically, there are many good a/c contractors that do not understand the need for fresh air and humidity control.
    You need to take charge of the issue. ASHRAE/EPA recommend an air change in 5-6 hours at minimum when occupied. They also recommend maintaining <50%RH for health and comfort.
    I suggest a whole house ventilating dehumidifier is the most practical device to handle fresh air ventilation and keeping the home <50%RH regardless of the occupancy or cooling loads. This is new thinking for most. We are beginning to understand the bad long term effect of inadequate fresh air change and high humidity in the home. Ultra-Aire/Honeywell are a couple of the companies offering these devices. I worked for Therma-Stor who make WH dehus like UA for 15 years.
    Be demanding with fresh air and maintaining <50%RH for health and comfort. We can help a good a/c contractor through their first install.
    Keep us posted on your progress, it is typical.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  4. #4
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,750
    Quote Originally Posted by teddy bear View Post
    ASHRAE/EPA recommend an air change in 5-6 hours at minimum when occupied. They also recommend maintaining <50%RH for health and comfort.

    I don't recall ASHRAE suggesting an air change in 5 to 6 hours.

    There formula for calculating min air change doesn't come out to that.
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  5. #5
    Join Date
    Oct 2003
    Location
    Washington
    Posts
    7,405
    ERV, humidifier, 2 stage equipment, variable speed fans and properly sized equipment and ducting......done!!

  6. #6
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,987

    Thumbs up ASHRAE 62.2

    Quote Originally Posted by beenthere View Post
    I don't recall ASHRAE suggesting an air change in 5 to 6 hours.

    There formula for calculating min air change doesn't come out to that.
    4 to 5 hours for a whole house air change seems to be
    close to ASHRAE 62.2 recommendations,

    2,400 sq foot residence = ~ 20,000 cubic feet

    4 hours ... 5,000 cubic feet per hour ... ~ 85 CFM.
    5 hours ... 4,000 cubic feet per hour ... ~ 67 CFM
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
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    66,750
    Quote Originally Posted by dan sw fl View Post
    4 to 5 hours for a whole house air change seems to be
    close to ASHRAE 62.2 recommendations,

    2,400 sq foot residence = ~ 20,000 cubic feet

    4 hours ... 5,000 cubic feet per hour ... ~ 85 CFM.
    5 hours ... 4,000 cubic feet per hour ... ~ 67 CFM
    Only when it has a lot of bedrooms.
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  8. #8
    Join Date
    Nov 2004
    Location
    SW FL
    Posts
    5,987

    Thumbs up Residential Ventilation rate = one or two small bath fan

    Quote Originally Posted by beenthere View Post
    Only when it has a lot of bedrooms.
    2,400 sq. feet * 8 = 19,200 cubic feet
    6 hours ... 3,200 cubic feet per hour ... 53.33 CFM

    Use 0.01 Floor Area + 7.5 * ( # of bedrooms +1)

    .01* 2,400 sq ft + 7.5 * ( 3 +1 ) =
    24 + 30 = 54 CFM Continuous

    53.33 = 54 CFM .. looks pretty close to me for 8 foot ceilings.
    Of course, many residences have greater ceiling heights.
    9 foot ceiling, one needs ~12% more,
    or 60 cfm per TBs rule-of-thumb ( 6 hours)

    Take your pick for these continuous ventilation rates
    or use greater ( ~ 2 x) for Intermittent ventilation.

    Have timers ( 5 to 15 hours) on bath room exhaust fans come into being a regular practice?
    Designer Dan
    It's Not Rocket Science, But It is SCIENCE with "Some Art". ___ ___ K EEP I T S IMPLE & S INCERE

    Define the Building Envelope and Perform a Detailed Load Calc: It's ALL About Windows and Make-up Air Requirements. Know Your Equipment Capabilities

  9. #9
    Join Date
    Feb 2011
    Location
    Lufkin, TX
    Posts
    24
    You two are among the ones I was hoping would respond to my post. The two contractors that we've talked to so far both said they've got quite a bit of experience with spray foam, but I spent about 4 hours reading on here yesterday and a couple of hours the day before and have learned a lot.

    The first guy we talked to wanted to put a 5 ton system in the house and didn't even do a manual J, so I've ruled him out.

    The second guy supposedly did a manual J (which I hope to see the results of), but said that we shouldn't need a heat pump in a house with spray foam and that he doesn't like to do fresh air intake, but if we insisted on it that he would do it. He also said he'd love to see my findings on the fresh air intake, so I plan to direct him to these forums. For me, the fact that he didn't want to do heat pump and didn't want to do fresh air intake rules him out.

    When I say fresh air intake, I know that there are different methods of accomplishing this (ERV, 6 inch "controlled pipe") and am absolutely hoping for advice in that area. TB, is the device you're talking about an ERV or something else?

    Beenthere, some of your posts a couple of years ago looked like you were more in favor of ERV than a 6" pipe. Is that still the case or would it depend on the area of the country and climate?

    TB, should I just do a web search to find the products made by those companies that will accomplish what you suggest? I know that open advertising isn't allowed here, so TB feel free to PM me if there is specific info you feel I should read about the Ultra-Aire/Honeywell devices you are referring to.

    Thanks so much for your time and advice.

  10. #10
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    TB is an advocate of whole house ventilating dehumidifiers, and for the type of dwelling you have in mind to construct, could be a very good option for you. Tight, well insulated homes greatly increase the need for mechanical ventilation via outdoor air. Most of us don't live in houses like this, but you are intentionally building one like this, so yes, weigh your options. The ventilating dehumidifier gives you ventilation when you don't have a high cooling load.

    In winter, fresh air ventilation won't require dehumidification on most days, but you still need the fresh air. The trick is to introduce enough fresh air without drying the air out in your house. For well sealed homes, the challenge is too keep the air inside them from become too swampy in winter, so ventilating with fresh air alone is a good strategy. In summer, outside of a ventilating dehumidifier, a fresh air intake requires the a/c to run, otherwise it just sucks in moist air from outdoors, which in Lufkin can be VERY moist in summer.
    • 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.

  11. #11
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,061
    Quote Originally Posted by jgriggs View Post

    When I say fresh air intake, I know that there are different methods of accomplishing this (ERV, 6 inch "controlled pipe") and am absolutely hoping for advice in that area. TB, is the device you're talking about an ERV or something else?


    TB, should I just do a web search to find the products made by those companies that will accomplish what you suggest? I know that open advertising isn't allowed here, so TB feel free to PM me if there is specific info you feel I should read about the Ultra-Aire/Honeywell devices you are referring to.

    Thanks so much for your time and advice.
    I recommend a whole house ventilating dehumidifier with time controlled fresh air ventilation as basic equipment for your climate. Limit the fresh air to an air change in 5-6 hours and when the home is routinely occupied. If the home gets dry in the winter, reduce the fresh air or add a humidifier. With only 2 occupants, you may need humidification during the coldest weather.
    Part of the controls on the Ultra-Aire is a fresh air ventilating timer. Also the volume of fresh air is adjustable. Another benefit of using make-up fresh air ventilation is your exhaust devices need fresh air to function. The clothes drier, kitchen hood, and bath exhaust fans all need make-up air.
    Regards TB
    Bear Rules: Keep our home <50% RH summer, controls mites/mold and very comfortable.
    Provide 60-100 cfm of fresh air when occupied to purge indoor pollutants and keep window dry during cold weather. T-stat setup/setback +8 hrs. saves energy
    Use +Merv 10 air filter. -Don't forget the "Golden Rule"

  12. #12
    Join Date
    Feb 2011
    Location
    Lufkin, TX
    Posts
    24
    Thanks Shophound. We have quite a lot more humid days than not...even in winter sometimes.

    Would the devices TB is referring to dry the air out in winter? Are you suggesting I need a dehu as well as some other fresh air vent?

  13. #13
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,086
    The dehu is downstream from the fresh air intake. A damper can be installed so the dehu can either recirculate indoor air to dehumidify it, or take in outdoor air and dehumidify it as it injects this same air into the house.

    What determines if you can use winter outdoor air to dry your indoor air is outdoor air dew point. Yes, you may hear weather people use the term dew point all the time...now you have a practical reason for it. Any time your outdoor dew point is below ~ 50 to 55 degrees F, you can use that air to lower the humidity levels in your home. It's easy to be fooled in winter by lower temperatures and higher relative humidity readings. That's why I say to go by dew point. The threshold I mentioned above makes it a lot easier to determine when you can ventilate with fresh air only with no requirement to dehumidify.
    • 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.

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