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  1. #1
    Join Date
    Jan 2009
    Location
    Atlanta, GA
    Posts
    17

    Enclosing crawlspace, questions about furnace.

    Hi All,

    I need some help/advice. We live in Georgia and we have developed some issues with humidity/mold in our crawlspace. Our furnace is also in our crawlspace, 80% luxaire furnace that runs on propane. We are enclosing/encapsulating the crawlspace which involves a new vapor barrier, insulating the walls, sealing the vents etc. I understand our current furnace can't have air vented in so I will need a new furnace with is a two-way/direct vent, whatever you call it. Here are my questions.

    1.)Do used perfectly working furnaces have any resell value, the unit is about 6 years old.

    2.)I plan on not sealing the vents since the current unit needs combustible air until it is replaced, I have 11 vents in our crawl space, is this adequate air for the furnace? Could I close the vents in the summer when we are not using heat? Im assuming the blower for the a/c doesnt need combustible air. The home is 1500 sq ft.

    3.)After enclosing the crawl would a heat pump be another option also instead of the propane furnace? I don't know jack about heat pumps.

    4.)Ballpark what can I look to spend on a 90/95 % efficient furnace/heat pump including installation?



    Thanks so much for any help,

    Greg

  2. #2
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,680
    That furnace would work just fine with a 6" fresh air brought into the crawl and terminated near the furnace, if you do upgrade to a 90% then I would go with a heat pump/gas furnace combo (dual fuel)

    May be able to get a couple hundred from the old one in classifieds.

    As far as prices on new, everyone's area is different post your City and there may be a contractor here that would be willing to bid your job for you.

    Also may find someone to install adequate combustion air to the existing setup if that's the route you choose.
    You can't fix stupid

  3. #3
    Join Date
    Jan 2009
    Location
    Atlanta, GA
    Posts
    17

    Info

    Thanks for the info, I am in the atlanta area.

  4. #4
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,680
    the moderators are going to ask you to move your email to your profile, something about spammers getting into the network from emails being in posts.
    You can't fix stupid

  5. #5
    Join Date
    Jan 2009
    Location
    Atlanta, GA
    Posts
    17

    Thanks

    Quote Originally Posted by cmajerus View Post
    the moderators are going to ask you to move your email to your profile, something about spammers getting into the network from emails being in posts.
    Thanks for the info, I removed it and put it in my profile.

  6. #6
    Join Date
    Jan 2009
    Location
    Atlanta, GA
    Posts
    17

    Issue

    Quote Originally Posted by cmajerus View Post
    That furnace would work just fine with a 6" fresh air brought into the crawl and terminated near the furnace, if you do upgrade to a 90% then I would go with a heat pump/gas furnace combo (dual fuel)

    May be able to get a couple hundred from the old one in classifieds.

    As far as prices on new, everyone's area is different post your City and there may be a contractor here that would be willing to bid your job for you.

    Also may find someone to install adequate combustion air to the existing setup if that's the route you choose.
    That's my main issue, i'm trying to keep air out as it's condensing on everything in the humid summer. In my opinion venting air in would defeat the purpose. Not that i'm crazy about getting a new unit.

  7. #7
    Join Date
    Aug 2007
    Location
    MN
    Posts
    2,680
    you could always have a motorized damper installed on the intake that opens on a call for heat only. Just make sure they put an end switch on the damper so furnae won't run without the fresh air open.
    You can't fix stupid

  8. #8
    Join Date
    Mar 2001
    Posts
    1,213
    Yup... Cm's got the answer.

  9. #9
    Join Date
    Jan 2009
    Location
    Atlanta, GA
    Posts
    17
    Quote Originally Posted by cmajerus View Post
    you could always have a motorized damper installed on the intake that opens on a call for heat only. Just make sure they put an end switch on the damper so furnae won't run without the fresh air open.
    Excuse my HVAC ignorance, would a piece of pipe/pvc etc connect to the damper and run to an exterior wall for the fresh air? Is this likely to be acceptible via code standards? I think my main goal is not to kill my family with carbon monoxide.. I have read over and over on various web sites not to seal a crawlspace with a furnace that requires combustible air under any circumstances, if you guys are positive i'll go with your suggestions provided a local installer will do that job.

  10. #10
    Join Date
    Jul 2008
    Location
    Alabama
    Posts
    658
    how many contractors have you contacted about the musky crawlspace.

    i advise to get a second opinion. has this comp. shown you where the water is getting in??

    all air handlers/ac coils in crawlspaces sweat. specially down here in the south. i've had good success with putting a dehumidifier under houses and sealing off the perimeter vents
    You're only as good as your customer will allow you to be.........If they want junk, sell them junk, but make your junk look neat!!!

  11. #11
    Join Date
    Feb 2003
    Location
    Huntsville,AL
    Posts
    4,125
    why do you want to suck in air with high humidity?
    your owner's manual should state how much air is needed.

    a Pro can provide the solutions.

    keep the water out from under the crawl;
    downspouts extended 10ft;
    dirt next to house higher by 6inches than 10ft out

    be sure to leave 4" of masonry exposed at the ground inside to inspect for termites, etc.

    read at BUILDINGSCIENCE.com
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  12. #12
    Join Date
    Jan 2009
    Location
    Atlanta, GA
    Posts
    17
    Quote Originally Posted by superd77 View Post
    how many contractors have you contacted about the musky crawlspace.

    i advise to get a second opinion. has this comp. shown you where the water is getting in??

    all air handlers/ac coils in crawlspaces sweat. specially down here in the south. i've had good success with putting a dehumidifier under houses and sealing off the perimeter vents
    I've been told by numerous people I need to enclose/seal the crawl space. Apparently the old theory of venting a crawl space turns out to be a bad idea as the warm air comes in contact with the cool ductwork etc and just condenses. By sealing up the space/vents and installing a higher quality vapor barrier as well as insulating the walls you keep out the warm moist air. They also plan on installing a dehumidifier to condition the air if needed. I was planning on doing everything but sealing the vents since my furnace requires airflow until I resolve the issue and then I will seal the vents. One question I did have is I assume the furnace doesn't need combustible air to just run the blower in the summer correct? The summer is the main issue with the humidity, could I close off the vents in the summer leaving the furnace with little air and open the vents in the winter when I have the heat on? I contacted an HVAC guy this morning about the damper solution and he said that's against code, no sure if he is correct though.

    Greg

  13. #13
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,376
    A 90% furnace that draws combustion air directly from outdoors would be the candidate for a sealed crawl space. If you make a transition over to heat pump, foregoing the propane, you'll need to ensure your electric service to the house can handle the auxiliary/emergency electric heat strips the heat pump will require. You could also go with a propane furnace/heat pump combination, as mentioned above known as "dual fuel", but it would be wise to weigh the cost of this arrangement vs. a 90+% efficient furnace by itself. Since you're dealing with sealing up the crawl space, and want the furnace to draw combustion air through a controlled means (intake piping), the 90% furnace by itself might be more cost effective. Sealing the crawl space and insulating the stem walls is going to help reduce heat loss from the house to the crawl space in winter, so your heating needs might drop a bit. Also, if you include a vapor barrier on the floor of the crawl space, you may also find your house easier to keep dehumidified in summer.

    As for your crawl space sealing discussion, has anyone mentioned installing vapor barrier on the exposed soil in the crawl space? It's one thing to seal off the vents and insulate the stem walls, it's another to handle the water vapor coming from the soil itself.
    • 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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