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  1. #1
    I just bought a house in Las Vegas built in 1951. It has a split system of 125kBtu gas furnace (80% AFUE)with 5 ton (10 SEER) condensing unit. The system appears to be about 7 years old.

    The system cannot adequately heat the house on a night where the outside air temperature is 28.

    Apparently the problem is that the two return air grills in the house are vented directly (no duct work) to the crawl space and the updraft furnace is directly mounted over a hole in the garage floor directly above the crawl space, thereby making the entire crawl space the return air "ductwork" for the system.

    I measured the inlet air temperature at the furnace blower to be about 35 on a cold night.

    I have had two HVAC contractors out. Both suggest a whole new system horizontially mounted in the attic with all new duct work and new ducted cold air returns in the ceiling.

    The price for the new systems is heart stopping.

    Apparently no one is willing to run real duct work through the crawl space and attach it to the existing furnace (Why?)

    Can anyone offer another suggestion ??

    Thank you. Happy Holidays.

  2. #2
    Join Date
    Mar 2005
    How much room is there in the crawl space? Is the reason they don't want to do it because it is super tight to get someone into in the first place? If there is at least a couple of feet of room it shouldn't be that bad. If so I'd try another contractor.

  3. #3
    The crawl space is very tight. Having just moved here, I am also coming to understand that black widow spiders are very abundant in crawl spaces here. One contractor mentioned that most flexible duct work is no longer rated for crawl spaces. Crawl space is prone to dampness in winter here.

  4. #4
    Join Date
    Jul 2001
    If you have room, consider this.
    Elevate furnace onto a platform. Should be off the floor at least 18" anyway if in a garage. Plug hole in floor.
    Run return duct up off of platform and into the attic.
    Cut returns into ceiling.

  5. #5
    Join Date
    Nov 2001
    or move the furnace to the attic space and gain more garage room.
    If you try to fail, and succeed.
    Which have you done ?

  6. #6
    Join Date
    Mar 2005
    Couldn't you also plug the bottom and come in from the side of the blower chamber. Why does it have to be 18". Am I missing something here?

  7. #7
    Join Date
    Dec 2004
    Derby City
    Call a Professional in to look at the job. Better yet, call the local code enforcement. This system is NOT that old (approx. 7 yrs. according to the writer.) The air distribution part of this system is nothing you should mess with anymoe than the equipment itself. If there is anything done improperly then your local code official can identify that quickly for you. And, once that is done, you should call someone in to make whatever corrections are necessary. All the best, John
    Everyone has a purpose in life..........even if it's to be a bad example.

    Seek first to understand, before seeking to be understood.

  8. #8
    Join Date
    Aug 2005
    Sarasota Florida!! hot & humid
    You know Newtons law is working over time there. An open return air in a crawl space is taking in alot of unwanted air. The extra air sucked in is then slightly compressed by the blower pushed through the supply as a pos pressuer.

    Here is where Newtons law is working so hard against you. If you had a sealed system ie 100%supply = 100%return no leaks in duct. But rip a big hole in your return duct and unwanted air enters the sealed system. The extra added air is heated by your furnace (bad enough) and as you add positive pressure air to a closed up home it pushes out the heated air through any crack back to the outside from wence it came.

    In other words one retrun air leak is not a solitary leak as it causes another leak of sort pressurizing your house and pushing conditioned air out. My bet is you will see air pushing out of your house when ever the blowe runs. Oh and closing the door wont solve anything as the pressuere finds the path of least resistance (another law we have to follow) meaning every outlet and switch or bad window seal is a leak.

    Experiment Turn on blower only, all windows and doors closed, now stand outside front door open it 1/4" and feel for air movment. Then turn off and feel the difference. If not sure lite an incence and watch the smoke.

    You need a sealed Retrun system to code or not anything is better than nothing.

    [Edited by djsreps on 12-23-2005 at 08:20 AM]

  9. #9
    Join Date
    Oct 2005

    Angry Do it all over again?

    Call a sheetmetal person and have them talk with the HVAC man and get the duct work done right. Or do it all over again.

  10. #10
    Join Date
    Jan 2005
    North Las Vegas
    Originally posted by lakeman1234
    Couldn't you also plug the bottom and come in from the side of the blower chamber. Why does it have to be 18". Am I missing something here?
    I think he is refering to IRC M1307.3 which states appliances having an ignition source are required to be installed 18" above the floor in garages.
    Far better it is to dare mighty things, to win glorious triumphs even though checkered by failure, than to rank with those poor spirits who neither enjoy nor suffer much because they live in the gray twilight that knows neither victory nor defeat. (President Theodore Roosevelt)

  11. #11
    Join Date
    Oct 2003
    las vegas
    having run into several of these in the older sections of vegas, we have for the biggest part installed a rooftop
    gaspak or heatpump metal trunk & flex takeoffs

  12. #12
    Join Date
    Feb 2003
    read lots here about crawlspaces &

    the crawl floor needs to be covered with heavy pvc, overlapped & seams taped -- leave 4+ inches masonry exposed to allow checking for termites, etc. using white pvc, such as a pool linner would be nicer -- reflects light so anyone working down there can see = plumbers, electricians, HVAC, CATV, etc -- consider having perimeter of house insulated below ground or along perimeter of crawl. Be sure the sill plate is insulated between foundation & sill -- check if sill is bolted to foundation = better structure.

    You are lucky to have crawl vs a slab.

    I would sure spend the $$ to have ducting in the crawl vs having ducts above roof & penetrating roof! even at 3x the cost --

    The system will work ok for now, just pulling in undesired moisture & dust.

    BTW, change the filter often, when the filter looks dirty, it needed changed sooner. Get a 5inch thick filter, even if that requires a new holder = ASAP.
    harvest rainwater,make SHADE,R75/50/30= roof/wall/floor, use HVAC mastic,caulk all wall seams!

  13. #13
    I have a 3200 sq ft house with 50/50 basement/2' crawlspace in western Ky. The return uses the entire crawlspace as return. surface is coverd in plastic w/gravel. There are no vents through the brick if I were to run ducting to returns. Suggestions?

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