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  1. #14
    Join Date
    Jun 2000
    Location
    WYO
    Posts
    2,019
    your "trigger" point is the heat anticipator setting. Have a tech check this, that and other settings . A good one can do this in 1/2 hr or less & check on sizing. High eff. units can be set as much as 25% over antic reading.
    never say never

  2. #15
    Join Date
    Jan 2005
    Posts
    9
    Originally posted by hvac-tech-lane
    Does the furnace that is suposedly "too small" keep up or does it run continously and loose control (space temp drops) if not it is not too small.
    It has what I consider long run times, 40 - 50 minutes, can go off for 5 - 10 minutes, and then go right back at it again. So I would charactarize it as "barely keeping its head above water". I hear you, I am making a comparison to the front big furnace, and may be assuming that the "small" back furnace is not configured right. I did get opinions on this one too. I have been able to settle it down by having anticipation be longer, 2 - 3 degrees. I can get almost 40 minutes between cycles with not much longer runtime. I track the actual on time of the unit when it draws power, and this technique has the furnace running about 5 hours less a day with my family not noticing. so far...

    Its march now, I dont think this will work on the coldest days. Since the space open to the front big furance, I think some heat is coming across from that side of the house. Overall though, my runtime for both furnaces is down per day. I am translating that into less gas being used, the bill will prove that..

    The other challenge for the "small" back furnace is that almost all the ducts go over an unheated crawlspace, or up outside walls. So the furnace spends the first 5 minutes warming the ducts back up. It takes almost that long to feel that the air is warmer than room temp.

    Can ducts in crawl spaces be insulated? Its that a good idea?

    Paul

  3. #16
    Join Date
    Apr 2003
    Location
    the Great Pacific Northwest
    Posts
    607
    "Can ducts in crawl spaces be insulated? Its that a good idea? "
    Absolutely as a mater of fact its not only the proper thing to do but its code where i'm at and I would believe everywhere now. If you do insulate your ducts you will need to use insulation with a vapor barrier made for insulating duct. Also sealing your duct work at all the joints is a good idea using duct sealing mastic.One caution about tightening up a crawl system be alert to the potential that exposed pipes could now freeze.

  4. #17
    Join Date
    Feb 2005
    Posts
    40
    you might look at the location of the T-stats. I found one that was 6'3" above the floor. Are they in the proximity of their respective units. Check for air flow through the t-stat wire hole in the wall behind the stat, plug it if there is one. I had one that would never reach set point because of the hot air being pulled through the wire hole. The center of the room would read below set point,(in cooling mode). Are they located on the interior walls or an exterior walls. You might check the blower speeds on the units. And, just out of the wild, clear, blue yonder, is there any chance that the units are connected to the wrong or oppsite areas that they were intended for. I have found that to be on a multi-install systems. Had several units in one mechanical room, with two of them going to the wrong area. The big unit was suppling to the smaller area and vise a versa. Just asking questinons,picking your brain with a bunch of what ifs. Sometimes it the simplest and dumbest things that make you pull you hair out.

  5. #18
    Join Date
    Jan 2005
    Posts
    9
    HVAC-TECH-LANE- OK. Good input and that looks like a project. I understand about the freezing, i have run into that at another house closing off the crawlspace to the house space. Water pipes froze right up, but putting the foam around them fixed that.


    Originally posted by rudeman
    you might look at the location of the T-stats. I found one that was 6'3" above the floor. Are they in the proximity of their respective units. Check for air flow through the t-stat wire hole in the wall behind the stat, plug it if there is one. I had one that would never reach set point because of the hot air being pulled through the wire hole. The center of the room would read below set point,(in cooling mode). Are they located on the interior walls or an exterior walls. You might check the blower speeds on the units. And, just out of the wild, clear, blue yonder, is there any chance that the units are connected to the wrong or oppsite areas that they were intended for. I have found that to be on a multi-install systems. Had several units in one mechanical room, with two of them going to the wrong area. The big unit was suppling to the smaller area and vise a versa. Just asking questinons,picking your brain with a bunch of what ifs. Sometimes it the simplest and dumbest things that make you pull you hair out.
    Those are all good points. I am pretty shure about the stat placement, I know they are in the areas they service. They are both on inside walls. They are clean (brand new). Before I put the new ones up, I hung them on the wall by the old ones (12 year old honeywells) and discovered that the honeywells tripped at 1 degree anticpipation. I can change that on the new ones, and they have relays so I could watch how they behave before I switched over.

    A lot of other things for me to investigate and review with my local tech. Thank you!

    Paul

  6. #19
    Join Date
    Apr 2003
    Location
    the Great Pacific Northwest
    Posts
    607
    Originally posted by pbibm
    HVAC-TECH-LANE- OK. Good input and that looks like a project. I understand about the freezing, i have run into that at another house closing off the crawlspace to the house space. Water pipes froze right up, but putting the foam around them fixed that.



    Paul
    Finer point on pipe insulation: Insulation slows thermal transfer, thus an insulated pipe will merely take longer to freeze " Howcome my pipes froze an broke while I was on vacation I insulated all of them."

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