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  1. #1
    Join Date
    Jan 2013
    Posts
    12

    Question Too Small of Furnace?

    Background info:
    Northeast of Seattle
    2004 built 2 story, crawl space, master on main, a little under 2100 sqft, typical track home build

    I just purchased this home in early October and have not been really happy with the current Bryant 310AAV, 44k Btu, 80% LP gas furnace. My main complaints is that it takes roughly 3 to 4 hours to warm the house from 65 to 69 degrees and that the air coming out of the registers is lukewarm at best. When the system is on (averaging about 9 hours a day, up to 13 hours when the temp was in the mid 20s), at the closest register to the furnace I am only getting roughly 90 degrees of warm air out of it. Most of the time it feels like the house has a cold draft when the system is running.

    I set my thermostat to 69-70 when I am home (mornings, evenings and weekend) and set it back to 65 when I am gone and at night. Normally I like to set the thermostat to closer to 62 when I am gone and at night but the, what I feel is, slow recovery time makes it unreasonable. I’ve had the furnace serviced right after I purchased the house.

    Comfort is very important for me and I am contemplating adding an AC unit for those few weeks that are warm and would also consider replacing the furnace at the same time if it is undersized.

    From reading the forum so far I realize that I need someone to perform a Manual J calculation on my house to properly determine the correct furnace size, but judging by this limited information I presented, do you feel that this furnace is undersized? Any advice or opinions would be greatly appreciated!

  2. #2
    Join Date
    Jan 2004
    Location
    PA
    Posts
    68,803
    More like something is wrong with it. An under sized furnace would still blow out warm/hot air, just not enough of it to heat properly.
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  3. #3
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,905
    the unit probably was not converted properly ,call a trusty service company or your propane provider to come check it as this is a job for a pro
    We really need change now

  4. #4
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,240
    Surprise

    A couple of observations and questions.

    I assume nat gas service is not available. You should recheck your furnace's model number for accuracy including input and output BTUs. It probably has an output of 48 KBTUs, not 44 K.

    You may not have enough extra capacity to handle your setback and recovery in a reasonable time.

    Your furnace is not that old. When you were purchasing this home, did you ask an HVAC pro to come out and check system? It is something that I would recommend for all potential buyers to do before purchasing an older home. The low supply temp is a symptom of a problem. It should be triple digits. I would
    want to know if furnace had the propane conversion kit installed that most furnaces require. This should be checked.

    Drafts are not necessarily a problem related to furnace operation. When furnace is running normally(not on setback/recovery), what is a typical run time?

    I would definitely have your furnace checked out thoroughly and preferably by a Bryant dealer.

    And if considering adding AC at a future date, then look into adding a nice 13 SEER heat pump. It would save you on propane costs.

    Keep us posted on your action plan and what you find.

    IMO

  5. #5
    Join Date
    Jan 2013
    Posts
    12
    First off, thanks for the replys!
    I had a typo, the system is a natural gas system not LP. Sorry about that!
    The sticker on the unit indicates that it is a 44kBtu input, 36kBtu output unit model number 310AAV036045AAJ.
    Typical 68 to 69 degree run time is roughly 30 minutes.
    I've had an Angie's list A rated company out to do a yearly maintenance on it in October and they said everything looked good. I also had a tech come out near new years to replaced the hot surface ignition thing and he also said everything looks good. So I'm at a lost to what's wrong.

  6. #6
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,240
    Surprise

    Well that is a heck of a big difference as far as size of furnace and the fact that it is nat gas and not propane fuel.

    Even at that, that is a very low supply temp which suggests burner should be checked as well as a leaky ductwork system. You should be getting triple digit supply temp on a non condensing furnace that you have. You may be undersized but still that low supply temp points to a problem. You should check that supply temp again at different supply registers in your home.

    Any idea of your nat gas rate/therm and electric rate/kWH?

    IMO

  7. #7
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,122
    Cannot believe that anyone here feels a 44k Btu 80% furnace in a 2 story home that's 2100 sq ft in Seattle is sufficient.. I sure am glad most of us a/c and heating contractors in Houston have not drink the "To Big" Kool-Aid. We never have the systems to big or to small complaints here.
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

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  8. #8
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,240
    Not necessarily disagreeing with above post. But it should be noted that for PNW location of OP, it has a relatively mild winter and summer. I do understand though that there can be extremes for both seasons. I would think though since this thread focuses on heating and furnace size, that the average winter temp low is most likely in low 40s which surely this furnace can handle even in setback recovery. However, the long recovery times are on the extreme lows which would seem normal to me. OP should be happy that he is even getting recovery back to his thermostat setting.

    Still the low supply temps suggest a very real problem that needs to be addressed.

    IMO

  9. #9
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,122
    __________________________________________________ _______________________
    “Experience is a hard teacher because she gives the test first, the lesson afterwards". - Vernon Law

    "Never let success go to your head, and never let failure go to your heart". - Unknown

  10. #10
    Join Date
    Apr 2011
    Location
    SE Washington
    Posts
    559
    we are in eastern washington and just by your post, it seems a little undersized for the square footage, a 60000 would have been more in line, however, without a proper load calc we are just guessing, the low outlet temps are more in line with a heat pump, somethings amiss!, where is the ducting located, is it insulated?, is it sealed?
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  11. #11
    Join Date
    Jan 2013
    Posts
    12
    I'm outside of Seattle, so I'm just a little different. Average January low temp is 33 degrees and roughly 5000 heating days, well from my limited research anyway.
    I'm checking temps using a simple indoor/outdoor probe unit, so probably not the best. The sticker on the unit states that air temp rise should be 20 to 50 degrees, so assuming that the indoor air is 69 degrees wouldn't 95 be appropriate? Could the blower motor be set to produce too much cfm? WOuldn't that result in the lower specs that I am seeing?
    I just checked my gas bill for 12/15 to 1/15 (I was gone for a week, and the unit locked itself out due to the no ignition fault that was repaired when I got home), 121 therms were used at roughly $1.00 per Therm.
    Electricity is tiered but it approximately $0.09 per KWH. So if I did the conversion correct $1 of NG is equal to $2.7 of electricty.

    Is checking the duct work in the crawl space something that I normal person can do? Is this something that I can get the Bryant repairman to do for a reasonable cost? What should I tell them, when I make an appointment?

  12. #12
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,240
    for Mr Bill

    Good info you posted on Seattle. Those record highs and lows are very interesting. Of course, one should size to the average with some fudge factor percentage both heating and cooling.

    Best Regards..

  13. #13
    Join Date
    Mar 2006
    Location
    The South
    Posts
    2,240
    Surprise

    You need to recheck your supply temps at various rooms in your home. Note outside temperature. Obviously if you are still getting 90 degree supply temp, the ductwork should be checked. You can do that visually for any obvious problem but in fact a repairman should have the necessary equipment to make a better check. Your blower fan should be set to 400 CFMs/ton. Burner should be checked out for any adjustment. Repair tech should not be satisfied until you are getting 100+ degree supply temp.

    Perhaps others have some other ideas.

    IMO

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