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Thread: Old Payne furnace advice

  1. #1
    DIY Junior Member sdmarkus's Avatar
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    Default Old Payne furnace advice



    Not sure this image does it justice, but I have this monstrosity of what seems to be a very old Payne furnace in my garage.

    Any idea where I might find the model number and some additional information on this beast? Trying to decide if this unit is salvageable or needs to be removed in preparation for a newer more efficient furnace or HVAC system.

    Does the old fiberglass covered ducting need to be replaced regardless?

    Thanks in advance for any assistance you may be able to provide.

    -Mark
    Last edited by sdmarkus; 06-26-2011 at 01:13 PM.

  2. #2
    General Engineering Contractor ballvalve's Avatar
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    Biggest danger in a very old unit is that the heat exchangers burn thru and you get combustion elements into your house air. Have it well inspected.

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    Forum Admin, Expert Plumber Terry's Avatar
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    I can attest to that.
    My previous home had a perforated heat exchanger, and the one I'm living in now needed replacement before I could move in.
    They only have so many years in them before they become dangerous to your health.
    The headaches before we figured out the problem were not fun.

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    Plumber jimbo's Avatar
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    SO, for starters, make sure you have a CO alarm in the house ( now law in many places)

    If you remove the front cover, there should be a data plate. I can tell you the date from the serial number.

    If the unit is otherwise working, the heat demand in So. Cal. is not high enough to justify a new unit, especially an expensive high efficiency unit, unless it really needs to be replaced.

    Check that all the insulation on the ducts is intact, and check for air leaks at the joints.

    IMPORTANT note: DO NOT run the furnace for any length of time with any of the front covers removed, because you can draw combustion products into the air stream. Replace the filter often for efficiency.

  5. #5
    General Engineering Contractor ballvalve's Avatar
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    And use radiant heat with the heater outside. Now you have solved all the issues.

  6. #6
    In the trades Dana's Avatar
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    Quote Originally Posted by sdmarkus View Post
    [IMG]

    Trying to decide if this unit is salvageable or needs to be removed in preparation for a newer more efficient furnace or HVAC system.

    Does the old fiberglass covered ducting need to be replaced regardless?

    Thanks in advance for any assistance you may be able to provide.

    -Mark
    Seriously, if this beast is over 20 years old (and it may be old enough to qualify for an AARP card :-) ) any money spent on maintainning or repairing it is wasted. If history is any guide it's probably at least 2x oversized for your design day heating load (likely more), and is probably running under 70% efficiency, even if it's as-rated AFUE the day it left the factory was 78%. If your AC of similar vintage & condition that too needs to be looked at with a jaundiced eye.

    With a zip code (for weather data) and a heating-season's worth of gas bills it's possible to figure out what a "right sized" gas furnace would be. In many SoCal homes even a smallest-in-class condensing furnace may still be oversized, in which case a variable speed R410A-refrigerant 16-18 SEER heat pump for both heating & cooling might be the better investment. (If yours is an open floor plan odds are you'd get a coefficient of performance of ~4 or better during the heating season using a ductless split system, which would be cheaper to operate than condensing gas (even if you sealed the ducts), and way cheaper to operate than a ~70% efficient gas burner located in an unconditioned garage. With a ducted heat pump your COP would drop, and you'd have duct leakage losses, but most would still be operating-cost competitive with condensing gas.

    As long as the ducts are air-tight, the small amount of surface damage/wear on the insulation isn't much to be concerned about. The lack of mastic-sealant on the galvanized ducts (particularly but not exclusively the el below the fiberglass insulated duct) is an indication that unsealed ducts are probably wasting double-digit fraction of the heating fuel being directed somewhere else, while sucking up garage fumes and creating pressure differences between rooms that drive air infiltration rates. IIRC CA Title 24 requires duct leakage testing & remediation to some limit whenever HVAC equipment is replaced/commissioned, as well as some maximum oversizing fraction on a Manual-J type heat gain/loss calculation (which is easily & often fudged to the high side even by well-intentioned contractors.) Whether you keep the ducts &/or furnace or not, sealing all joints & seams the ducts and taping every seam on the furnace with FSK tape is a good idea.

    The burner on the gas HW heater visible on the edge of the picture is probably big enough to cover both space heating & hot water using an air handler with a hydronic coil, which may be cheaper and would as-efficient as replacing the existing unit with a right-sized 80% AFUE heater. With a hydronic coil & air handler the leaking heat exchanger problem simply doesn't exist. (eg: http://www.firstco.com/products/aqua_therm.asp or http://www.pmpairhandlers.com/ or http://www.ableair1.com/pdf/apollo_brochure.pdf) At a later date when it's time to replace the water heater, a condensing tank (or tankless) HW heater could also still be used, and efficiency would be quite high. Air-handler type combi-heat/hot-water is a pretty straightforward & simple solution using plain-old standare HW heaters when design condition heat loads are under 25,000 BTU/hr, which is common in SoCal. The raw combustion efficiency of a plain old tank heater is ~80%, and since you're already paying for the standby losses on the water heater, raising the duty cycle by putting that burner to use for space heating only increases net efficiency. It doesn't take much of a coil or air handler to deliver 25KBTU/hr with 125-140F water, but you still have to do the math on it. Overdesigning for actual loads can still be cheap to implement, but with too large a coil you can end up shortening the lifespan of the water heater (due to excessive condensing-mode operation). If done as a DIY, design it, don't hack it, and the water heater will last as long as any.

    BTW: The galvanized fittings it looks like someone retrofitted on to the gas lines wouldn't pass a code inspection many places, and used to be banned nearly everywhere (not sure about SoCal.)

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    DIY Junior Member sdmarkus's Avatar
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    Dana, thank you for the wealth of information. The air handler concept sounds very interesting and something I'll definitely research further.

    Jimbo, would the model number(800019A) tell you anything?

    Here's an image of inside the cover, not looking too good eh?!


  8. #8
    In the trades Dana's Avatar
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    On the plate behind the gas valve in the middle of the picture they probably have the input & output BTU specs, as well as the date of manufacture stamped in there somewhere. Take notes- and share!

    At least it's only a 3-tube burner- it might be only 3x oversized for the heat load. :-) Given the amount of visible rust it's unlikely to be hitting 80% steady-state efficiency, but it's remotely possible (or might be revivable to approximately that with a burner cleaning.)

  9. #9
    Plumber jimbo's Avatar
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    That does not seem to be a model number...not found on Payne ( Carrier Epic website).
    One way or another, I would replace the brass flex, because those old brass ones were prone to failures.
    That gas valve looks pretty old. I would be concerned about rust-through on the heat exchanger. Since a furnace is relatively cheap I would be leaning towards replacing that puppy.

  10. #10
    In the trades Dana's Avatar
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    I'd have to agree jimbo- everything about it looks old enough to say "pitch it". Even the tiny 2-stage ~95% efficiency condensing variable-speed blower Goodmans are under $1500 f.o.b. the distributor's warehouse (not including installation), which would maximize comfort & efficiency, even if oversized for the load on the high-fire end (which is likely.) Even if your heating loads are so low it doesn't have payback in fuel & power use over a mid-80s efficiency model, the ultra low noise plus comfort of the variable-speed units is worth paying for, and it may not be dramatically more expensive than a hydronic air-handler solution that only runs at 75-80% efficiency off the water heater.

    But let's see if you can't right-size it. What's your zip code (for weather data), and what is the heating season fuel use?

  11. #11
    DIY Junior Member sdmarkus's Avatar
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    The serial number should be DGGB 32441 with an input of 80.000 BTU/HR and 64,000 BTU/HR capacity.

    Zip code is 92107, we just bought the house in October and haven't used the furnace, so no good data there unfortunately.

    The challenge is that I need something in place for a home appraisal to finance further renovations, but don't want to drop a bunch of money in the original equipment that will need to be replaced as part of the new construction.

    Thanks for all the good information guys!

    -Mark

  12. #12
    General Engineering Contractor ballvalve's Avatar
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    At 92107 that rig might last 50 years. Thats not Fairbanks. He must have an AC coil on top, which is really about most of what gets used.

  13. #13
    In the trades Dana's Avatar
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    Quote Originally Posted by ballvalve View Post
    At 92107 that rig might last 50 years. Thats not Fairbanks. He must have an AC coil on top, which is really about most of what gets used.
    There are more HDD than CDD in 92107 (about 1000 HDD to 900 CDD), but peak heating & cooling loads are ridiculously low even for fairly non-insulated houses. I wouldn't count on a higher cooling duty-cycle than heating duty cycle.

    At 64KBTU out it could heat my central MA home at design condition twice over. Something tinier would be more comfortable. A ductless mini-split and some air sealing/insulating may be the "right" thing do to, since it would both heat & cool at high efficiency.

  14. #14
    DIY Junior Member sdmarkus's Avatar
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    Hope everyone had a great holiday weekend. Thank you for all the great information and advice. I'm sure I'll have more questions as I begin to research options moving forward.

    Just need to figure out if I can tear this thing out before our appraisal without shooting myself in the foot

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