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  1. #14
    Join Date
    May 2008
    Location
    Missouri
    Posts
    3,422
    We are near Kansas City and I can count on one hand the number of 100k, 90% gas furnaces we've installed in a residential home in 30 years. You must have a REALLY big house, or you're buying just what you are replacing....trouble. When purchasing a 90% furnace, DON'T oversize it, that way you actually get 90% efficiency and the furnace will last much longer. Has anyone actually done a heat load (manual J) on this house? Is your ductwork sized to deliver 2000 cfm??? I'm betting "no" to both. I feel sorry for you if you actually own a house that loses 90,000 BTU/Hour of heat. Even with this 90% furnace, you going to have a HORRIBLE gas bill!!! If your HVAC guy is sizing the furnace by measuring the doors to the furnace area.......RUN!!!!! If your HVAC guy is sizing furnace by standing in driveway with thumb in air (and squinting)...RUN FASTER!!!!

  2. #15
    Well i hope im not to late . They just finished installing the furnace. The old unit was a 125k btu 90% unit . My house is a older 2 story farm house that has been bult on to . Total sq ft up & down is 3000 . I asked them about the btu and he did tell me no you dont need that big of a furnace and he explained bigger not always better and the whole effeciency deal with a lower btu furnace. Now when we 1st spoke on phone he said 100k btu but i honestly didnt look at that today . I will look and see if i can find out what byu it is. I do know this . We turned furnace on and it ran approx 5 mins and the house was warm immediatly and it didnt run forever like the old unit .

  3. #16
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,139
    [QUOTE=tiger man;1515934 Weve had three sooted furnaces in the last week, all fifteen years and newer[/QUOTE]

    is this uncommon??

    @wahoo..LOL! at holding up fingers to size units. I've had this 'shown' to me several times.
    not a loac calc or sizing by any standard other than bs.

    best of luck OP.
    Last edited by energy_rater_La; 02-07-2013 at 11:40 AM. Reason: punctuation
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  4. #17
    Join Date
    Jul 2010
    Location
    wisconsin
    Posts
    270
    Quote Originally Posted by energy_rater_La View Post
    is this uncommon??

    @wahoo..LOL! at holding up fingers to size units. I've had this 'shown' to me several times.
    not a loac calc or sizing by any standard other than bs.

    best of luck OP.
    No its not uncommon at all on carrier and payne and bryant, on lp, ive condemned over a hundred heat exchanger due to soot in the last three years

  5. #18
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,882
    I totally agree with tiger man; I'd have a Home Energy Efficiency Rater/Audit performed, then do the cost effective work, then have a heat-loss calc performed so you don't way oversize the furnace.

    A 57,000-Btuh Output furnace will heat a good sized well weatherized home even in sub-zero weather; get all the numbers run!

    What climate do you live in; near what major city in your state?

  6. #19
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    790
    Quote Originally Posted by ga-hvac-tech View Post
    Propane is a DIRTY fuel... it needs filtering before entering the furnace (a moisture trap would be a good idea).

    I agree with the others... get the new furnace; be SURE it is converted to LP, and have it serviced annually.
    LPG is dirty? How you figure that?

  7. #20
    Join Date
    May 2004
    Location
    south louisiana
    Posts
    3,139
    x3 on the energy rating. and load calculation.

    rating & sizing is small price to pay for years of comfort/affordability.
    air sealing leaks in both house & duct system is low material cost
    with fast comfort/payback.

    best of luck.
    The cure of the part should not be attempted without the cure of the whole. ~Plato

  8. #21
    Join Date
    Jun 2005
    Location
    SW Wisconsin
    Posts
    4,882
    Propane is a DIRTY fuel... it needs filtering before entering the furnace (a moisture trap would be a good idea).
    On NG & propane, dip-legs are supposed to be installed on the horizontal run area just before where the piping enters the furnace.

    Does your furnace have one?

  9. #22
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    20,893
    Quote Originally Posted by MicahWes View Post
    LPG is dirty? How you figure that?
    NG furnaces need less maintenance... and LP furnaces need more cleaning.

    Also LP has lots more moisture issues.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  10. #23
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    790
    Well, that is true since the hydrocarbon content of LPG is higher and it is more difficult to achieve complete combustion. The fuel itself is not physically dirtier though. Since it boils off from a liquid in the tank as you use it, the gas itself shouldn't need any filtration of any kind. Only pure gas will boil off.

  11. #24
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,140
    NG requires 10 parts air/ one part fuel while LP requires 24:1, butane 31:1

    All fuel gases are blends but LP is historically more contaminated with heavier hydrocarbons such as ethylene, iso-butane, etc. that all require even more air for proper combustion. Now, these heavier fuels are more difficult to mix thoroughly with air so you tend to get a little or a lot of incomplete combustion. That can mean CO, aldehydes, and soot. When you fill an LP container the heavier stuff sinks to the bottom where it can remain for the life of the tank. However, under certain conditions, esp. warmer temps, these fuels may vaporize and mix with the propane resulting in dirty pilots, yellow tipped flames, and possibly a little higher temps. We see this same thing with NG during high demand periods where they spike the gas with other junk called "peak shaving". Its a way to meet demand while using some stuff left lying around so to speak. Actually, everything does get used such as in the petro chemical industry but you try to get HD5 propane, which means it is 95% pure propane and less than 5% ethylene. We have a pipeline from Belvedere, Tx to Eagle, Pa. The same local supplier may buy bulk of the "good stuff" one week then some cheaper, less refined crap the next.

    A sediment trap is required before all gas utilization equipment with a few exceptions like fireplaces and gas lamps. Most guys will call them "dirt legs" or "drip legs" but those are misnomers. The trap must cause a 90degree turn so the gas turns into the appliance combination valve while any solid or liquid impurities will fall by gravity into the trap. Even if a building official doesn't specifically call for it, the code still requires sediment traps installed.

  12. #25
    Join Date
    Sep 2005
    Location
    Atlanta GA area
    Posts
    20,893
    Good explanation Hearth!

    What I find is LP fired furnaces create a lot of soot. Even when I tune one with a CA unit... next year there is more soot. Theoretically that should not happen... unless the quality of the fuel varies... right?

    Also I find gas valves in furnaces burning LP tend to fail sooner than NG gas valves. Break open a failed LP gas valve... you will find dirt and rust... RARELY does one find that in a failed NG valve.

    Talked with a guy years ago... he told me LP tends to have more moisture in it than NG... thus some of the problems.

    There are the obvious things... and there are the other things... IMO one needs to study to know BOTH.
    GA-HVAC-Tech

    Quality work at a fair price with excellent customer service!

    Romans Ch's 5-6-7-8

    2 Chronicles 7:14

  13. #26
    Join Date
    Oct 2009
    Location
    Raleigh, NC
    Posts
    790
    Where do you think rust and dirt come from in an LPG system? Where does all this excess moisture come from? It certainly doesn't boil off in the storage tank with the fuel.

    Sent from my ADR6350 using Tapatalk 2

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