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  1. #1
    Join Date
    Jun 2005
    Location
    GA
    Posts
    30

    Gotchas for replacing old systems

    You guys are still the most informative site around, so this homeowner says THANKS for being here!

    My family has had good fortunes (and good maintenance) keeping our systems running for over 20 years. So now is the time to make plans for what if, and I'm trying to see if I have the correct assumptions. In the first, basement setup we have (2) nat gas furnances (4" and 5") and one water heater (3") exhausting into the same (6") B-vent. This vent is in the center of the house and goes straight up, through the 2nd floor and out of the roof where you see the metal vent/cap. From all appearances it is completely double walled, but only a few feet in the basement is visible.

    Since this is in the center of the house, and the basement is finished, it would be highly destructive to try and install any basement level exhaust. So, my assumption is that it would be a good idea to replace these units (I think they are 60k / 80k) with equivalent sized 80% AFUE units? This way I could just reuse the existing vent.

    Likewise for the A/C, we are finally forced to convert from R22 to R410. The linesets have been leak free for years, so my assumption is that they could be flushed and reused? Although they do have rusty looking liquid line drirers outside. Totally replacing them would require tearing out 15-20 feet of drywall.

    Any comments or thoughts would be appreciated.
    1. Replace furnace with a MAX 80% AFUE
    2. Reuse linesets when replacing A/C

  2. #2
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,740
    The driers will be need to be replaced , you can reuse the line set if it is the correct size although I would like it replaced if possible . In Ga a 80 percent furnace is ok . You could look in to heat pumps also

  3. #3
    Join Date
    Jun 2005
    Location
    Winston-Salem NC
    Posts
    1,133
    Efficiency will suffer with an 80%, instead of a 90+, but you have to calculate the costs of upping efficiency versus costs of operation plus costs of fixing everything.

    Line set can be reused, but there is a great deal of controversy over it, with some saying nay and some saying yea. But the issue is are they the correct size for new equipment? If they are not, a new line set will have to be ran.

  4. #4
    Join Date
    Jan 2009
    Location
    Keokuk, IA
    Posts
    5,520
    Without the 30% tax credits, you'll likely never see a payback from the increase equipment and mainly installation cost of a condensing 90+ furnace. Depending on electrical and gas prices, you might look at a heat pump or even better a dual fuel set-up. You might look at a heat pump or dual fuel donstairs and just furnace and stright AC upstairs. The rational, is that the upstairs unit will do most of it's heating at night (since it's where your bedrooms are) and the downstairs unit does most of it's heating in the daytime when it's warmer... and a heat pump will see more use, expecially in the afternoon.

  5. #5
    Join Date
    Jun 2009
    Location
    Albuquerque NM
    Posts
    2,485
    In GA I would go for a dual-fuel set up.

  6. #6
    Join Date
    Feb 2010
    Location
    Ontario Canada
    Posts
    1,341
    I am not too sure about the rules in the US, but here in Ontario, Canada, we are not allowed to put two power vented furnaces into one b-vent. 80% is power vented. I would check into this before making any decisions.
    Never give up; Never surrender!

  7. #7
    Join Date
    Jun 2001
    Location
    Moore, Oklahoma, United States
    Posts
    4,385
    Quote Originally Posted by motoguy128 View Post
    Without the 30% tax credits, you'll likely never see a payback from the increase equipment and mainly installation cost of a condensing 90+ furnace. Depending on electrical and gas prices, you might look at a heat pump or even better a dual fuel set-up. You might look at a heat pump or dual fuel donstairs and just furnace and stright AC upstairs. The rational, is that the upstairs unit will do most of it's heating at night (since it's where your bedrooms are) and the downstairs unit does most of it's heating in the daytime when it's warmer... and a heat pump will see more use, expecially in the afternoon.
    Around here heat pump upstairs and furnace/a/c downstairs seems to be popular. The logic is heat rises and the heat isn't needed much upstairs. Some even use straight A/C w/heat strips upstairs and gas furnace + A/C downstairs.

  8. #8
    Join Date
    Jun 2005
    Location
    GA
    Posts
    30
    Thanks for all the comments.

    Good to hear I was right about reusing the linesets, I'll just have to make sure the system can use the existing sizes. I would have the driers replaced just for looks if nothing else. I had a heat pump before moving here, and will reevalute that option, but there is nothing like the feeling of gas HEAT when you come home to a cold house.

    Agreed motoguy, every calculation I've done so far says that getting a 90%+ Eff furnace would not see breakeven in the foreseeable future. My biggest problem still would be how to run PVC piping without tearing up the entire house. The only wall within reach goes to the garage, but I don't think I can exhaust there.

    trouble time has me worried now, if a 80% is indeed power vented I would have 2 power vented, and 1 naturally vented, going into the single B-vent. Unless someone on here knows the US / GA code, I'll have to ask during my next service call.

  9. #9
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,367
    Quote Originally Posted by trouble time View Post
    I am not too sure about the rules in the US, but here in Ontario, Canada, we are not allowed to put two power vented furnaces into one b-vent. 80% is power vented. I would check into this before making any decisions.
    An 80% furnace is not power vented. They are negative draft furnaces. B vent is not approved for positive pressure venting, which is what you would have with a power vent.

    NFGC permits a 80% induced draft furnace and a nat draft furnace to be vented in the same B vent pipe.
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