Results 1 to 5 of 5
  1. #1
    Join Date
    Mar 2007
    Posts
    1
    Post Likes

    HVAC replacement options...

    Hello all--

    I live near Washington DC, and I'm looking to replace my current (read: OLD) HVAC system. I've done some searching around the forum and have a couple of general advice questions...

    (1) I've had several estimates done, ranging from large shops to one-man operations. The most overwhelming issue is that all the large companies are recommending the 90% efficiency furnace, while the smaller operations seem to be quoting based on an 80% version. Given that I don't plan to be in the house more than 5-6 years (likely less), does the 90% version make any sense?

    (2) My current furnace is vented through my masonry chimney with my water heater. Some companies have said that the 90% furnace needs to be vented out of the side of the house, and one has gone so far as saying that the water heater would need to be re-vented as well so its not orphaned in the chimney. Sub-questions... (a) should/can the 80% efficiency furnace be vented through the side of the house as well, and (b) is the need to re-vent the water heater valid, and (c) again thinking of the less than 6 year timeline, should I really worry about any chimney issues if i go the 80% route? The house is pretty old (1949), and I have no idea about any previous work on the chimney lining though I doubt any has been done.

    (3) My current HVAC setup was put in prior to an addition be put on the house. Again, a staple of the large-company estimate vs. small-company estimate is that the large companies have all said that the current setup is not rated for the space that it is trying to heat/cool, and so they are recommending larger models. I can't complain about the temperature in the house now, so I guess the real benefit of this upgrade would be in the monthly bills? Anyone have any thoughts?

    I'm pretty inexperienced here, so let me know if I left off any important details. Thanks very much for your help, and great work on making such an informative site.

  2. #2
    Join Date
    Sep 2006
    Location
    Henderson, NC
    Posts
    104
    Post Likes
    If you are fine with a 80 percent furnace than do so. It is simply less efficient than a 90 percent (obviously). You can vent the 80 percent furnace out the side but you would have to have a power venter installed (a fan system that would pull the flue gases out) If the company did a load calc and determined that the current system is too small because of the addition than chances are they are right. The current system may heat the house okay but may not cool it properly. Your biggest concern should be to have it done by a professional and have it done right.

  3. #3
    Join Date
    May 2000
    Location
    Indianapolis, IN, USA
    Posts
    40,747
    Post Likes
    Staying 5-6 years, you are at the point where you could get your investment back on a 90 over 80. Plus the advantage of saying you have a very efficient furnace when go to sell.

    Yes, the 90 is side vented with PVC and a metal liner dropped down the chimney for the orphaned water heater alone in an oversized chimney. If you go with an 80, a slightly larger liner would be needed for the 80 and WH to vent in too. You should always follow code even if you won't be there long. Damage could occur in the time you are there. Also a home inspector or building inspector could flag the improper installation and require a correction. Chimney damage is expensive to fix.

    A GOOD dealer will run a heat gain/loss calc and tell you what size equipment you need with the addition in the picture. Of course, GOOD dealers are hard to find.

  4. #4
    Join Date
    Aug 2005
    Location
    Evansville, IN
    Posts
    9
    Post Likes
    Quote Originally Posted by jdaniel View Post
    Hello all--

    I live near Washington DC, and I'm looking to replace my current (read: OLD) HVAC system. I've done some searching around the forum and have a couple of general advice questions...

    (1) I've had several estimates done, ranging from large shops to one-man operations. The most overwhelming issue is that all the large companies are recommending the 90% efficiency furnace, while the smaller operations seem to be quoting based on an 80% version. Given that I don't plan to be in the house more than 5-6 years (likely less), does the 90% version make any sense?

    (2) My current furnace is vented through my masonry chimney with my water heater. Some companies have said that the 90% furnace needs to be vented out of the side of the house, and one has gone so far as saying that the water heater would need to be re-vented as well so its not orphaned in the chimney. Sub-questions... (a) should/can the 80% efficiency furnace be vented through the side of the house as well, and (b) is the need to re-vent the water heater valid, and (c) again thinking of the less than 6 year timeline, should I really worry about any chimney issues if i go the 80% route? The house is pretty old (1949), and I have no idea about any previous work on the chimney lining though I doubt any has been done.

    (3) My current HVAC setup was put in prior to an addition be put on the house. Again, a staple of the large-company estimate vs. small-company estimate is that the large companies have all said that the current setup is not rated for the space that it is trying to heat/cool, and so they are recommending larger models. I can't complain about the temperature in the house now, so I guess the real benefit of this upgrade would be in the monthly bills? Anyone have any thoughts?

    I'm pretty inexperienced here, so let me know if I left off any important details. Thanks very much for your help, and great work on making such an informative site.
    Hope this helps.
    If you put in an 90% furnace you should have a liner put in your chimney that the water heater is connected to.
    If you put in a 80% furnace your chimney should have a liner installed.
    The only difference between the two installation above will be the size of the liner.
    If you have the 90+% AFUE furnace installed:
    You might be able to leave the water heater vented into the chimney without any problems, it depends on the size of the chimney. ( length, diameter)
    Have any of the companies done a load study?

  5. #5
    Join Date
    Mar 2007
    Posts
    12
    Post Likes
    All they do to "re-vent" your HWT is add a chimney liner, its no big deal its done all the time. I also think that a 90+ would be better for a prospective home buyer down the road. A few more dollars spent may bring a quicker sale later.

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •  
Contracting Business
HPAC Engineering
EC&M
CONTRACTOR