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What if pro wants to use existing size hvac?

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Comments

  • ratio
    ratio Member Posts: 3,616
    I was looking for a meme that expressed my response to that. I failed to find one.
  • EBEBRATT-Ed
    EBEBRATT-Ed Member Posts: 15,455
    Agree with @ratio , ductwork is ALWAYS undersized. WHY?

    One reason is to save $$$

    The other reason is if they size the ductwork to the heat loss.

    Let's say your heat loss is 60,000 and the furnace is going to be oil fired.

    So you put in 60k worth of duct and the smallest oil furnace is 80k of output now you have too much air flow for the installed duct
  • ChrisJ
    ChrisJ Member Posts: 15,592
    > @EBEBRATT-Ed said:
    > Agree with @ratio , ductwork is ALWAYS undersized. WHY?
    >
    > One reason is to save $$$
    >
    > The other reason is if they size the ductwork to the heat loss.
    >
    > Let's say your heat loss is 60,000 and the furnace is going to be oil fired.
    >
    > So you put in 60k worth of duct and the smallest oil furnace is 80k of output now you have too much air flow for the installed duct

    I sized the ductwork for my AC based on 0.05" drop if memory serves. It was difficult to get a lot of it to fit. I did 9" drops to bedrooms.

    And even after using stuff that everyone told me was way too big, with the largest Merv 8 airbear they make on a 3 ton I still end up with 0.5" total static half the time. It starts around 0.4 and I change the filter when the total gets near 0.6.

    I have no idea what static most systems are running especially with 1" thick filters and undersized ductwork.
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • SlamDunk
    SlamDunk Member Posts: 1,571
    I'm going to switch topics since I started this tread a year ago. Because of covid ( you know, was only going to be a short term thing), we essentially locked down and haven't reached out for quotes yet. I was going to make my first trip next week and get a quote or two.

    I saw on the news recently that there is a shortage of units and long lead times. The reporter said this is causing the price of installation ( and repairs) to be higher than normal... Is this true? Or false?

  • pecmsg
    pecmsg Member Posts: 4,776
    Unfortunately TRUE
    SlamDunk
  • SlamDunk
    SlamDunk Member Posts: 1,571
    Darn!

  • GW
    GW Member Posts: 4,691
    I’ve seen oversized duct work. It happens 
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • pecmsg
    pecmsg Member Posts: 4,776
    GW said:

    I’ve seen oversized duct work. It happens 

    1 out of how many?
  • GW
    GW Member Posts: 4,691
    100 
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
    pecmsg
  • PC7060
    PC7060 Member Posts: 1,155
    edited June 2021
    ratio said:
    Protip: the ductwork is always undersized. :sunglasses:
    I recently replaced a four ton carrier AC with a 1-1/2 ton unit with transitions to the original 14”x24” main duct that split through a tee into two 12x18 lines servicing the two sections of the first floor.  I had a local HVAC company run the new lines and set up the unit and they did great job.   

    Unfortunately the sales guy came along and spent his time trying to convince me to replace my “oversized” duct work.  I politely declined. 

    Fan noise is almost inaudible and balancing the dampers in the original ductwork is a breeze. ;)

    bucksnort
  • GW
    GW Member Posts: 4,691
    Wow PC that’s quite a drop. Excellent. Is the air blowing well in all the registers? I’d think it would be hard to fill the bag. That’s some bigger ducting. 14/24 is yuge 
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • PC7060
    PC7060 Member Posts: 1,155
    edited June 2021
    Yes, @GW, those are monster duct but the system works well with pretty even air distribution. The envelope of the house was tightened significantly as part of a renovation so BTU requirement match up nicely with small HVAC.   The HVAC runs long periods and is effective at both cooling and pulling humidity out of the environment. 
    Old 4 ton unit would run for 15 minutes and dump temperature down quickly but the short cycle times left a lot of humidity. 
    The 3 ton unit on second level was replaced with a 2 ton two stage High velocity system with all new ductwork. Again good air sealing (home and ducts) were critical part of the project.  
    GW
  • SlamDunk
    SlamDunk Member Posts: 1,571
    pecmsg said:

    Unfortunately TRUE

    Got my first quote. Wow. On to the second quote......I may have to, and can, wait until things settle down or my system dies and forces my hand.
    bucksnort
  • pecmsg
    pecmsg Member Posts: 4,776
    SlamDunk said:

    pecmsg said:

    Unfortunately TRUE

    Got my first quote. Wow. On to the second quote......I may have to, and can, wait until things settle down or my system dies and forces my hand.
    Shortage of equipment is one thing, shortage of qualified techs is a bigger issue. To retain quality the contractor has to pay more which means YOU have to pay more!
    Don't expect the pricing to come down any time soon.
    Waiting until its dead and having to rush the job is never a good idea!
    Panic buying leads to poor quality.
  • SlamDunk
    SlamDunk Member Posts: 1,571
    The price quoted warrants additional quotes for comparison. It is always a good idea to get more than one quote. I learn something new with each visit.
  • ChrisJ
    ChrisJ Member Posts: 15,592
    Are there shortages across the board, or are higher seer systems still plentiful?

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • SlamDunk
    SlamDunk Member Posts: 1,571
    I decided to go with a high efficiency nat. Gas furnace when I do this replacement. I have a question about the combustion air intake. Does it have to be piped outside if I have foundation vents? It seems if intake temps are stable, combustion will be stable.
  • ChrisJ
    ChrisJ Member Posts: 15,592
    If it was mine I'd be pulling from outside.

    The less you pull through your foundation the better.

    That's my opinion.

    My dad's furnace frosts up the intake PVC when it's -20 outside.  Seems to burn plenty happy though.

    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • JUGHNE
    JUGHNE Member Posts: 11,042
    You say "foundation vents"....is this a basement or crawlspace?

    Where is this located?

    Here in NE, we treat either as a conditioned space with some duct runs into the areas.
  • ChrisJ
    ChrisJ Member Posts: 15,592
    JUGHNE said:
    You say "foundation vents"....is this a basement or crawlspace? Where is this located? Here in NE, we treat either as a conditioned space with some duct runs into the areas.


    I've been trying to condition all of mine the best I can as well.  No vents, sealing up leaks etc
    Single pipe quasi-vapor system. Typical operating pressure 0.14 - 0.43 oz. EcoSteam ES-20 Advanced Control for Residential Steam boilers. Rectorseal Steamaster water treatment
  • SlamDunk
    SlamDunk Member Posts: 1,571
    edited June 2021
    It is a full basement with a partial crawl space thirty ft away. Three or four vents over there. Plus windows are steel frame tilt ins. Old wood door 15ft from furnace. Not an air tight basement at all. In NC.
  • JUGHNE
    JUGHNE Member Posts: 11,042
    Does the ductwork extend into the partial crawlspace?
  • SlamDunk
    SlamDunk Member Posts: 1,571
    Yes, actually, to the registers.