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Optimizing my ductwork to combat low airflow

giantseangiantsean Posts: 61Member
Hi All,

I've shared many a tale of woe from an ~2500 sf old mostly-masonry house renovation including a new central hydro heat/air system. I won't go rehash every detail but you can see most of the original issues here -> https://forum.heatinghelp.com/discussion/157442/more-winter-more-problems#latest

Since then I've done a few useful and important things:

- Fixed all the backwards plumbing
- Had an energy audit and done a lot of my own air sealing as well (audit blower door test indicated ~1000cfm improvement), fixed duct leaks where I could find them
- Replaced the incorrect heat pump zone controller w/ a Honeywell HZ432, installed DATS in one supply trunk
- Rigged a relay w/ timer to address air handler blowing cold air during a DHW call
- Bought an Ecobee w/ multiple sensors to help balance the rooms

The above (and probably some things I haven't listed) have made a pretty significant difference. The house definitely stays warmer and holds temp much better. Not perfect, but at least now it's livable. The last big job I have is to try to optimize the 1st floor ductwork, and that raises some new questions

Right now I have a 2 zone 1st floor due to the (at the time) huge variation in temps on different sides of the house (due to differences in insulation, which have more or less been fixed now). My 1F air handler (AS AAM7) is set up "wrong" ie it is set for max fan for an external (non-slide in) hydro coil. This is to allow sufficient CFM to hit the 2nd zone while both zones are calling for heat. No matter what, It is given that I have to seal the ductwork better (it was not sealed by installers) and replace flex with metal duct. That said, I am not sure that will fully solve the problem of enough pressure across the system. Now that I have the DATS installed, I can also see that temps spike quite a bit from the usual 105 to higher when the fan blows more slowly. So I have a few ideas:

- Set the fan to the proper speed and Install a booster for zone 2 DOWNSTREAM of the coil to help the air get to the end of the house
- Now that there is less difference between zone 1 and 2, scrap the 2nd zone completely and lose the remainder of the zone 1 trunk, run the branches into the zone 2 trunk (keeping the plenum the same
- I have also been told the ducting is wrong as some branches run straight off the end of the trunk (I forgot the term for the extra amount of run that allows pressure to build) so either way that can be fixed.
- Also wondering if I need more returns in general, as they are all located toward one side of the house. I know you aren't supposed to have returns in a kitchen, but I'm wondering if I stick to the "dining" end of the kitchen we can avoid smells
- Speaking of the kitchen, it is probably the coldest area overall. Wondering if some more supplies would also help.

I've attached a duct map to help illustrate. Sorry for writing a huge book but this effort has become somewhat of an obsession for me... I'm going to beat this house into submission one way or the other :P

Thanks for any advice!


Comments

  • Jamie HallJamie Hall Posts: 10,469Member
    You need -- among other things -- to get returns into the zone 1 section of the house. I presume there is a door between the music room and the kitchen? That's too bad... but at least returns in the music room will help.
    Jamie



    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.



    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • giantseangiantsean Posts: 61Member
    edited February 10
    Sorry I realized after I posted that it's not the greatest diagram. It's actually Mud Room (but music room sounds way better lol). The ductwork is all in the basement and the openings in the diagram match the basement vs. the actual 1st floor. The only doors are to the Office room, everything else is open (some in more than a couple of places)

    The basement on the other hand is somewhat limited. The only openings for ducts are pretty much where they are. The Mud Room is actually over a crawlspace and the Living Room is over a 2nd basement, both products of non-original additions - meaning the ductwork goes through what used to be a tramsom window to outside.

    There is probably some room in that opening to pass a round duct through for a return, though it would be a routing nightmare to tie it in the the return trunk once it entered the main basement, due to where everything is situated. I might be able to get it into the plenum itself.

    That said, the Mud Room is newer w/ R21 insulation, and except for the sliding door area stays pretty warm, unless it's very cold and there is some wind wash from the crawlspace (despite the R30 in the floor). Also worth noting that the house is built into the side of a hill and the basement and crawlspace are walk outs.
  • Jamie HallJamie Hall Posts: 10,469Member
    It's not so much to get the mud room -- music room does sound better! -- warmer, it's to get air moving in that side of the house. Forced air systems are very sensitive to returns -- and no return, no hot air...
    Jamie



    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.



    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • giantseangiantsean Posts: 61Member
    I can definitely consider it (routing notwithstanding) but how about one in the kitchen as well (the eating side), like right here... which would be infinitely easier (though still a PITA):

  • Jamie HallJamie Hall Posts: 10,469Member
    That should help a lot -- you'd be surprised.
    Jamie



    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.



    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • giantseangiantsean Posts: 61Member
    Thanks again. Aside from the additional return, is there any advantage to moving to a single zone for the 1st floor? Either way I'd probably need a booster or two to move the air, unfortunately.... unless you think capping the end of those ducts (the "BAD" spots) will solve it. Clearly is it losing velocity once it gets to the other side of the house, but I'm not sure if that's due to pressure issues, leakage issues, too much flex, or just too far away (or all of the above).

    I guess the real question is, with around 800CFM at the AH, and with my particular layout, if everything was perfectly sealed and sized, would that still be too long a trunk to hold pressure and maintain velocity (the farthest register from the AH is ~65-70 feet away), or would I need some other drastic change? (redesign or different equipment)
  • Jamie HallJamie Hall Posts: 10,469Member
    If in fact you are losing velocity, that means you are losing air volume -- which means leaks. Fix them! (It's usually a lot easier for air than water... :) )
    Jamie



    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England.



    Hoffman Equipped System (all original except boiler), Weil-Mclain 580, 2.75 gph Carlin, Vapourstat 0.5 -- 6.0 ounces per square inch
  • giantseangiantsean Posts: 61Member
    Noted, and it's part of the plan. Is there a rule of thumb for how much velocity loss vs distance in a well-tuned system? I have a cheapo anemometer and can take values at the closest and farthest duct to compare.
  • DZoroDZoro Posts: 761Member
    Keep in mind if you want air out, you have to make sure you let it in. 13- 6" supplys @ 19sq in =247 sq in of openings. Both supply and return duct should equal 10"x25" to handle those equal openings. Your return openings need to equal 247 sq in. also.
    Don't shoot me but this is a rough rule of thumb.
    D
  • giantseangiantsean Posts: 61Member
    Assuming I leave the zones alone, I can probably convert the far left kitchen register to a return very easily ( I think code prevents anything much closer) but I supposed I'd need a register to replace it too. Maybe between the windows that don't have it now, or over the zone 1 duct (though it would be in a corner abutting an oven and a fridge) The living room is a lot tougher unless I run additional ductwork. The lone return in there is a 12" (maybe 14") flex through the wall opening to the other side. The mud room may be near impossible unless I convert the farthest one or change the ducts to all round and even then it would be a plumbing nightmare. Also have to consider getting too close to the stove as there is an old window opening connecting them (along w/ a doorway). Maybe I just need to just double the size of my existing returns lol.

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