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  1. #1

    Question after renovation: larger ducts or shunts?

    We recently raised the roof of the family room , creating a 2 story great room with a wall of windows.HVAC is an older 2 stage heat pump. It is a vacation home, not used as much in the winter. The family room has a wood burning fireplace.

    Just heard from the builder:
    "I met with our contractor yesterday. We talked about the new volume incurred with the addition. A heat load study was performed and we offer the following for your consideration.

    * The existing system is 3-ton
    * The load calculations on the entire home including modifications would require a 4-ton system
    * Our contractor suggested as a starting measure to increase the air to the living room by enlarging the existing floor vents and boots from 2x12 to 4x12 in three locations. Then go through a winter and see how things feel. Other options to then consider would be adding electric baseboard heat or upgrade heating system. Since the glass wall is facing north, cooling may not be an issue. To enlarge the floor vents would cost $ XXX.00."

    Is paying for larger ductwork and floor vents a better option than adding shunt valves in the ducts leading to other rooms? Is it more sensible to add portable electric heaters until we bite the bullet and replace the 20 year old heat pump. (maybe go geothermal, or propane backup heat pump)?Other ideas or comments? Thanks

  2. #2
    Also.. which is preferred way to increase heat volume--- adding new registers, or enlarging existing registers and boots. If enlarge existing registers and boots, do they need to increase the size of the feeding ducts?

  3. #3
    Join Date
    Nov 2008
    Location
    Chapel Hill, NC
    Posts
    1,070
    If the ducts are accessible and reasonably easily replaced, I would do that (you may also need dampers in all of the supply ducts to properly balance the air distribution). See how that works and then upgrade the H/P and air handler if needed. If the ducts are inaccessible, then I guess you could enlarge the boots and registers only, but I don't know that will accomplish a whole heck of a lot.

  4. #4
    Join Date
    Jul 2001
    Posts
    3,112
    What is a shunt valve?

  5. #5
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,712
    Ask them to measure the air flow (in CFM) that the unit is currently moving.

    Many duct systems aren't moving enough air to get the units full capacity.
    So increasing the size of the existing supplies in that room, and may be ading or increasing our return size.
    May be all you need to do for cooling.

    As for heat.

    Might want to just keep using the fireplace for now.
    And then zone that room when you hange out the system at a later date.
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  6. #6
    thanks for the replies. The renovation contract specs called for "adding registers as needed". Am thinking enlarging the existing registers and boots is their "construction alternative". I'm fine with that--if it works. Don't need more unsightly floor registers.

    can they just add a second return vent adjacent to the existing return-- doubling the return square footage?

  7. #7
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    67,712
    Depends.

    I can't see if its possible from here.

    If the room is there for the duct and grille, yes.
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