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Thread: HVAC question for basement remodel

  1. #1
    Experienced handy man PATNJ's Avatar
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    Jun 2005
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    Post HVAC question for basement remodel

    I'm putting a rec room in the basement and have an HVAC question regarding the placement of the registers and cold air returns, and the number of each I should install.

    The room is 17x12. There will be 2" XPS insulation on the exterior walls with
    2x4 framing and 1/2" sheetrock. I'm going to install 3 1/2" pink panther noise insulation in the ceiling and in the wall near the laundry and heater. The concrete floor will have a HDPE mat with plywood, probably covered with carpet.

    Where is the best place to put the registers and returns? The easiest would be to put both in the ceiling, but I'm concerned that both installed on the same level will not create sufficient air flow. I've come across the recommendation that for a basement you should reverse the "normal" locations such that the returns are low and the registers are high, to help remove the cold air normally present at floor level.

    Questions:
    1. How many registers and returns?
    2. Where to put them?
    3. Should I insulate the existing duct work that will be in the ceiling, or will the noise insulation be sufficient?
    4. What size ducts for the basement?

    I'm looking for experienced advice. Thanks.

  2. #2
    In the Trades brownizs's Avatar
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    First question, is the furnace even sized to handle the load for allowing the basement to be heated? Ours was sized to allow for expansion if we decided to finish our attic space into a living space, which means that we have to keep it at 66 to keep from getting heated out of the house.

  3. #3
    Retired Defense Industry Engineer jadnashua's Avatar
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    The more ideal situation would be to add in-floor radiant heat in a basement. The floor will conduct heat to the colder earth. I'd want to introduce heat down low so it isn't pooled at the ceiling. Running the fan continously can help prevent stratification. One thing that works well is to install a longer supply run with two outlets in the wall - one near the ceiling and another near the floor and only open one, depending on the season. In the winter, open th ebottom one so hot air comes out there, then floats up. In the summer, open th eupper one, so the cold air comes out there, and floats down. In either case, you can remove the hot air from the ceiling, and if the fan is running all of the time, recondition it and run it around.

    Most of the expertise here seems to be plumbing rather than HVAC, but one that knows one branch of the trade has some experience with the other...and, I'm not a pro, either.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  4. #4
    Renovator Gencon's Avatar
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    Furnace size should not be an issue as it is sized for an uninsulated basement and should only become better after the reno.Ideally, registers should be located in the ceiling, in front of windows. A proper heat load calculation will tell you how much hot air is required to heat the room and thus the size of the duct and registers.There are a few of these calcs available for free online.
    If there are existing registers in this area already,thier size and number will be fine, but looking at your numbers, I would guess at 2 6" runs with 4x10 registers.
    A single low wall return is required for finished basements in most jurisdictions and should be around 1.5 times the size of the supplies for the area its serving.
    Sealing all the ductwork with foil tape is a very beneficial step in getting the air where you want it. Most residential duct systems can leak as much as 25-40% of the air through gaps in the ducts.
    Insulating with a foil backed duct wrap will ensure the heat gets where it needs to be as well as the air flow.
    Since you will be building a subfloor with carpetting, the floor will be much warmer.

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