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HVAC Upgrade/Modification For Increased Comfort

Tim_O | Posted in General Questions on

I’m looking for some advice regarding our HVAC system, or otherwise regarding some improvements we could make.  We are looking to build a house in the next few years, but we will be here in the meantime, and I spend a lot of time here (WFH).  The house in question is a 1960s single story ranch, around 950sqft with a basement.  R11 in the walls (guessing), R49 in the attic.  And the attached garage shares a 24ft wall, and is heated/cooled with a heat pump.  Windows are newer, but low dollar horizontal sliders.  Detroit – climate zone 5.

For equipment, nothing is that old.  I have a 13 SEER 2 ton AC, and an 80% 80,000BTU furnace.    

For load analysis – I used a Borst calculated to estimate around 11,000 BTU total heat loss.  8,000 being sensible and 3,000 being latent.  Using the furnace sizing article on GBA, heat load comes in around 13,000 btu/hr.  This was lower than I calculated with Borst, and lower than I anticipated.  I calculated for a few different periods and got roughly the same result.  

Now that issue I’d like to address in order of importance to me.
1) Summer humidity – even with the indoor temp at 69-70*, humidity is often above 60%.  I’d rather drop humidity and increase the temperature to ~75.  Not surprising with my AC system.  It’s often in the 70s outside with thick enough air you can swim instead of walk if you prefer. 

2) Cold kitchen floor – I often sit at the kitchen table for work all day.  The tile floor here stays pretty cold, 65* or so.  It’s right in front of a (bottom dollar Anderson) sliding glass door (“doorwall” as they say in Michigan).  The air gets a bit cold too when the heat is between cycling.

3) Basement heat distribution – We have a finished basement, and the far end of it has no vents.  There are 3 total vents in the basement, and one poorly placed return.  The far end of the basement gets fairly cold with no air movement.  My thinking is a return here would be a huge benefit. 

So obviously my equipment is way oversized, and that’s probably a big part of it.  When I moved in, I wasn’t that educated in proper design, and just upgraded the attic from R8 to R49 (blown cellulose).  With R8, my equipment might have decent run time…  In the shoulder seasons, like now, it’s cycling on only for a few minutes at a time.  My ductwork is run below the floor joists, so all in the conditioned area.  I cut and cobbled together insulation in the rim joist below the kitchen to try and improve that area.  I didn’t do the whole basement however.   

Now, given all that, I’m not interested in doing a huge tearup here.  Ideas I had that address some or all concerns:
Single minisplit head in the livingroom/kitchen area – keeps air mixing and should help the humidity issue if sized appropriately. 
Standalone dehumidifier – ducted or just in the basement. 
Replace furnace/AC with a ducted heat pump -this seems like it would be more expensive than it’s worth, and we do have good condition equipment as is from ~2016.
Small electric heater of some sort near the sliding door.  I don’t really want a mobile unit, I’d prefer something more permanent and out of a toddler’s curious reach. 

What would the community suggest?  Thanks!

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Replies

  1. user-6623302 | | #1

    Gas or oil furnace? Where is the thermostat? Do you use setbacks or some on/off strategy? How often does the furnace run on a cold day?

    1. Tim_O | | #2

      Natural Gas. Thermostat in the hallway. Setback only at night a couple degrees, otherwise pretty much 70* all day - could just turn it up to 72, but the air temp in the rest of the house away from the door gets a bit too warm.

      The house is 24x40, kitchen/dining/living room combined. A short hallway off that with three bedrooms and a bathroom. Thermostat is 4ft down the hallway from the open area.

      1. user-6623302 | | #4

        How long does the furnace run on a cold day. Do you heat the basement all the time.

        1. Tim_O | | #5

          Basement is heated all the time , but with the minimal supply/return vents, it's 63* when the upstairs is 70.

          I'm not sure how much it runs on a cold day. It hasn't gotten that cold here yet.

  2. Expert Member
    Akos | | #3

    I think the simplest fix in your case is one of the staple up resistance matts. Easy to install if the basement is open and provides the heat exactly where you want it. As long as you only raise the temperature of the floor a bit above room temperature, the running costs would not be that much. Make sure to insulate underneath with batts and to air seal the floor joist bays where the matt is installed as big air leaks can overpower them.

    As for humidity, around me a stand alone dehumidifier in the basement is the norm, not too expensive to run and cheap to install.

    1. Tim_O | | #6

      I like that. It's easy to access, below the kitchen is the utility room with open floor joists. Only issue would be that the tiles are installed over the old wood floor, so it's a bit thick. I thought that maybe that would overwhelm the heat matt too.

      1. Expert Member
        Akos | | #7

        Tile is about R0.25, if you have an inch of drypack under it, say R0.1. One inch subfloor adds about another R1.2 or so. In total you are looking at ~R1.5, which is not much at all. As long as the batts bellow are above R10, most of the heat will to flow to the room above.

        About the only issue I've had with tile over drypack is that sometimes the drypack can be very thick if the subfloor was very crooked. This is a fair bit of mass and it might take 2 to 3 hours for the floor to come up to temperature. I would program the thermostat to run the floor heat on a couple of hours before needed, this way it is warm when you walk downstairs.

        Once you lived with heated ceramic tile, you won't be able to go back to cold floors again.

        1. Tim_O | | #8

          Sounds good! I'll look into doing this.

          1. Tim_O | | #13

            I ended up going this route. Finished up the install yesterday. Just two joist bays in front of the glass door, also where I sit for work. It works quite well and was easy to install!

          2. Expert Member
            Akos | | #17

            Glad to hear it worked out. A bit of floor heat in areas like this can make a huge difference in comfort.

  3. walta100 | | #9

    Tell us about how well sealed is this house. Has it been blower door tested?

    If it is fairly well sealed, I would open up or add registers in the basement.

    Note if your numbers of 70° up and 63° downstairs are real measurements and not guesses based in your gut feeling, it seems almost impossible to get that big a temperature differential across an uninsulated floor that is leaking lots of air between the two spaces short of a open basement windows.

    I don’t see a problem with running a dehumidifier to mask the problem of the oversized AC unit set at 60% or so.

    Walta

    1. Tim_O | | #11

      It has not been blower door tested. But based on my gas usage from last year, it seems tighter than I would have guessed.

      70* and 63* are real measurements. But that 63* is 20ft from the nearest register and my slab and walls of the basement are not insulated as far as I know. About 2 feet of exposed concrete above ground level. But also a window well near that 63* point, with no insulation on all that exposed concrete as well. With no air movement on that half of the basement, I'm not too surprised it gets to 63*.

      Now with all that said, that's the opposite side of the house from the cold kitchen floor. The kitchen floor is over the only room in the basement without a drop ceiling and with both a supply and return vent. That room stays close to 70* pretty much.

  4. Expert Member
    PETER G ENGLE PE | | #10

    If the basement air is really about 63F, that could be a big part of your comfort issue. Just insulating the floor could make a big difference. Insulation plus staple up mats will be like heaven.

    1. Tim_O | | #12

      See my above post on the details, but the 63* part of the basement is on the opposite end of the house as the cold floor I sit at. Still not ideal though!

  5. walta100 | | #14

    To drop the temp of the basement 7° there is a huge energy leak somewhere nearby like the size of an open window! The smart move is to fix the leak

    Walta

    1. Tim_O | | #18

      I'm thinking an uninsulated wall/slab is it. Along with dead air and a window well.

  6. user-6623302 | | #15

    Have you checked the duct to make sure everything is connected and there a no closed off sections?

  7. andyfrog | | #16

    I don't really think this is a realistic option given your preferences, but maybe keep in the back of your mind the CERV2 (~$8,500) - it would integrate pretty easily with your existing ducting and systems, and provide a smaller 1/3 ton system that could provide supplemental heating, cooling, and dehumidification when your existing systems won't run.

    For dehumidification purposes, any kind of remote method is probably nicer to live with than any portable dehumidifier. Those tend to be pretty noisy. That said, they are surprisingly powerful if you have an open floor plan. We have one sitting in a bathtub in a bathroom at the end of the home and it is surprisingly decent at managing humidity in a greater range than I would have expected.

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