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Community and Q&A

Help make my HVAC great in Minnesota renovation

wood0619 | Posted in Energy Efficiency and Durability on

The quick rundown is that I am renovating my 1970 rambler basement. I have added R-13 to the basement walls and R-10 on the floor. In the end, the wall assembly will be close to R-30 and spray foamed rim joists once I insulate the wall cavity.

A room-by-room manual J I have performed indicates I have 8k BTU load in the basement with 30k BTU load upstairs (I have attached this report, the first 2 rooms on the room list are the only ones in the basement). At this point, I am looking to update the HVAC ductwork and plan to go to a fully modulating furnace. The smallest modulating furnace I have found it 60k BTU which will scale down to 40% capacity. In order for both floors to be nice and comfortable do I need to zone upstairs and downstairs? Any other ideas from the energy nerds? (this is a huge compliment btw)

Additionally, Does anyone recommend a great HVAC company in the Minnesota MSP area?

I should note that I am also planning to do a tankless water heater and a drain water heat recovery unit on my main stack.

Thank you for any advice and feedback.

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  1. Expert Member
    Dana Dorsett | | #1

    >"In order for both floors to be nice and comfortable do I need to zone upstairs and downstairs?"


    The heat load of a mostly-below-grade basement varies only modestly with daily outdoor temperature swings, but varies quite a bit seasonally with the temperature of the soil. There's no good way to run it on the same zone as upstairs and get consistent indoor air temps. In summer there can even be a slight heat load in the basement when there's a cooling load up stairs, and the basement's cooling loads are almost 100% latent load.

    Running a hydronic baseboard loop or tiny dedicated hydro-air coils off the water heater makes the most sense for zoning the basement. It's not hard to find thin profile hydronic coils that will deliver the appropriate amount of heat at domestic hot water temps, eg: (there are others)

    Most local codes will allow "open" systems using potable water in hydro-air solutions as long as the total plumbing lengths are limited. (The limit varies by jurisdiction or state.) Worst-case potable compatible plate type heat exchanger can be used (even for fin-tube baseboard).

    When using a tankless for space heating be sure to spec enough heat emitter to not short-cycle the tankless-it's the same math as with modulating condensing boilers:

    BadgerBoilerMN is a pretty good contractor in the MSP area, but primarily for hydronic systems. The founder/owner Morgan Audetat may be semi or fully retired at this point, but he's one of the few HVAC contractors whose Manual-J numbers I would trust.

    A 40K-50K-in 2-stage hot air furnace for the upstairs, or an appropriately sized modulating hydro-air handler running off the tankless can handle the upstairs loads comfortably enough.

    It's possible to get about 29KBTU/hr out of a 3-ton FirstCo 36HBXB-HW with 120F entering water temp, 40K at a 140F entering water temp, and both the water temp and blower speeds can be modulated with a bit of design:

    1. wood0619 | | #2

      I will try and reach out to badger boiler. I investigated this hydronic air handler combination from Rheem, and it does look promising. One Rheem contractor I contacted said they would not install that. I don't get why it’s hard to find HVAC contractors doing these integrated type systems.

      My primary plan at this point is to do a modulating communicating furnace with damper actuated supplies for upstairs and downstairs. One thing about hydronic in my case is I still need ventilation year-round and AC, which means I still must properly duct the basement and hydronic becomes nice to have redundant.

      1. Expert Member
        Dana Dorsett | | #4

        >"One thing about hydronic in my case is I still need ventilation year-round and AC, which means I still must properly duct the basement and hydronic becomes nice to have redundant."

        Ventilation air flows are miniscule compared to heating & cooling air flows, and ventilation is still needed even when there is no heating or cooling load. Also, a room's ventilation needs are not proportional to it's heating or cooling loads. Using the heating/cooling ducts for ventilation isn't ideal.

        BTW: The FirstCo air handlers all come with cooling coil options. There's a bit of a trade off on oversize factors with most houses. Per your Manual-J you have less than 2 tons of combined latent + sensible cooling load, and a peak whole-house heating load nearly 2x the cooling load. Backing off to the 2.5 tonner in that previously mentioned series, the FirstCo 30HBXB-HW R410 TXV could still get you there with 135-140F without a crazy oversize factor on the cooling. The Rheem RW1*04A 2-tonner might be a better fit, delivering ~37K at an EWT of 140F.

        BTW: If you haven't already figured it out Badger is in Eden Prairie :

        1. wood0619 | | #6

          I have made contact with Badger Radiant and plan to have them do an assessment for me. They are running 30+ days backlogged and it is unclear how active their business still, but I am going to give it a shot.

          Regarding the HRV that is a whole separate topic, it sounds like. Can you point me to the best methods to duct these? I currently have a Honeywell Truefresh VNT5070H ducted into my air return. It sounds like it would be best to separate this out into a separate ducted system. Right now I have access to separately ventilate the basement, but not easily the upstairs. I can draw air out of the basement bathroom and closets and potentially 2 basement bedrooms as well and then drop fresh input into the basement living space. Would it be wise to also dump into the return air side for supplying fresh air to upstairs? (I can interlock with the furnace low speed fan and heating/cooling).

  2. DAVID GOODYEAR | | #3

    dettson offers a range of furnaces from 15kbtu to 100kbtu. They also have their own ducting system with zoning controls.

    1. wood0619 | | #7

      Hi Dave,

      I have not been able to find someone who installs and services this brand in the Minneapolis area? Any suggestions?

  3. user-723121 | | #5

    I use Marsh for HVAC, the best I have found.

    1. wood0619 | | #8

      Marsh is going to provide me with an estimate to zone the system. I was a little worried about some of the rules-of-thumb sizing that the person they sent out was using.

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