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Thread: Sizing Home Mini-Split

  1. #1
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    Sizing Home Mini-Split

    Hello!

    My fiancé and I just bought a house which currently is heated with electric baseboards (no ducts in the house) and want to install mini-split heat pumps.
    We are getting an electrician booked to help us fix some electrical issues as well as wire in the circuits for the HVAC.

    Where I have a bit of concern is in terms of designing our HVAC solution. So far we've contacted two local HVAC companies and neither of them asked more questions than "how many sq.ft." or "how many bedrooms".
    Looking at several posts here, there seem to be quite a few more factors that should come into consideration when determining the size and placement of the units and I am concerned we might not get the optimal solution...

    Our house is a split level with cathedral ceilings in part of the living room, but neither of the companies we talked to seemed to consider that.

    I am not sure if I am overthinking this, but I have a 3d model (my.matterport.com/show/?m=wmtkZ6uKJjv&lang=en) of the house and I was wondering if any of who had insights to help us at least start in the right direction.

    Both companies recommended a 18k BTU unit on main floor and one on the second floor.

    Any insights would be greatly appreciated,
    Thank you very much!

    Vincent

  2. #2
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    I've seen some contractors install 1 larger unit on each floor and that's ok.......... I guess. With that kind of design you're going to expirience uneven heating, and the bedrooms are going to be noticably a lot colder. Ideally you'd install a wall unit in each room, but this is a lot more work and materials. However, that's how I run my own home and it works really well, especially since at night I can shut down the rest of the house and only heat my bedroom while I sleep. Ultimately you'll have to decide how much you're willing to spend on this project......

  3. #3
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    Thread Starter
    Thanks James, that’s definitely a consideration we will keep in mind!

    In terms of the sizing, should I expect the HVAC companies to perform a load calculation or using square footage should be ok to estimate our needs?

    Thanks

  4. #4
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    Quote Originally Posted by Vince22 View Post
    Thanks James, that’s definitely a consideration we will keep in mind!

    In terms of the sizing, should I expect the HVAC companies to perform a load calculation or using square footage should be ok to estimate our needs?

    Thanks
    No unfortunately they wont. Insist that one is done. Expect to pay for this service up front.

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  6. #5
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    Looking at that 3D images this could get expensive.

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  8. #6
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  10. #7
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    I dont know what your goal is here but if your trying to heat and cool the entire house it'll need 6 zones. This house is pretty common for me in my area. Ive done many hundreds like this. But its very tricky if you haven't done them before.

    Bottom floor would get a 9k Hyperheat....Bottom floor is always the coldest. 9k is the smallest Mitsubishi makes in low ambient units.

    Main floor would get an 18k Hyperheat....Not even worried about the size on this unit I would want the air throw so I could insure I can get a good volume of air into kitchen. It really should go on the wall that's looking into your front yard. It needs to throw air across the living room and toward the kitchen. This area is tricky because we its running slow in heating the air will want to rise since you have a small vault right in front of where the wall mount would be. But I see you have a ceiling fan there and it will help wonders to run it on low speed in the winter when that main floor is heating.

    3rd floor. Well your house is designed as 4 floors. Well call it Piano room. This room is tricky as well. If you don't use it it can be left alone. if you do use it you ll need a zone there for cooling. But the problem is that area is wide open to the main floor so while its not that big it might need a unit much bigger than it would normally have since its open to the main floor SQFT and its higher so that heat will rise. Nice thing is the room is small so you can at least get away with air throw. But I would likely put a 12k in that room.

    4th floor. you'll need three 6k zones in there. one for each bedroom. the computer room you have to pop into the bedroom closet and out the side of the house since there is no wall space.

    Depending on weather where you live will determine if the upstairs and piano room need low ambient units or not.

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  12. #8
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    Quote Originally Posted by Vince22 View Post
    Hello!

    My fiancé and I just bought a house which currently is heated with electric baseboards
    (no ducts in the house)
    and want to install mini-split heat pumps.

    We are getting an electrician booked to help us fix some electrical issues
    as well as wire in the circuits for the HVAC.

    Where I have a bit of concern is in terms of designing our HVAC solution.
    So far we've contacted two local HVAC companies and
    neither of them asked more questions than
    "how many sq.ft." or "how many bedrooms".

    Looking at several posts here, there seem to be quite a few more factors that should come into consideration when determining the size and placement of the units and I am concerned we might not get the optimal solution...

    Our house is a split level with cathedral ceilings in part of the living room,
    but neither of the companies we talked to seemed to consider that.

    I am not sure if I am overthinking this,
    but I have a 3d model
    (my.matterport.com/show/?m=wmtkZ6uKJjv&lang=en)
    of the house and I was wondering
    if any of who had insights to help us at least start in the right direction.

    Both companies recommended a 18k BTU unit on main floor and one on the second floor.

    Any insights would be greatly appreciated,
    Thank you very much!

    Vincent
    Cut & Paste of
    my.matterport.com/show/?m=wmtkZ6uKJjv&lang=en
    to browser did nothing for me
    regarding YOUR specific model.

    ZIP code _ _ _ _ _
    Age of residence

    Foot Print
    Wall Heights

    Window Schedule
    _________ U-factor 0. _ _ S.H.G.C. 0._ _

    Infiltration : ~ 0.35 ACH Natural
    Designer Dan __ It's Not Rocket Science, But It is SCIENCE with Some Art. _ _ KEEP IT SIMPLE & SINCERE ___ __ www.mysimplifiedhvac.com ___ __ Define the Building Envelope & Perform a Detailed Load Calc: It's ALL About Windows & Make-up Air Requirements. Know Your Equipment Capabilities

  13. Likes Vince22 liked this post.
  14. #9
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    Thanks Jacob!
    Our main goal is to cool in the summer as well as gain heating efficiency in the winter. We are ok to continue using baseboards to supplement some of the heating needs.
    I really appreciate your insight, the companies we talked to seemed to place the two 18k units quite differently (see attached). On the main floor (2nd picture in Red) it was pushing air widthwise rather than lengthwise as you've proposed and on the 3rd floor it was on the landing between all the rooms (1st picture), there are high closets all the way to outside wall.


    Quote Originally Posted by jacob-k View Post
    I dont know what your goal is here but if your trying to heat and cool the entire house it'll need 6 zones. This house is pretty common for me in my area. Ive done many hundreds like this. But its very tricky if you haven't done them before.

    Bottom floor would get a 9k Hyperheat....Bottom floor is always the coldest. 9k is the smallest Mitsubishi makes in low ambient units.
    We might wait for a second step for the basement, as this will likely get more expensive than we initially thought

    Main floor would get an 18k Hyperheat....Not even worried about the size on this unit I would want the air throw so I could insure I can get a good volume of air into kitchen. It really should go on the wall that's looking into your front yard. It needs to throw air across the living room and toward the kitchen. This area is tricky because we its running slow in heating the air will want to rise since you have a small vault right in front of where the wall mount would be. But I see you have a ceiling fan there and it will help wonders to run it on low speed in the winter when that main floor is heating.
    I have 3 questions for this one :
    1. I assume that for the one above the front yard windows (2nd picture in orange) they will need to run the lines up to the attic and then back down the side of the house. How long can the run be before losing too much efficiency?
    2. Eventually we wanted to remove the stone arch above the sliding doors (2nd picture in green), would placing the unit there be a good option? (more direct lines to the side of the house it seems to me)
    3. Would placing the Unit widthwise as suggested by our local contractor (2nd picture in red) or towards the back of the house aimed at the kitchen (2nd picture in blue) be a problem?


    3rd floor. Well your house is designed as 4 floors. Well call it Piano room. This room is tricky as well. If you don't use it it can be left alone. if you do use it you ll need a zone there for cooling. But the problem is that area is wide open to the main floor so while its not that big it might need a unit much bigger than it would normally have since its open to the main floor SQFT and its higher so that heat will rise. Nice thing is the room is small so you can at least get away with air throw. But I would likely put a 12k in that room.
    We will use it as a home office for the time being... We will plan for a unit in there. Could that unit help alleviate some of the inconvenience of option #3 above by pushing hot/cold air in the front area of the living room (combination of 2nd picture purple and blue)?

    4th floor. you'll need three 6k zones in there. one for each bedroom. the computer room you have to pop into the bedroom closet and out the side of the house since there is no wall space.
    Not sure that we have the budget yet for 3 more units... If we keep the doors open would it be sufficient to have one unit on the landing between the rooms (1st picture)? Are there ducted systems that could go in the attic and push conditioned air to the 3 rooms? The ducting runs would be quite short

    Depending on weather where you live will determine if the upstairs and piano room need low ambient units or not.
    Attached Images Attached Images   

  15. #10
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    Hi dan,

    Thanks for your reply, here are some more information

    Quote Originally Posted by dan sw fl View Post
    Cut & Paste of
    my.matterport.com/show/?m=wmtkZ6uKJjv&lang=en
    to browser did nothing for me
    I had to remove the h t t p s:// to post, maybe adding it back would make it work
    regarding YOUR specific model.

    ZIP code _ _ _ _ _ The house in Montréal, Quebec, Canada
    Age of residence 33

    Foot Print Approx 2000sq ft without the basement
    Wall Heights Most of it has 8' ceilings with a portion of the living room and piano room with ceiling of up to 16'

    Window Schedule
    _________ U-factor 0. _ _ S.H.G.C. 0._ _

    Infiltration : ~ 0.35 ACH Natural

  16. #11
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    Quote Originally Posted by Vince22 View Post
    Thanks Jacob!
    Our main goal is to cool in the summer as well as gain heating efficiency in the winter. We are ok to continue using baseboards to supplement some of the heating needs.
    I really appreciate your insight, the companies we talked to seemed to place the two 18k units quite differently (see attached). On the main floor (2nd picture in Red) it was pushing air widthwise rather than lengthwise as you've proposed and on the 3rd floor it was on the landing between all the rooms (1st picture), there are high closets all the way to outside wall.
    Designing these systems isn't to difficult as long as you understand function.

    The unit has somewhere around 750 speeds. Its job is to run as slow as it can while doing what your asking it to do. If you put a unit in an area where supply air can mushroom out and hit a wall, and cycled that air back into itself(What is called short cycling), the unit will just slow way down. The location on the 4th floor in red is a horrible location. Yes it is at the peak of the home where the most heat will accumulate but the air will just recycle into itself and the unit will barely run.

    The purple location. Yes you could put a 18k head there and it would do a decent job of cooling the main floor because it is quite open and has decent air throw. But doing this would completely deny its ability to heat the main floor. If cooling is your only concern it would be an OK location.

    Red location on main floor. It will work. but it'll work better with the longer throw. removing the bring would also work but I don't like that location as much either because it is quite offset from the kitchen. So getting air into the kitchen will work but not nearly as good as if you put it where I marked the purple. From that location you can turn the vanes to throw into the living room or kitchen. From the spot where the brick is it wont turn and throw the air into the kitchen. ATLEAST, based on how the pictures look....Primarily, the wife is in the kitchen. We NEED her to be comfortable, our life depends on that....

    The unit in the landing. Ok so it appears that the ceiling height of the landing is also the ceiling height of the 4th floor bedrooms. Which is good. If you mounted that unit 1" off the ceiling on the wall it would do a decent job of removing hot air in the entire house. Your still gonna have trapped air inside the bedrooms because the door opening is 2' off ceiling height. But it'll do quite a lot of work.

    The only location in the hallway that would work somewhat OK I've posted a pic of. Do to the way that hallway is air will certainly recycle back into the unit no matter where it put up there.

    If I were designing this project. On a budget-friendly price, with ONLY cooling in mind, I would use the 24k WR series Mitsubishi mini split in the landing high up on the wall. WR series is a 16 SEER product that I buy 20 at a time. These units are worth the weight in Gold. I use them in cabin lofts and homes with lots of floors like yours. They ramp up quicker and run at higher speeds most of their life since they are taking the brunt of the load in the house.

    DO keep in mind the unit has a filter that must be washed every few months. so the height can be a bare if a ladder is required.

    MUZ-WR24NA-U1
    MSZ-WR24NA-U1

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