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  1. #1

    Red face Mini Split in Columbus Ohio


    We are just finishing an addition on our home (or rather, our contractor is).
    We had already decided (based on our contractor's advice) to have a mini split (cooling and heating) installed for the addition (single room open to the rest of the house - about 17' x 20' with ceiling heights of 8' and 11' and 3 exterior walls facing west, east and sheltered south - pretty well insulated with energy efficient windows).
    However, the install cost seems a bit high (our contractor was going to sub this out to an HVAC guy), so I want to do some independent research before I proceed with this guy - quote is $4,000 installed.

    I have a few questions. We are thinking of the 12,000 btu Mitsubishi mini split - heat and cooling single unit.

    1. How does it handle the really cold temperatures? Although Ohio tends to stay above 20 degrees F in winter, we do usually get a cold snap for about a week or two in winter - below zero. The sub mentioned something about making sure we have emergency back up heat for those times. Is this the auxilliary heat that kicks in on these units or is this an additional heat pump? In other words, if you buy any of the mitsubishi units, do they all have this emergency back up heat? Is it really expensive to operate when this kicks in?

    2. Not sure what kind of circuit this needs. We have limited capacity on our 100 amp service. Does it need a 20 amp circuit or more?

    3. We are getting additional quotes from "regular" HVAC contractors, but so far, they seem a bit unfamiliar with this. One person said we would have to upgrade our electrical service because the unit would require close to 50 amps. All the specs I am reading show 20 amp. What should we look for when picking a contractor to install this system. Are they that unusual?

    4. What are the operating costs for something like this compared to hooking it into our gas forced air/heat pump system? I am kicking myself for not investigating that option before starting the remodel. Our air conditioning unit (heat pump?) is pretty old and probably is very inefficient, so we may have killed 2 birds with one stone. I am unsure if our furnace could have handled the additional load. So we may have faced upgrading our air and furnace and running ducts, but would the total system have been more efficient to operate in the long run? Or is it better to zone the addition with a mini split.

    Any feedback would be appreciated.


  2. #2
    Join Date
    Jan 2002
    I have installed no less than 30 Mitsubishi " mr. slim" units this year so far and nearly all have been for addition/sun rooms. Typically, a 20 amp circuit feeds the outdoor unit. A four wire tray cable or similar wire connects from the outdoor unit to feed power to the indoor unit. So, a double pole 20 amp circuit is all that is needed. Always have a professional determine electrical capacity existing in your panel. Just because a "slot" is available does not mean a circuit can be added!

    Ductless systems seem to be a good option for the simple reason that general contractors often do not know the correct way to calculate the increased load of the new space. Most times they will just tap into the existing supply duct. Even more rarely will they even consider return requirements.

  3. #3
    Join Date
    Mar 2004
    I had a 12,000 BTU Mr. Slim heat pump installed in my 16x18' sunroom just this summer. I looked into trying to use existing heating and cooling system...but just too hard and expensive to do.

    The Mr. Slim did an excellent job cooling my room all summer...I rarely had it lower than 78 to keep things comfortable. As for winter, my Mit. dealer said it would handle our cold weather here in PA. Just the other morning it was 30 and the heat pump warmed the room quickly. On bitter cold days, you may need to use an electric heater...depending on how comfortable you are with cold weather. I have an extra oil-filled space heater to use if needed, but I think the Mr. Slim will do fine.

    My unit was installed for about 500 under your quote.

  4. #4


    Thanks for the information.

    I have had a couple of other contractors in this week. I neglected to mentioned that the sub thought a 2 ton unit would be needed. That seems like overkill to me, especially since the addition is open to the rest of the house and will benefit from heat or cooling from the adjoining room.

    We think a 1 ton unit will be adequate as did both of the HVAC contractors we had in this week.

    One HVAC person also recommended as an alternative, to install a hotel room unit. We would have to run a 220 line to it, but the unit itself is only $1200 and requires a framed opening to the outside. He thought our contractor could install it for us. I am not familiar with these units.
    Anyone have experience with those...or would most people agree that the Mitsubishi unit is the way to go?
    The reason he recommended the hotel unit is that we will probably have to upgrade our entire system in about 5 years, so he suggested it may make sense at that point, to tie in the addition to the entire gas forced air system.

    Any thoughts?

  5. #5
    Join Date
    Jul 2004
    You're getting the normal responses to your question. As many people as you ask, you'll probably get as many ideas back. First and foremost, DEMAND to see the heating/cooling loads calculated using Manual 'J' so you don't throw your money away. A space that needs 1-ton of cooling in the summer could very well need 2-tons for heating in the winter. Why? Because the heat pump will only deliver about 50% of its rated capacity at low temperatures. So if you don't want to rely on some other form of heat, you'll need that capacity. Don't skrimp, you'll regret it. The Mr. Slim by Mitsubishi puts the owner in the nest of the largest producer of mini-slits in the world. While others may sell for less, when it comes to technical back-up and support, there is none that compare with Mitsu. I say this from professional experience. With the Inverter technology, a 2-ton Mr. Slim can go down to approximately 9,000 Btu's and therefore easily handle both the heating and cooling needs of the room.

    You're building this room so you can enjoy the comfort of it. This is NOT the time to start seeing how cheaply you can get it done. If the Mitsubishi dealer is a Diamond Dealer, you KNOW he's been properly trained to size and service the Mr. Slim. That's great insuarance and as we all know, insurance costs money. So...........
    If YOU want change, YOU have to first change.

    If you are waiting for the 'other guy' to change first, just remember, you're the 'other guy's' other guy. To continue to expect real change when you keep acting the same way as always, is folly. Won't happen. Real change will only happen when a majority of the people change the way they vote!

  6. #6
    Join Date
    Feb 2003

    The Hotel AC units

    Are PTAC's. They're available as Heat pump or just AC with electric strip backup.
    Cheaper yes, but more noise. They're still wall unit AC's GE Zoneline has some nice models. HP's that has electric backup also.

  7. #7

    Mitsubishi it is

    Good points.

    Sounds like the Mitsubishi is the way to go.
    No one showed me any load calculations, so you are does the contractor know what size unit is right for that space.

    I have no objection to spending money..I just want to make sure I am making the wisest investment.

    I will look for an installer who has a relationship with Mitsubishi.

    thanks again!

  8. #8
    Join Date
    Mar 2004

    Go to the Mitsubishi website and you can find a list of local dealers/installers. I must say that I had two Diamond dealers out to my was waste of time...did not want to do a Man. J...he just knew what the room wanted...he was shown the door. The other Diamond Dealer was great...came out and took measurements and looked over my room. Then came back a few days later and went over the calculations with me. Spent a lot of time answering my questions and made me feel very comfortable. He and his installers were always on time and were very polite to my family. They have also contacted me a couple of time since the installation to see how things were going and if I had any questions or issues...that's service in my opinion.

    I looked into the PTAC thoughts of saving some $$ (hoped to use the extra $$ to get plasma TV). In the end...they were not worth the savings...did not want to see a unit coming out of the wall...on either the inside or outside. I know they make better quality units than the one's I have run into at motels...but just not worth it when I wanted to use the room full time.

    Make sure you get the heat and cooling load calculations completed so that you get what you need. I don't think you can go wrong with Mitsubishi.

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