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Thread: mini split heat/cool system

  1. #1
    DIY Senior Member DIY's Avatar
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    Default mini split heat/cool system

    Hi looking for some all across the board info. on a mini split system from HVAC contractors,subs or customers that have this system? prices to expect,best system out there, how many sq.ft. does a single indoor unit cover,. I mean are they as great as these ads and sites make them out to be? etc,

    I want to cool and heat 585 sq.ft. 2 bdrm. 1 bath. ,so all rooms are rather difficult to get equal heat or cool air too with the layout plan with one big window unit or several. Plus efficiency factors with a split like a central system would be great too. Some ads I have seen say these split systems are perfect for an addition of 500 to 1,000 sq.ft. ,or a supplimental heat and air source to your current central system should you find more heat and cool air is desired.'

    Thanks!

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    Plumber jimbo's Avatar
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    585 square feet is an ideal candidate for a split mini system. First, it eliminates need to install ductwork, which may or may not be a big deal depending on access. If you are in a climate where a heat pump will suffice for heating, a heat pump system will work well. You cannot adequately heat and/or cool two rooms with any kind of wall or window system, due to lack of air circulation.

    With the mini split, you would of course choose a flex multizone unit, with an air handler in each of the bedrooms, and one in the living/dining/kitchen area.

    If you are in a cold climate ( below 30) then you need better heat, and will need to consider a full size system , with electric heat air handler or gas furnace.

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    DIY Member Lightwave's Avatar
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    Quote Originally Posted by DIY View Post
    I want to cool and heat 585 sq.ft. 2 bdrm. 1 bath. ,so all rooms are rather difficult to get equal heat or cool air too with the layout plan with one big window unit or several.
    A multi-zone minisplit should be able to handle that provided you're not in a very cold (<17F/-8C) climate. You'll need one indoor unit per major room and a mini ducted unit for the bathroom, hallways and other minor areas.

    Mitsubishi and Daikin are the major manufacturers of suitable minitsplit systems:

    http://mehvac.com/Products/subCatego...CategoryID=153
    http://www.daikinac.com/residential/...oducts&page=54


    What climate are you in?

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    DIY Member Lightwave's Avatar
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    Quote Originally Posted by jimbo View Post
    If you are in a cold climate ( below 30) then you need better heat, and will need to consider a full size system , with electric heat air handler or gas furnace.
    Modern mini splits aren't going to blink at 30F. Mitsubishi's dual head MXZ-2B20NA produces 12,500 BTU at 17F and will generate heat down to 10F. Their top end single room units (e.g. MSZ-FE09NA) produce full rated heating capacity down to 5F and operate at 60% capacity at -13F.

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    DIY Senior Member DIY's Avatar
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    North central Florida here. Last winter was unusually cold for this area in which early and late evenings for a good 3-4 weeks got into the low to mid 20's, and about 1- 2 of those weeks some nights dropped into the teens. Yep, a definate record low for this area! Lightwave does the mini ducted unit run off of a dedicated refrigerant line back to the condensor outside,or "tap" off one of the main air handler lines? 1 of the 2 bedrooms is 11'x12' ~ 12'x12' the other is more like a study room size 9'x10' ~ 10'x10' What i am getting at is do they make smaller air handlers for that size of an area to hang on the wall,or would this mini ducted unit you talk of be better for either room?

    Many thanks to all for the replys!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    The split systems I've read about need two refrigerant lines for each outlet. Effectively, the unit in the room is the evaporator and fan; the compressor(s) is(are) outside. One company sells them precharged, and you don't need to evacuate the system when installing them (just make sure you don't put a nail through one!).
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIY Member Lightwave's Avatar
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    Quote Originally Posted by DIY View Post
    North central Florida here. Last winter was unusually cold for this area in which early and late evenings for a good 3-4 weeks got into the low to mid 20's, and about 1- 2 of those weeks some nights dropped into the teens.
    I've done a fair bit of research into mini splits for that kind of winter environment because it's pretty similar to the winter climate I get here. There is equipment on the market that will deal with weather of this sort but you need to make careful design choices and/or have a very good contractor.

    Lightwave does the mini ducted unit run off of a dedicated refrigerant line back to the condensor outside,or "tap" off one of the main air handler lines?
    Every indoor unit on a multi head mini split has dedicated refrigerant lines and power wiring connected to the outdoor unit. Both ductless (wall hung) and mini ducted units are connected the same way.

    1 of the 2 bedrooms is 11'x12' ~ 12'x12' the other is more like a study room size 9'x10' ~ 10'x10' What i am getting at is do they make smaller air handlers for that size of an area to hang on the wall,or would this mini ducted unit you talk of be better for either room?
    Either a ductless or ducted indoor unit should be able to serve both rooms. Which you pick is just a matter of personal preference whether you want an equipment box hanging off the wall or just a vent in the wall or ceiling.

    The biggest technical advantage to mini ducted units is that they can serve multiple rooms and are, therefore, well suited to handling bathrooms, hallways, and other spaces that are not appropriate for wall mounted units. For example, if you want to heat/cool two bathrooms and a hallway, you can't put a ductless unit in each room but you can use a mini ducted unit to heat/cool all three spaces through a small duct system.

    What you should do next is get your hands on some load calculation software, such as RHVAC or HVAC-Calc, and determine your heat loss and heat gain figures for every room you want to heat and cool. Post the figures here and I'll walk you through the process of designing a system that will work for your needs.

    Have a look at the Daikin and Mitsubishi catalogs when you have a chance, as well:

    http://www.daikinac.com/residential/...-%20Daikin.pdf

    http://mehvac.com/UploadedFiles/Reso...im_catalog.pdf

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    DIY Senior Member chefwong's Avatar
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    I'm planning to do a MrSlim Or Fujitsu as well this year. 2 units - 5 zones.

    The line that runs back to each room, is it insulated or just a *raw* line.

    I know it's going to be a b!atch regardless in these old plaster walls of mine as I will want them inside, rather than being run alongside the exterior and or interior via surface molding.
    Just wondering how large the overall diameter will be for each run.

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    DIY Member Lightwave's Avatar
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    Quote Originally Posted by chefwong View Post
    The line that runs back to each room, is it insulated or just a *raw* line.
    Each indoor unit requires two independently insulated refrigerant lines and one 14-3 power/control cable connected to the outdoor unit. Refigerant line size depends on indoor unit capacity and varies from 3/8" to 5/8". Indoor units also require 15mm (19/32") condensate lines connected to a drain or discharging outdoors.

    Mitsubishi has the Mr Slim installation manuals online:
    http://mehvac.com/UploadedFiles/Reso...02_4-20-09.pdf
    http://mehvac.com/UploadedFiles/Reso...SH_1-28-10.pdf

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    DIY Senior Member chefwong's Avatar
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    Lightwave, I presume/assume you are a HVAC contractor.

    Thoughts in Mr.Slim, vs Fujitsu, Daikin, Sanyo, etc

    I have 3 pending quote visits.

    Shop A says Fujitsu is better the Mr.Slim
    Shop B says Mr. Slim is like *mercedes* and Fujitsu is a Honda
    Shop C is pushing Daikin. They rep Fujitsu and Mitsubishi as well, and rate both as more expensive, less reliable and cost more solutions.

  11. #11
    DIY Junior Member SarahandRoy's Avatar
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    Question Mitsubishi SlimJim molding

    [QUOTE=jimbo;255611]585 square feet is an ideal candidate for a split mini system. First, it eliminates need to install ductwork, which may or may not be a big deal depending on access. If you are in a climate where a heat pump will suffice for heating, a heat pump system will work well. You cannot adequately heat and/or cool two rooms with any kind of wall or window system, due to lack of air circulation.

    Jimbo, it looks like you are online. I hope so. We have a rather complex (at least the HVAC guys think so) system set up. We have one room detached from the main house and it has a Mitsubishi Slim Jim mini-split, cooling that one room only. The mini split has been producing mold and sometimes is actually dripping condensate onto the little "vane" at the bottom that directs the air. Would you be able to communicate with me about this problem?

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    DIY Junior Member SarahandRoy's Avatar
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    Jimbo,

    I am new here and just tried to reply with quote to this thread. I'm not sure what I'm doing, so sorry for any duplication. We have a Mitsubishi mini-split that cools only one small room in our house. That room is unhooked from the main HVAC. We are having mold issues in our mini-split. HVAC people seem confused as to why. The level on the unit (to be sure it's draining properly) and the drain lines have been checked and "all is well." Our SlimJim unit is sometimes condensating so much that water is actually dripping onto the vane that directs the air out of the unit. Any ideas?

  13. #13
    Retired prof. engr. gator37's Avatar
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    Maybe a dumb question but do you have a P-trap on the drain, is your evaporator coil and filter clean?

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    Retired Defense Industry Engineer jadnashua's Avatar
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    There's a drain pan underneath the evaporator coil whose drain hole or hose is plugged up. It needs to be cleaned so the condensate can drain properly. As air is drawn over the (cold) evaporator coil, it condenses the moisture. This falls down into a pan, then normally flows outside via a drain line. If that gets plugged or broken, or rusted out, it can leak.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  15. #15
    DIY Junior Member SarahandRoy's Avatar
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    Hi guys,

    Thanks for your replies regarding our Mitsubishi split system. The filter and coils are clean. The drain line has been checked (just a week and a half ago) and we have been told it's clear. Maybe it could be partially clogged?? It's draining - we can see the water going down the line, but a lot of moisture is still being generated and put into the air.

    When my husband and I had the SlimJim put in (2006), we depended on the HVAC company to properly size it for us, according to our needs. A couple of days ago, we got out a brochure we had, telling how to size your unit to the room. According to our room measurements (13X13), the unit they put in is way too big. I wondered if that could have any bearing on things. I called Mitsubishi and asked them about it - generically, not telling them our specific issues, but pretending to be a new customer. They told me that the recommendations are general and that our HVAC contractor would take into account our specific situation, including how much sun hits that area of the house, etc. I asked them, "What if we get a unit that's much bigger than what is required, just to make sure we have enough cooling? Will that be detrimental in any way?" Of course, they said "no."

    One thing my husband and I remember from when we were first discussing this with the HVAC folks in 2006 is that they said "we don't want to make rain in there" -- referring to the room the SlimJim was going in. No one seems to remember that now but there was some question at the time as to what unit would work for us. After they discussed it amongst themselves, we trusted their judgement and went with what they said.

    Any more thoughts? Thanks a bunch for answering. I am trying to learn my way around here, and how to use this site, so bear with me.

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