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  1. #1
    Join Date
    Mar 2019
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    Whole house forced air or mini-split?

    Hello Iím currently looking to get a new system installed in to my home. House is in San Diego built in late 50ís, around 1300 sqft, 3bed/2bath. Outdoor climate is fairly mild all year but the extreme ends of the spectrum would be 30-110 degrees. Currently the house has a natural gas wall furnace located in the kitchen. We went in to this thinking we wanted a central forced air heat/ac system but are now also considering mini-split.

    Weíve had three contractors come out for proposals. All of them have shared the same two issues with installing the forced air system. 1.)The only place to install the new furnace is the hall closet right outside all the bedrooms and they are warning it will be loud. 2.)The bigger issue is a room addition (built in the 80ís I think) that has a flat roof so ducting in to it isnít simple.

    The room addition is about 300 sqft attached to the dining room and kitchen which together are another 500sqft. Itís completely open for about a 20ft span between these areas other than a beam that sticks down from the ceiling about 16 inches. One contractor wants to run a duct on top of the flat roof for this room. The other two say theyíd just put too large vents right on the attic side of the beam but Iím worried how well this will work with no air flow in to the addition area.

    So then one of them worked up a proposal for a mini-split system instead. It would be a 48K BTU outdoor unit, 3 9k ceiling cassettes for the bedrooms, 1 18k ceiling cassette for the dining and kitchen area and a 9k wall mount for the addition. Itís a Mitsubishi system and would cost about 25% more than the forced air proposals.


    Looking for some unbiased feedback on thisÖ
    1.) With the forced air system, will the noise really be an issue so close to the bedrooms?

    2.) With the forced air system, will the addition be properly heated/cooled with the two large vents near, but not actually in, that space? (Iím not thrilled about the roof penetration idea, should i reconsider?)

    3.) With the mini-split, how will the cost of running it as a heat pump compare to natural gas? (In my mind ďrunning the ACĒ for heat sounds expensive)

    4.) What is the expected life-span of the mini-split equipment? (They said Mitsubishi is a 15 year warranty)


    Is there any other factors we should be considering? What would you recommend?

    Thanks!

  2. #2
    Join Date
    Mar 2010
    Location
    Houston
    Posts
    204
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    You are asking some great questions, but itís very hard to give you definitive answers with so many unknowns such as where your home is located, and the overall tightness and energy efficiency of your home. i.e., good windows and doors, lotís of shade trees, and stuff like that.

    Also, not sure how the condition of your existing HVAC system. It sounds like youíre on gas heating now.

    My first thought was what about a hybrid, where you add a mini-split to the new addition and call it a day.

    Mitsubishi miniís are terrific. They are legit if installed properly. The heat pumps (I personally own 5) are very efficient in the right climates. They are intended to stay on all the time and they adjust to load requirements constantly rather than starting and stopping. They are extremely quiet. They are reliable and there are more and more qualified dealers out there to service them.

    Not sure how to answer the noisy air handler in the closet question. Perhaps you can go into an attic or two by visiting some friendís place and have a listen to the running unit. I will say better air handlers are quieter overall but that is very subjective. RVs and mfg homes put air handlers in closets as do many apartment complexes. I guess you get used to the hum?

    I cannot address the elec heat pump vs nat gas question. My guess is the natural gas is probably cheapest unless the miniís are in a nice tight building envelope. The Miniís energy consumption is very low for me where my ducted system was terribly lossy and inefficient. Like you, I didnít have space to put good proper ductwork in my place so the mini split decision was a no brainer for me.

    I have implemented many of the Mitsubishi units over 11 years, nearly all of them heat pumps. Every single customer has been thrilled with them. Most said the added cost was recouped in energy savings in <5 years and they loved the ability to give room by room climate control too.

    Iím sure some others will chime in with their take and help you make a good decision. You definitely have some good options regardless.

  3. #3
    Join Date
    Nov 2006
    Location
    Athens, Ohio
    Posts
    6,543
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    Consider doing both.

    Our kitchen/DR addition is above a crawlspace which is 7" high and inaccessible. I installed a Mitsubishi Hyper Heat unit which has kept the room at 72į even when it is below 0į outside.
    The main house has a dual fuel system (gas furnace and heat pump). In your case, make sure that the duct system is big enough and it won't be noisy. I recommend having at least 8' of return trunk to isolate blower noise. Be sure they use Manual J for calculating the load and Manual D to design the duct system.
    AOP Rules: Rules For Equipment Owners.

    Free online load calculator: http://www.loadcalc.net/


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    It's = contraction of it is. Its = the possessive form of it
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    Questions should end with a question mark "?" Statements end with a period "."

  4. #4
    Join Date
    Mar 2019
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    2
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    Thread Starter
    Quote Originally Posted by KeyResults View Post
    You are asking some great questions, but itís very hard to give you definitive answers with so many unknowns such as where your home is located, and the overall tightness and energy efficiency of your home. i.e., good windows and doors, lotís of shade trees, and stuff like that.

    Also, not sure how the condition of your existing HVAC system. It sounds like youíre on gas heating now.
    House is in southern California, about 4 miles inland from the coast. Windows and doors were all replaced with reasonable quality double-pane about 5 years ago. None of the exterior walls have any insulation and there's a very minimal covering (barley to the top of the 2x4 joists) of rockwool in the attic. No shade at all.

    The only source of heat is the wall furnace which will be removed. There's no current ducting anywhere.

    Quote Originally Posted by kdean1 View Post
    I recommend having at least 8' of return trunk to isolate blower noise.
    They would be putting the furnace on top of a pedestal with the return directly underneath. So this must be why they are warning about the noise.



    Thank you both for your advise. I think i'm sold on the mini-split as long as i can confirm it won't be overly expensive to heat with vs natural gas. Having a really hard time finding any info to make this comparison especially since the current furnace doesn't provide any useful point of reference.

    But given that an average "cold" day here is around 55 it doesn't sound like the mini would be working very hard at all.

  5. #5
    Join Date
    Feb 2006
    Location
    Float'N Vally, MS
    Posts
    2,760
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    We get a little colder here and I am doing a whole house ductless this week.
    You get heat pump economy with zoning all in one...
    Just gotta get bast the inside look.
    Life is too short, Behappy!
    TFMM

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