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Questions about minisplits and Manual J

Ryan O'Rourke | Posted in General Questions on

Is it possible for someone to provide me with a a manual J online without visiting my home? I cannot find anyone in my area who I feel is qualified.

I can provide whatever info is needed. I’ve drawn details sketches of all measurements of my home. I’ve had a blower door test. I know the insulation levels.

We are planning on making improvements over time, however. But I’m interested in a current calculation based on what I have right now. And then as I make improvements I can see how it will adjust the load requirement.

Besides this, I’ve been evaluating mini split systems for some time now. Many of my rooms are small and going to have small load requirements. I noticed recently the MSZ-FH06NA. Is this a new unit? It’s very inexpensive. One issue last year was that the MSZ-FH09NA was the smallest head unit and was oversized for some of my rooms. I know it’s not necessarily ideal to have a head unit in each room, however.

I’m open to the SEZ cassette in certain locations, however, it seems fraught with other issues. What I don’t quite understand is how does this unit work? If it just installs into one ceiling, then why does it need a duct at all? What does the duct connect to if it’s just serving a single room?

My understanding is that this can also serve 2-3 rooms which could bring the overload load requirement closer to the unit capacity. In this case, which room would I install the unit in? Is there any benefit to the room the unit is installed in vs the units connected via ductwork? I’d rather use an FH06NA in these small rooms however due to efficiency and low temp heating capability if it indeed modulates at a much lower BTU/h than the 09NA, though. But the only specs I can find on it suggest that the minimums are the same?

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Replies

  1. Ryan O'Rourke | | #1

    I found another thread on here about the FH06 which answered most of my questions about that unit. I see it for very cheap online which still makes me think it would be good for some rooms.

  2. User avatar GBA Editor
    Martin Holladay | | #2

    Ryan,
    Another thread (Mitsubishi minisplits — horizontally ducted) discusses your issue.

    GBA reader Ismail Mohammed considered two companies to do his Manual J calculation: Energy Vanguard (Allison Bailes) and Home Energy Partners / HVAC Design Pros (Isaac Savage). He ended up going with Home Energy Partners, which is located in Asheville, North Carolina.

  3. Clay Whitenack | | #3

    Ryan, another (free) option would be to attempt the Manual J yourself. CoolCalc.com is a free online manual J software. I found it to be very good for a free program. You can run room to room calculations or just whole-floor calculations. There is a learning curve, and sometimes it can be a little buggy, but if you have the patience to sit down and enter in the inputs, it will give you a fairly accurate answer.

    I used the software for the house I am building and was able to to learn enough about the process that I can spot errors in the calculations. This came in handy when some local companies ran their calculations and came back way off (higher) than what I had calculated.

  4. Tim Brown | | #4

    There has been a dire need for a Manual J calculator for a LONG TIME that is easy both to use and FREE.
    I have been struggling for months (stretching into years), to get a Manual J that I could rely on for a couple of projects. Like Clay related above CoolCalc has an online calculator that is relatively easy to use...took a few tries but I ended up with numbers I believe... and as in his experience the calculations are about 50%-60% of the HVAC pros WAG (Wild A-- Guess) I have been receiving. No one locally will do a Manual J without a commitment that they will get the HVAC work.
    I encourage others to try it!

  5. Ryan O'Rourke | | #5

    Thanks for the suggestions. I'm most interested in learning how to do it myself, but it's hard to find a lot of resources for learning how. I've downloaded and installed BeOpt, and started playing around with it, but I could not draw the shape of my house. They don't seem to offer options for cape cod style houses. I'll check out CoolCalc as it seems simpler, just hope that I can come up with something that's indeed accurate.

  6. Clay Whitenack | | #6

    Ryan,

    I tried BeOpt as well, but found it fairly limited at giving me the detail I was looking for. Coolcalc has some "how to" videos on Youtube that may help. https://www.youtube.com/channel/UC6c4tEhUWN6Yy6odPFrfIrg

    My best advice to you is to not get frustrated. Lay in there and take the time to figure it out. It will take a while to enter in all the rooms, but you can save your progress and come back to it later. Think about the reward you will receive when you get an accurate result, which will probably be an equipment expense that is probably half of what you would have paid otherwise. Worth the time, in my opinion.

    Having said all that, I decided to hire a pro to do a manual J to double-check my numbers. I figured it was a small price to pay to feel more confident about the large difference between my numbers and the local HVAC folks. I haven't gotten my results back yet, but when I do I'll report back here to let you guys know how close the software got.

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