Manual S & Fujitsu Equipment Selection Zone 3A
I’m replacing an absolutely clapped out old 2 ton package heat pump & leaking ducts with a ducted mini split & moving duct work from a vented crawl space to a vented attic. I’ll be adding a little square footage in the future & of course improving insulation & air sealing as I can(plenty of room for improvement). I had about settled on a Fujitsu AOU24RGLX outdoor unit paired with a AMUG24LMAS air handler. The best I could do for a manual S is the one from loadcalc.net & I was surprised to find that the system I’ve selected is not sufficient.
Obviously, I don’t want to oversize the system & latent capacity is a big concern here. Can someone get me pointed in the right direction? I could also use some guidance in understanding how the CFM numbers from my manual J(attached) play in to equipment selection & duct design.
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
I'll respond to give your post a bump.
Pay a professional to perform a manual J. If you didn't have capacity problems with your old equipment, it's evidence your calculations are incorrect. For comparison, your calculated heat load (~31k btuh) is similar to my slightly larger, basically uninsulated triple wythe brick house @ 8°F (~33k btuh).
Consider keeping the ducts where they are and spending the money conditioning your crawlspace.
Professional doesn't seem to mean much around here I'm afraid. The current equipment does struggle on the most extreme days or extended hot or cold spells...it is 37 yrs old & falling apart though. I figured even with the added square footage, new equipment of the same size & ducting with close attention to details would do the job. I would love to condition the crawl space, but it just ain't gonna happen right now. I have other reasons for moving the ducts anyway. Thanks for responding, I will look over my Manual J again.
Do you really have no insulation in your floor?
I do not. Pretty common around here.
You have a few options. I think your uninsulated floor is really driving your heat load.
1) Insulate your floor, etc to reduce your loads to within the 2 ton unit.
2) Hire Energy Vanguard to do your Manual J, S, and D
3) Put in a 3 ton unit
Depending on your floor plan and ceiling heights, I would also consider running short duct runs in a central hallway or in soffits to keep them in the conditioned space.