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Renovating Attic A/C Setup : Switch to Multizone Mini Split, Condition Attic, or Move to Basement?

JRizzo Member Posts: 6
I own a tri level home (quad if you count the basement) with two split A/C units and a boiler. The air handlers are in the attics, which are not conditioned (just lay down insulation). The home is roughly 2,400sqft of conditioned space with a 1,600 square foot floor plan.

The A/C units are very old - 25 to 30 years. I cannot find documentation on them online and they were installed poorly. The primary drain pans are rusting out and the cabinet is corroding as well. I installed an emergency drain pan just to get us through this summer until I can replace the units in spring. However, we are now also dealing with a brown recluse infestations. I have discovered that some are in the ducting, and also likely in the attic. I plan to pull all my insultation and treat the entire attic space. I need assurance of complete coverage, as we have a new born coming in November, but the problem is our attics are no ideal for treating regularly.

I'm planning to kill two birds with one stone here. Update my A/C setup and the attic so it’s easier for me to spray for pests quarterly. I am considering 3 options:

1) Delete the 2 split A/C units and install a multi-zone mini split system. This is my preferred method as it does not require reworking my insulation. However, I am concerned with longevity, ease of service and capability for my large home.

2) Replicate my current A/C setup, replacing the lay down insulation with rafter insulation. I’ve read there is efficiency loss with HVAC in the attic if it is not a conditioned space. How severe is this loss? Worth the cost of re-insulating?

3) Delete the 2 split A/C units, install a single, larger unit in the basement, and run ducting into Attic 1 and across to attic 2. I’m concerned with air flow loss by the time it reaches the upper level – not to mention the converted garage. See (crudely drawn) attached photos for the current setup and proposed #3 setup.

FWIW my father got licensed so he could service and install A/C units on all his properties. So I have someone to assist me who has installed, repaired and refilled several systems. He can purchase freon as well and has most of the equipment we need.