Please help me pick the best option for HVAC replacement
We moved into this 20 year old house here in Nashville, TN in June and have been doing various projects to bring the home up to and above current building best practices. We have put open cell foam in the attic (average ~8 inches with rafters covered) and have encapsulated and foamed the crawl with 1.5 in of closed cell and 12 mil vapor barrier. We replaced the upstairs HVAC with a new 5 ton Trane xr17 and S9v2 furnace.
With all of those items complete… I am running out of funds for improvements! BUT.. we “have” to replace one of the two existing downstairs HVAC package units because one of them is 20 years old and apparently has a cracked heat exchanger, so I am told I will have no heat at all from that unit this winter. So I have come up with a few options and bids to fix this issue, and want to get input from the community here please.
1) Simply fix / replace the heat exchanger only on this 20 year old package unit. I am advised against this by the local HVAC contractors as being a waste of money long term, and this option is around $1900 I am told.
2) Replace ONLY that broken package unit with a new, cheap as I can get unit. Would be probably a 2 ton unit. I am told that would run around $6k. This sounds really high to me, though.
3) Remove the current old unit, and rework and replace most of the existing ductwork in the crawlspace (which I want to replace anyway since I believe the old ductwork is nasty inside and seems to be a place where musty smells come from. I smell the smells sometimes in the house, but NOT in the crawlspace, leading me to believe they come from the ductwork). I would then hook up ONLY the other existing ~4 year old 3.5 ton Everest model unit to the downstairs and let it be the only HVAC unit for the downstairs. This may be a bit undersized, but I think together with all the insulating work I did plus the hefty upstairs unit possibly being a bit oversized in my opinion, this is an option that intrigues me. The current two downstairs units were installed in an odd way where the old unit we are discussing replacing was serving half of the downstairs as well as about 800 sq feet of the upstairs. That upstairs load has already been removed from that downstairs unit’s duties. So the result of this would be the current 3.5 ton unit serving the roughly 3200 sq feet of downstairs. I would ask that they do this new ductwork in such a way as to allow the #4 option below to basically be a drop in installation should this scenario prove to be asking too much of the 3.5 ton unit. This reworking / replacement of the ductwork would be about $2k I think.
4) Completely replace the current downstairs units and all ductwork with the exact same 5 ton Trane xr17 and S9V2 furnace in a pancake unit in the crawlspace. This is what I intended to do in the first place, but since funds are limited I now wanted to go through these other options before biting this bullet. $13,500 for this including the whole house air filter / UV light / two zone system.
Thanks for any help on this and my other questions in the last month!!
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