Unfinished basement ceiling/rim joists – guidance on best insulation + air sealing approach?
Background: I have a mostly unfinished basement area that is about ~550 SF. Only part that is “finished” is plaster ceiling that has mutliple holes in it from running electrical, gas, etc. over the years. 1930’s colonial in Massachusetts that gets 100% of space heating from ASHP mini splits. This unfinished basement room used to have oil boiler + oil tank (recently removed). No space heating in this room, just small amount of waste heat from gas water heater (will be replaced by ASHP water heater eventually). If temperature gets very low in this area and I’m concerned about pipes freezing, can open door to finished portion of basement served by ASHP. Area directly above unfinished basement is kitchen + office (frequently used rooms). There is no insulation in basement ceiling or any air sealing along rim joists as far as I can tell/know. I have no interest in ever finishing this basement area.
Question: Does anyone have advice on best insulation and/or air sealing approach given my situation? Is it worth ripping out the (already damaged) plaster ceiling to enable air sealing and/or insulation? Utility EE program in Mass (MassSave) only covers the rim joist perimter. Sounds like they use spray foam to air seal around any exterior penetratoins + 6-inch fiberglass batts in each “bay” (I’m not totally clear what they mean by bay – window bays?). That being said, I’m willing to invest $$ in removing plaster ceiling + either DIY or hire pro to do more significant insulation and/or air sealing work if it has significant EE benefit (even without penciling out necessarily). My understanding is that basement ceiling insulation is often frowned upon given waste heat from boiler/furnance, but that is not a concern in my situation.
Thanks for any advice!
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