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Community and Q&A

Replacing old AC with a heat pump

jaminh | Posted in Mechanicals on

I have a 2.5 ton AC in my 90s house on the border of zone 5/6a that is getting old so I am trying to come up with a replacement strategy. I’m trying to slowly electrify things so replacing it with a heat pump seems like an obvious choice. Using the heat load estimation calculation here and based on runtime data from my thermostat is looks like my design heat load is around 36-38kbtu. I see I could find a cold climate heat pump that would cover that on its own, but I think my limiting factor is my ducts. With my current AC set to 350cfm/ton my tesp is already over .8iwc (I think it is around .9iwc, sometimes gets up over 1iwc if the filter gets dirty). I assume trying to rework the ducts to accommodate a 3 ton heat pump would be cost prohibitive? I was thinking it might make sense to instead just size the heat pump for the cooling load which I assume would still cover most of my heating and I would just use the existing gas furnace for colder days. I imagine another option would be to split my second floor and the rest of the house and have two heat pumps for each zone, but I think that would probably also mean conditioning the currently vented attic so I could put the air handler up there for the second floor, which I would be concerned is a bigger project than it is worth. Anyone have some insights as to what would be the best option here, or maybe an option I haven’t considered?

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