90% efficient furnaces are kind of the low end of the spectrum of product on the market now, at least in my area of the USA. My 20 year old furnace is rated 94

90% efficient furnaces are kind of the low end of the spectrum of product on the market now, at least in my area of the USA. My 20 year old furnace is rated 94% efficient. Pretty much every condensing gas furnace now is going to be well over 90% efficient. Even modulating furnaces with 2:1 or better turn-down ratios can maintain over 90% efficiency when running below rated output. Locally it's not worth DIYing a heat pump install. The tax incentives and rebates easily cover the cost to hire a licensed and insured HVAC company to do the entire install for you, plus then you get to choose from a much wider selection of heat pump models which likely enable buying something better sized for your need and more efficient.