[scott_s]

I had heat pumps installed in my house last year, to replace oil-based heat from baseboards. We have no drainage lines on the the front of the house, and only one bundle on the back. It follows the roof line, and then down a corner of the side of the house. So, yes, you will need drainage lines, but no, they shouldn't have to be all of the exterior. They should be able to be placed in an acceptable way. (Similar to, say, gutters.)

On the savings side: I think we're about even compared to oil. But I'm okay with that: we didn't have any air conditioning at all in the house, so we had no duct work. (We bought the house at the end of 2022 like this.) Since we were already doing significant work to install the duct work and get a new air conditioning system, I wanted to make them heat pumps to get off of oil. I think in the long run, we'll save money. I eventually plan on installing solar panels. And even if it's a wash in terms of money, I'm care about climate change, and I want to do what I can to electrify my house.

edit: After looking at other comments, I should clarify what we have. We have two condensers outside, and three air handlers inside. It acts like "central air", for the most part. We do have one mini-split, for the main bedroom, as we could not get ducts to it. My point here is that "heat pumps" do not necessarily mean "mini splits." My house is almost entirely centrally heated and cooled through duct work.