Ask your insurance carrier for both your new and old house. 

Mine was $9,000 with Rocklin Heating and Air for a single stage system by Carrier, in April of 2019.

We have had insurance carriers refuse coverage due to a sagging roof in otherwise perfect condition.Plumbing: cast iron water & waste pipes will be corroded & could fail especially if your rehabbing & retrofitting new PVC.

A different carrier might provide service at that location but for me that would be a deal breaker.

Kevin, like @John Mocker mentions, we have a lot of carriers who are comfortable with it.  

even if you are "fully responsible", YOUR insurance won't pay 100% of the damages to someone else's property because your property insurance covers only your property. your liability policy would kick in if you are found "guilty" of damaging someone else's property (and will almost never cover all damages - this is not an auto accident) but their first line of defense is their own property insurance. all that aside notifying your carrier is a great first step as they will defend you if need be!

Hi this is your mail carrier, I am interested in purchasing your home..... 

He shops carriers to get the best coverage for the best price.

----------------------------------Below is the quote for fixing the airconditioner by replacing coil and condenser.4ton Rheem/Goodman Brandnew coil and condenser10 yr warranty 1yr labornew condenser padnew wipe1gl masticroll of silver tapenew condenser padroll of silver tapepvc couplingcopper fittingcondenser switchpannew t(stat)Cost: 3800----------------------------------replacement option 1-----------------------------------Carrier Brand Full System20yr warranty furnase and coil condenser10yr warranty A/C1yr labor replace break outsidenew condenser padroll of silver tapepvc couplingcopper fittingcondenser switchpannew t(stat)Cost: $7500-----------------------------------replacement option 2-----------------------------------Rheem Goodman Brand Full System20yr warranty furnase and coil condenser10yr warranty A/C1yr labor replace breaker outsidenew condenser padnew wiperoll of silver tapepvc couplingcopper fittingcondenser switchpannew t(stat)Cost: $6800---------------------------------------

There are rood exclusions within some carriers that are meant to protect the company from accepting a $20-30k claim as soon as you are their client.