This is the biggest area where a house will lose/gain heat/cold pending the season and make your hvac system work harder. 

like some friends I have say "Its Party Heat in here!

@Mike Hicks the crazy thing is I wasn't even gonna offer her anything after I saw that the house didn't have central AC/heat and it wasn't in a neighborhood I liked.

If you have any capital expenditures (roof, heating/cooling etc) within the next 5-7 years the I would say no to this deal.

I know the house has new hot water heaters and new multizone heat.

You do have think long now as most markets a pretty heated

The market is quite heated now, therefore you must be cautious and have a plan B.

He is great and found a hairline crack in a heating unit that no one else would have found.  

The entire area has been heating up massively over the past few years as all the tech in Seattle is bringing values up in the region.

., replace roof & siding (a few years left in them), 2-zone heat a/c, all new windows (originals still there) and generally take care of the big ticket items now while interest rates are low for the permanent financing, or would you go as cheap as possible to pay down the purchase quicker, while risking getting nickeled and dimed (usually this means out-of-pocket) on repairs for and well as more expensive refinancing in the future?