Long range HVAC planning.
We're trying to make some long term decisions for heating and cooling our house. (and adding humidity in winter) It's a 1400 sq ft Cape, in Massachusetts. We have very cold winters, and hot and humid summers.
Our house currently has gas heat, forced hot air. We don't have central air. There's no humidity control.
In the summer, we use a few window air conditioners. (and, of course, fans.)
In the winter, we use a room-sized warm air humidifier. With the forced air heat, this seems to do a good job of getting the humidity spread throughout the house. It's labor intensive: it needs to be filled several times per week, and cleaned every week.
The gas furnace is an oil conversion. The conversion was done about 5-10 years ago (two owners ago). The 'gas part' (I'm blanking on the right name for it) is rented from the gas company for about $15/month. The whole furnace is sealed up, so it's impossible to inspect its condition. From what I've been told, these units made in the 70's were made right, and could last a very long time. Or the heat exchanger could fail tomorrow. We're kinda figuring it has 2-5 years left in it.
Would it make sense to add central air to the current setup? Or would it be wiser to wait (for it to fail?) and replace the furnace at the same time?
Also, what options are there for adding humidity to a forced hot air heat system? We're looking for something low to no-maintenance.