I think that you know the answer. The sun room is meant to be used when the weather permits. You could add a lot of days to its useful season by insulating the walls and floor if they face unconditioned space. Probably, i would be less expensive to warm it by putting a fan on the floor to blow the cool air near the floor out, than to use electric heaters.

The Butler't pantry is supposed to be used to store stuff. Keep your root veggies in there.

I have a couple of suggestions. Before you add AC, have an experienced energy rater evaluate your house. Make sure you are not going to freeze some pipes if you close the doors to those rooms.

That house needs to be evaluated, as ionized said. Before you even think about redoing the HVAC, the envelope needs to be upgraded as much as possible. Insulation is much cheaper than a larger heating and cooling system and big energy bills every year.

Do you know what the insulation situation is?

Actually, I don't knoww what's there. I know it's pretty comfy for the most part, and the PO put on a new room and re-did some of the ducts. She also used a ton of that expanding ffoam to insulate the spaces around the windows when she put in the Andersons. I've been thinking about contacting the gas/electric company to see if they offer evaluations, just so I can get a good overview of what's in place.

I don't *think* there would be any problem with freezing pipes if I keep those rooms closed -- I can't imagine how any are routed thru those spaces. (Half the sunporch is above the butler's pantry, the other half is over the open back porch.)

Reading thru a lot of threads here I've made a list of some things I know I can do; check switch plates and baseboards for drafts and cold spots, and I'm making a weekend of checking spots that I know a problem areas.

I've been enjoying having the extra fridge space in the butler's pantry over the holidays, but I did have to move tender plants out of the sunporch. Luckily there's a south facing room down the hall which gets tons of light.

Bad proof reading -- I meant to type that the PO put on a new *roof* and redid some ducts.

She also finished the third floor, and there are vents in both rooms. But the home inspection notted there was nothing coming out of them in July. when I asked about that at the closing she said she "was sure they work fine" -- they need to be checked out this spring. May be something as simple as a vent closed somewhere down the line, but I don't know much about HVAC.