I have never seen a gas fired boiler with a forced hot air system. Are you sure the boiler is producing the heat for the forced hot air system? I would love to see pictures of this.

I am assume the boiler is very old and probably very inefficient. My suggestion would be to remove the boiler and install a modern high efficiency furnace. It may mean you will need a stand alone hot water heater.

You need a contractor to evaluate the duct work. It must be the proper size otherwise you are wasting money on new equipment. You can keep the asbestos as long as you don't disturb it. However if you have the budget it would make sense to remove the old duct work and asbestos as part of the new furnace installation.

I'm not sure if the boiler's producing the heat or not, but I didn't see a separate furnace. The ducts were enormous, or at least the arms coming out of the furnace/boiler were. The asbestos was intact except for one small area where it looked like duct tape had been applied and was now peeling in about a 2" square section. My preference would be to leave it alone but I'm not sure if we can because of that one area. Unfortunately I didn't take pictures, but we will be making another visit before we make an offer so I'll get some then.

I assume this is the original boiler so I'm betting it's very inefficient. It had a door on the front that made me wonder if it was originally coal-fired.

I'll call our contractor and see what he recommends. If we do have to remove it, at least the basement is walk-out so it won't need to go through the house.

We saw the house again today. I could not find a furnace (the basement's not that big, so I doubt I missed it) and the boiler was warm to the touch. I couldn't get the door on it open, though.

There are two boilers, I guess. This is the one you see when you come down the stairs.

This is in the next room, behind the wall on the left in the first picture.

Closer look at the front.

There are actually two spots where what I assume is asbestos has been disturbed. My preference is still to just tape that and leave it alone.

How does a converted boiler work as far as filters? Does it have them at all? If we make an offer we'll have to ask the seller how it works because this is a new one on me.

Actually, looking at this I'm wondering if it's a boiler. This is not my area of expertise, but it would make a lot more sense if this were just an old coal fired furnace converted to GFA.

That is quite a contraption you have there. It does look like a old boiler which has been converted to natural gas. I don't understand how the air flow works. Is the fist picture an independent blower and return? Is the return air being fed from the basement?

If you are serious about this house, then I suggest you hire an HVAC contractor to come to do an inspection and assess what you have and what it will take to install a modern heating and cooling plant. This set up has to be very inefficient. I would not spend any money trying to modify it for AC. You should also bring in an asbestos abatement company and get a quote of how much it will cost to remove the exposed duct work.

The good news is you have natural gas. If you are going to install AC you have to verify if the electrical service can support it. The bad news is it is going to cost money, but perhaps you can negotiate a better deal with the seller. The whole set up with the asbestos looks dangerous to me. I would not feel comfortable using this set up. It needs to be addressed before the heating season starts.