what size and eff is existing furnace? your biggest challenge may be finding one with correct size for a small footprint like yours. also where is your furnace located? you need a side exit from a crawlspace/basement to take a high eff condensing type furnace. I assume from your location that heating is more important than cooling. what is your electric rate? is townhouse an interior unit or outside unit.

lots of questions. sorry.

I have always thought the spring and fall were the best times to purchase new HVAC-certainly not in the dead of winter or an emergency/breakdown situation.

pricing can be all over the place and depends on market/competitive forces at work in your area. you can pay just about whatever you want to pay. keep in mind there is alot of HVAC junk out in the marketplace and I've always believed that you normally get what you pay for. I would want to take advantage of the fed govt tax credit that is scheduled to expire end of year.

IMO

Delaware just enacted a rebate for both the furnace and a/c. Some manufacturers (ie:Carrier/Bryant) have extended their spring rebates through August. And then there is the Fed Tax Credit (up to $1500) that is available.

Tiger is right that the best time is usually spring or fall. Demand is less and they need to keep their technicians/installers busy and there is less demand on the equipment so they are more likely to discount the price or have rebates. Rebates in our area normally start around September.

I am just a homeowner but was where you were not long ago and have been researching it. This is a great site to find things out.

The starting point though is to have an estimate done and then start asking specific questions. You want at least three estimates before you are done, but it is good to have an idea what your equipment needs are before you get them. You will want to know whether you want low end, middle or top end equipment. If you want to take advantage of the tax credit you will likely need at least a upper middle to top end furnace. The furnace will qualify you for the credit if it meets certain energy efficiency criteria.

But for starters, just have someone come in and ask them to give you their best opinion on what you need. Most will determine the route that they feel give you the best value.