What is your climate?
You should consider a new 95% efficiency 2-stage furnace if you get cold winters. You should insulate your attic if its badly insulated.

If your home is 2 stories you will have problems keep the temperatures on both floors balanced unless you either have a seperate system on each floor or get zoning. At the bare minimum you could get a manual damper installed so you could manually regulate how much heat/cool goes to the upstairs.

If your a/c is old you should replace with a new and highest efficiency single stage. I personally recommend spending a little more for a heatpump. You would then have a dual/fuel (aka hybrid heat system). This type of system could allow you to save energy and be extra comfy in both mildly cold and very cold weather.

A humidifier is good for running the gas furnace since the very hot air is dry. When you run in heatpump mode you don't have this problem.

Mgedid

Describe your typical climate/weather both summer and winter.

Age of your home?

Sgl story or two story?

How would you describe the insulation qualities of your home?

What size and efficiency is your existing furnace?

The problem with the two rooms is most likely one of ductwork sizing/design along with insulation properties. It is doubtful that new HVAC
would solve or even improve this situation. You need a good dealer experienced with ductwork and insulation to evaluate this problem and offer suggestions for improvement. Your ductwork system is how old? How is it insulated? It may just need to be balanced.

I would never recommend a HP without knowing your nat gas and electric rates and probably would forget it for upstate NY.

Post back.

IMO

Consider hiring an energy auditor or rater to identify the low-hanging fruit for energy savings. (Windows are not usually the best place to start.) Hire someone that does not do other types of work so they are unbiased in finding a solution. Find one via Resnet.

Have you examined your duct system? You might have serious leaks to the rooms you are having trouble with.

and along with the duct leakage..which you do have..
the house leakage.
trying to heat and cool a leaky box results in
hot/cold areas.
air sealing the house, evaluating & sealing the ductwork
are the two least expensive things to do with an immediate
effect on comfort. you can diy a lot of this yourself
if you know where the leaks are.

blower door testing of the house for leakage, and duct testing also would be the place to start.

invest the $ & labor here first and then decide if the
equipment is the problem. even if you change out equip
the air you are heating & cooling will come into a tighter
less leaky house. you'll feel the difference.

we can diy you thru the mastic sealing of ducts and caulking inside. for free! LOL!

best of luck

Wow, thanks all:

The house is indeed a leaky box. It's 50 years old, 2100 sf, 2-story (no basement, no attic) deck house with exposed rafters. All main living areas kitchen/LR/BRs are on the second floor. The furnace size -- not sure what, but the only guess we've had on the efficiency was that it started at 80% and is likely to be at 60% efficiency now, 30 years on.

We think there is most likely inadequate insulation in the ceiling. The walls are insulated, but we have a lot of odd-sized, double paned windows. An energy auditor did say that it was unlikely the ceiling insulation would solve everything with the percentage of windows we have, and that additional wall insulation would most definitely not be of value. But both the exposed rafters and the odd-shaped windows are part of the architectural "value" of the house, and we do love them, and think that the people we eventually sell to are likely to love them as well.

The exposed furnace room ductwork is pretty shabby looking, with obvious leaks out of the octopus-like central heat source, and it's all uninsulated. The furnace room with all these exposed ducts is always cozy and warm when the heat's on, and perfectly cool when the a/c is on. The two bedrooms that we have the most trouble with are farthest from the furnace in the house, and they are on the side of the house that appears to be the most shaded.

As for what is behind the walls, and the type of work that energy rater is describing, I'm happy to ask a professional to work on it, but I don't know how to choose a service person to do it if nobody will return calls.

Also, how do we know who is a dealer who specializes in ductwork?

We are in southern westchester, new york.

many thanks,

mgedid

It seems like you have both duct design and equipment questions going on. This makes solving the problem tricker.

Previous poster is correct in that new and even larger sized equipment will not solve the comfort problem if the duct design will not allow the airflow to reach the space in the necessary manner. Think of air like water through a pipe--if the pipe is too narrow and restrictive, turning up the water doesn't do much to get more water flowing.

You need to find a good experienced dealer who can help solve your problems. You might call 2 or 3 distributors in your region (York, Trane, Carrier, Lennox) and ask if they can recommend a dealer for your area that is good at duct design and problem solving. Then when calling these dealers, say you are not in a big hurry, and want to have their most experienced guy who can help you the best be the one who comes out to your house.

Best of luck

What are your winter heating bills? It does help a little to know your baseline. If it is $4000, then you absolutely should be getting a new furnace as it will pay for itself very fast.

I'm a little confused about layout. Where is the furnace - if you don't have a basement or attic? I also mention this because I am fairly paranoid and you have quite an old system in a house with kids. My last house had a system in a crawlspace and it didn't have the best exhaust mechanism. It was just an 80% installed in 93. The POs had a CO detector in the room above it when I bought in 2004. It didn't go off but I wasn't crazy about the idea of needing one.

If you have a furnace in a crawlspace with uninsulated ducts running at 60%, you've got some low hanging fruit. My big question is that the bedrooms are on the first floor so they would be close to the furnace. So that is why I ask, where is the furnace?

Knowing the actual location of the furnace and how the ductwork is run might help us guess on the kid's rooms issues. I am going to guess right off that you should be replacing everything from a comfort and efficiency standpoint. You could bandaid some comfort, but the payback for the efficiency standpoint will be pretty fast.