Well my current thread is on the borderline of this thread. Without question I would recommend changing out the whole unit. The new equipment will be much more efficient, for the gas furnace it will be from less than 85% to more than 90%. The air conditioner will also be much more efficient. You will notice a substantial reduction in your energy bills. I can't quote any savings since we have the gas well and there is no meter, and the air conditioning is a new addition and this was 6 years ago. Our unit is a Rheem, and daughter has a 2 year old Trane heat pump that she is very happy with. Both units have been reliable since install with no service calls. An issue I have with the Rheem (and have similar from other people with Rheem) is noise. During startup, there is a audible 60 cycle hum as the blower fan and combustion air blowers come up to speed. Also there is moving air noise when the fan is operating , particularly noticeable with the furnace being directly under our bedroom with a close coupled cold air return duct. Visit a house with similar equipment and pay attention to noise level. For fuel selection there are some combinations available today that weren't a few years ago including heat pump, geothermal in combination with electric, natural gas or propane. Very difficult anticipating the future, but I try to have flexibility. We have backup electric resistance heat on top the gas furnace in the event the gas well pressure is low, which does happen in very cold windy weather. The generator is sized to handle half the electric resistance heat, which means I can heat the house with gasoline, indirectly with natural gas or propane. I do believe in the future we will see brown outs for load shedding of the electric or natural gas, might be a few years, but I am prepared. Some of these are more expensive to install, I would for operating costs maybe double current costs. The heat exchangers today are typically stainless steel, at least that should be required. When these high efficiency units first came out, the many electronic devices were not reliable, but today things have improved considerably. I do stock a spare controller board for the furnace, and a spare pump (small) for the zoning, but have not needed them yet. :) The combustion gas flue to the outside will be sch. 40 plastic pipe and likely exit out the nearest sidewall. Your hot water tank (assuming natural gas or propane) will still be on the existing chimney or metal flue which now will probably be oversized. We changed ours from 5" dia. metal to 3: dia. metal. There are new high efficiency hot water heaters you might want to consider if your existing tank is more than 5 years old. The contractor should provide heat loss/gain calculations to size the unit properly. Experience with the existing equipment should also be used. % of run times in extreme weather should be discussed. Note that the new equipment will be at least one size smaller due to efficiency improvements. Output BTU's and air flow (CFM's) should be compared. Do you expect the house to come to temperature in a short period of time, or is a longer period of operation acceptable where most of the time the set temperatures are fairly constant. Depending on the layout and use of your house, you might consider zoning, where each zone has it's own thermostat and ducts are power dampered. We have the Arzel equipment (http://www.arzelzoning.com/ ), and it is simple and reliable. Their home is Cleveland, Ohio. It is possible to service interchanged heat and cool requests witha 20 minute wait. The dampers are vacuum/pressure actuated from a small vibrating pump and small solenoid valves. Our house has 4 zones : Basement (rarely serviced), 1st floor, 2 2nd floor zones due to the duct configuration. The 2nd floor is normally set to heat 55F and not cool unless we are occupying the area which is almost rarely. If needed, in extreme conditions we can make it comfortable within an hour. William Couture wrote: > Hi all, > > Well, our central air conditioner is dead. The compressor is frozen. > > The system is 15+ years old, and the repairman says that it would be > best to just replace it (parts not available, Freon system). The entire > system would have to be replaced, as the new refrigerants operate at > higher presures. Ballpark (not estimate) is about $3000. > > It is hooked into the heat system, which is gas. It is from 1960, > and he thinks that putting a new AC into an old system wouldn't be > worth it. New systems are much more efficient. This brings the > ballpark figure to about $5000. > > Of course, one problem with new gas systems is the heat exchanger > -- we have a solid cast iron heat exchanger, and a pilot light. The pilot > light keeps the temperature fluxuations down and keeps moisture out > of the sytem. New systems do not have a good, solid heat exchanger, > and do not use a pilot light (thanks, government!) so they get > condensation and rust. Lifetime is about 15 years, a little more if you > are lucky... > > So, what suggestions do people have for a new system? What > brands should I be looking for, what should I avoid? > > Should I be looking at heat pumps instead of traditional systems? > > Anything else that I don't know that I don't know? > > And, in case it makes a difference, I am in Pennsylvania > (New England, the eastern coast) in the USA. > > Thanks, > Bill > > -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist