Good grief the FIRST and only thing you need to be concerned with ( yes I know this is a old thread/posts but I have to respond to this ) is what in the world is a 4 ton doing in a 1300 sq ft double wide???????????? If you dont have moisture problems your house must be blessed by god himself. That unit is ENTIRELY too large for your home.

Here in California the regulations require that a different company test the duct system for leaks (it can not be the outfit which installed the heating/cooling system) this is a good practice imo. wish we had those standards in place here. flex people diss hard pipe hard pipe people diss flex. here is my experience. flex leaks at the plenum and the supply box. hard pipe leaks at all 90's the long seams and all connections. most hard pipe that is unwrapped has dust marks at the leakage sites where air has moved thru insulation. flex usually is dirty at plenum and supply box. hard pipe is more expensive, and is wrapped when installed, leaving little time to mastic seal. and once it is covered up...who knows how well it was sealed? sealed hard pipe is a beautiful thing. flex does have more resistance to air flow, but the ducts are usually sized to overcome the resistance. pros and cons for both. try to avoid the companies that bad mouth the other ducting. make sure that connections are mastic sealed. not duct tape, foil tape. paint on mastic or mastic tape. I test both types, unsealed hard pipe leaks much more than unsealed flex due to the sheer amount of leakage areas. both can be well sealed. just takes the want to do so. best of luck

Thanks very much for your reply. The upstairs is 1100 sq ft. The main level is the same, as is the basement. The upstairs furnace is 50 BTU. The heating is natural gas. There is ductwork in the basement that supplies the main floor. The basement is unfinished currently. That may change. There are six vents upstairs with one return in the hall area. The return is 12x24. There are eight vents downstairs with one return in the hall area. The return is 12x24. I was told that the unit upstairs had a leak/crack in the compressor that could possibly leak carbon monoxide. There are marks on the outside of the unit that looks like burn marks. The heating unit performed fine the last time we used it before we found out about the burn marks. It is about 25 years old and about 8 SEER. The cooling unit seems to run almost all of the time in the summer. The downstairs unit also performs ok but needs a serious duct cleaning due to water from a pipe bursting in the kitchen getting into some of the ducts. We haven't used it in quite a while. The house has humidity problems sometimes (window condensation and my indoor hygrometer can get near 80% in the summer but is around 50% in the winter) and we would like a system that can take care of that and be more efficient. The upstairs unit seems to run all of the time in the summer. The stat is usually set around 75. I was told that 16 SEER two-stage would fit the bill. Other ac companies told me I needed nothing more than the typical 13 SEER. Some family members have asthma and I also want something that will help with that. How can I tell if my ductwork really needs to be enlarged? Thanks much for your input

Pieinsky & Bob Brown are on the mark when it comes to high SEER units. I ask any rational person, does it make sense to Rate season energy efficiencies based on an 82-F outside & 80-F inside temps which is a mere 2-F degree differential. A mere 2 degree temp drop virtually eliminates the latent load humidity problem. I know they claim with a Variable Speed Blower, etc., etc., they can somehow get thwe humidity down. Well, maybe but prove it to me in those conditions. The SEER of a system is determined by multiplying the steady state energy efficiency ratio (EER) measured at conditions of 82°F outdoor temperature, 80°F dB and 67°F wB indoor entering air temperature by the Part Load Factor (PLF) of the system. (The PLF is supplied by the government.) Consider the criteria being used for their SEER formulas. Air conditioner EER ratings, and BTUH Tons of Cooling Capacity ratings on Air Conditioning units are rated at an outdoor temperature of 95°F, and an indoor 80ºF dB 67ºF WB or, a 50% Relative Humidity. The larger coils & smaller Btuh compressor cause a higher pressure/temperature resulting in increased Volumetric efficiency for the smaller compressor's capacity at 82-F ambvient & 80 indoor temp. At 82-F outdoors our homes in the Midwest are well into the comfort zone until late afternoon, etc., fans could keep us comfortable. Rate the SEER at 95, 100 & 105-F ambient & 76-F indoor dry bulb with a 55% Relative Humidity & watch the numbers SHIFT! Additionally, how about a 62% outdoor Relative humidity, with those outdoor indoor temp spreads & the high SEER's higher pres/temp E-Coil it would never control the humidity. Is it against the law for contractors' to rmove the smaller compressors & install an oversized compressor like we used to have 40 years ago? udarrell _ 2007 Here is a link that might be useful: udarrell.com