I just bought a house in Las Vegas built in 1951. It has a split system of 125kBtu gas furnace (80% AFUE)with 5 ton (10 SEER) condensing unit. The system appears to be about 7 years old.
The system cannot adequately heat the house on a night where the outside air temperature is 28.
Apparently the problem is that the two return air grills in the house are vented directly (no duct work) to the crawl space and the updraft furnace is directly mounted over a hole in the garage floor directly above the crawl space, thereby making the entire crawl space the return air "ductwork" for the system.
I measured the inlet air temperature at the furnace blower to be about 35 on a cold night.
I have had two HVAC contractors out. Both suggest a whole new system horizontially mounted in the attic with all new duct work and new ducted cold air returns in the ceiling.
The price for the new systems is heart stopping.
Apparently no one is willing to run real duct work through the crawl space and attach it to the existing furnace (Why?)
Can anyone offer another suggestion ??
Thank you. Happy Holidays.