Originally posted by jrminator
One of the contractors who has bid on replacing my a/c and furnace tells me he can use a smaller a/c unit because of using zoning with automated dampers. He has specified a 3 T unit when the gain is about 40,000 BTU/H. The gain was calculated by doing a manual J take off. We talked about the difference in the gain and the unit he sized and he tells me he would use a 3.5 T unit if we were not using zoning. I don't buy it. It seems to me that he needs to balance the gain with an equal a/c output; zoning will just distribute the cooling capability more evenly through the house. I have a 3 T unit now and it can barely keep up on hot days. He also tells me that using a system with R410a allows him to specify a smaller unit. Again, it seems to me that a/c output is output no matter how you get there. Any comments about this would help end my confusion.
In regards to your comment, "it seems to me that a/c output is output no matter how you get there", that is correct. It doesn't matter whether you have a 3 ton R-22, 3 ton R410A or 3 ton Ammonia system, you have 36,000 btu's of cooling capacity.
In regards to zoning, he MIGHT be correct. If parts of your house do not need as much cooling on the hottest day, during the hottest part of the day, zoning can allow you to use a smaller unit. For example, if the bedrooms do not need the cooling during the heat of the day, or the north or east sides or the downstairs, etc, you now have all 3 tons of cooling being directed to the zones that may only need 2 or 2 1/2 tons. The 3 ton will cool those zones down quicker, because none of the conditioned air is being "wasted" by going to unoccupied rooms which could have the zone stats set to a warmer temp.
It's been stated by many people, including me, in other threads about the cautions to keep in mind when it comes to R410A systems. Half the guys seem to love 'em, and the rest of us are unconvinced at this point. Like I said before, I will not recommend the R-410A systems, yet, to any of my friends or relatives. For reasons, do a search for Puron, or Ultron, or R-410A.
The more I learn, the more I realize I've got more to learn.