Hello everyone, my last post was in Jan 2007. Now I'm back for a new project, and it's great to see some of the old names here. We do not yet have a good, professional load calc on an architect's design, but we need to chose some good options.
Can a nominal 1 1/2 ton A/C or heat pump be set up to work at a capacity much less than 18,000 BTUH? Is 12.000 or 15,000 BTUH a reasonable target? If so, what specific models would you recommend for compressor and evaporator coil? We are thinking primarily Trane or Carrier, including gas furnace or hybrid heat pump/gas furnace, but also looking for any other good solution.
This is for an expansion of my son's split level house in Northern Virginia. The problem is the new space "feels" like it is too small for the smallest central A/C or heat pump, and one of the bidders for the remodeling threw up a yellow flag. My own "rough," non-professional load calc comes out at 11,100 BTUH cooling with +/-600.
The house has three levels. The main entrance is to the middle level living, dining, kitchen, with its own attic, and there is a den expansion behind that. The lower level to the side and half flight down is two rooms, bath, and utility space. The upper level also to the side and directly above the lower level is three bedrooms and a bath. The new expansion will be above the middle level replacing the attic at 480 sq ft (20 x 24) consisting of a bedroom, bath, and maybe a walk-in closet.
The current HVAC includes a two-stage Trane XL-19i A/C and two-stage Trane gas furnace. This may have the capacity to handle the new bedroom area, but some remodeling contractors get nervous about the modifications to existing structure. The furnace is in the utility space, really a long, narrow closet on the lower level, shared with washer, dryer, and access to crawl space under the middle level. Although the closet shares its wall with the middle level, running a new trunk straight up through a bedroom and over to the new bedroom's attic would be a challenge. Also, we know there is a challenge in balancing air flow to four different levels of a house.
By the way, that load calc for 11,100 comes from the Consumer Reports web site tailored for room air conditioners. I was looking only at total space involved.
We appreciate all the help.