Ask for:
- a load calculation
- duct measurements vs system capacity = adequate ?
- do they flow nitrogen while brazing ?
- do they perform a nitrogen leak test + proper vacuum with a micron gauge ?
- proper commissioning of the unit with a report after completion
Make sure you get a good filter. 4in pleated, MERV 8 or higher, something along those lines.
That's a start.
I want higher efficiency, but not sure I can afford the highest efficiency equipment. Existing furnace is an older Lennox. No A/C currently.
I want reasonably quiet equipment. If it has to be near the bedrooms, I want it to be very quiet.
Comfort is a big concern. House is uncomfortably cold in the winter with the bedroom areas being the coldest. In the summer, the master bedroom is very hot (faces southwest) and is uncomfortable for sleeping.
House is insulated, but needs more in the attic.
I avoid big box stores as a general rule. I have a couple of contractors in mind, but need to know what to ask.
I would take these two blocks of information and start here.
A load calculation is a Manual J. This needs to be room-by-room to size the ductwork.
I would also add the requirement for a Manual D and a Manual S.
Manual D sizes the ductwork and Manual S sizes the equipment. There are independent consultants that will do this work for you, for a fee. In my opinion, it would be beneficial for you to pay to have this done, and provide the information to the contractor as a basis for comparable bids. There are people that provide these services and do not perform installations, so there won't be a conflict of interest. You will have to provide drawings of your home and construction information.
Overall poor workmanship, noisy when it ran, wrecked my attic insulation during the install. It did heat and cool the house, though.
Poor workmanship: ask to see pictures of installations.
Noisy: Ductwork can be well sealed and not flow air well at all; some of this is due to "cap and tap" duct practices and undersized ductwork. Low end (builder's grade) equipment is usually noisier than upper tier models- no matter what the brand is.
Wrecked attic insulation: Impossible to avoid if one chooses to put ductwork and equipment up there. The ductwork should be within the conditioned space envelope. Attic ductwork is a poor choice and should be avoided at all costs. Ductwork outside of the conditioned space may trigger additional testing requirements (Residential Energy Code) if this is a permit job. Think about this: the attic can easily exceed 140 degrees in the summer, and there is ~55 degree air in that duct (at the air handler- higher temperature at the registers). The building requires say R-40 but the ductwork may be lucky to get R-8. It makes no sense at all.
A mini-split system with a single condenser and multiple heads will provide the highest efficiency, but the equipment and maintenance costs will be high.
A high-SEER split system requires proper airflow to attain those SEER numbers.
The air filter needs to be designed into the system.
Traditional residential split system fans have a 0.5" of water column spec for total external static pressure. That is the resistance to airflow generated by the (wet) AC evap coil, air filter(s), all ductwork and registers/grilles. It isn't a lot to work with, and this is where coil selection, filter selection and ductwork airflow/design will make or break the system.
