Dear Jim: We added a room, but our central air conditioner doesn’t cool it well. Our second-floor master bedroom also does not stay cool. Does it make sense to install a window air conditioner or a mini-split system? – Kyle F.

Dear Kyle: The cooling problems you are having are not uncommon. This is particularly true for second-floor rooms. The cool air-conditioned air is more dense than warm air, so it tends to drop to the first floor.
Also, second-floor ceilings are exposed to the hot underside of the roof.
For both your new room addition and your second-floor bedroom, installing a mini-split air-conditioning system is more efficient and effective than a window air conditioner. The only drawback is a mini-split system is more expensive to install initially and cannot later be moved to a different room.
I have a two-story house with a central heat pump. I recently installed an LG Art Cool mini-split system for my master bedroom. I selected the smaller output 9,000 Btuh model which has an efficiency of SEER 28 and inverter compressor technology. My central heat pump is SEER 13, so my Art Cool model is twice as efficient. I chose the heat pump version so it can also heat efficiently during the winter.
A window air conditioner has all the components – compressor, air circulation fan, condenser fan, etc. – in the cabinet in the window.
Even though it is insulated against heat flow and sound, it still is not ideal for good efficiency. The newest ones are fairly quiet but can be annoying in a bedroom at night.
A mini-split system is very similar to a central air conditioner or heat pump with the condenser fan, coils and compressor in an outdoor unit.
Some models allow the outdoor unit to be placed up to 100 feet from the room. This virtually eliminates noise from getting indoors at night.
Instead of having the indoor cooling coil in an air duct system as with your existing central air conditioner, the coil is mounted in a fan unit on the wall or ceiling of the room. It is connected to the outdoor unit by refrigerant and electric lines. Only a three-inch-diameter hole needs to be cut through the wall. The condensate drain goes out through the same hole.
Mini-split systems can be used to air condition an entire house by installing indoor wall units in several rooms. The cool air will circulate throughout the house. This is commonly done in houses using baseboard electric or hydronic heat which do not already have a heating duct system.
In addition to the high SEER rating, installing a mini-split unit allows for zone cooling. For example, in my case, there is no need to keep the downstairs cool all night when I am sleeping in the bedroom. My mini-split system allows me to set the central thermostat higher at night to save.
The inverter compressor provides for variable cooling output. Once the room cools down to the thermostat setting temperature, the inverter compressor speed slows to keep the room at that temperature. The hand-held remote control has many modes of operation including a dehumidification setting.
Dear Jim: I need new siding on one wall of my house. While the old siding is off, I plan to install foam sheathing. Is it important to follow the nailing guide or can I use more nails to make it extra strong? – Keith P.

Dear Keith: It is best to always follow the manufacturer’s nail pattern guide unless it is less than your local building codes. Foam sheathing, although rigid, is not very strong so more nails than necessary does not create a stronger wall.
Actually, more nails can be counterproductive because each nail creates a small thermal bridge from the interior to the exterior. By using excessive nails, the overall insulation value of the wall will be reduced.
Dear Jim: I am building a house that will use passive solar heating. It will be a ranch-style house with many south-facing windows. What is the best way to plan the rooms for the best natural heat circulation? – Faith G.

Dear Faith: An open floor plan is generally best for passive solar heating. This allows the solar heated air, usually on the south side of the house, to circulate more freely throughout the rest of the house.
Design the interior walls with large openings between rooms. For efficiency and a contemporary look, build curved walls and smooth transitions between rooms. Bendable drywall is ideal for this. Since it is thin, two layers will be needed.