Dear Jim: We are empty-nesters now. Is it wise to move a portable air conditioner among rooms instead of running our central air as much to cool the entire house? – Kari K.

Dear Kari: Using a portable or air conditioner is a good idea especially when two of you are going to be in the same room for an extended time. This also is effective with central air-conditioning. Even though the cooling efficiency of a newer central heat pump is generally higher than that of a portable model, using portable one can save money overall.

Run the portable unit to cool just a few frequently used rooms to the comfortable cool temperature you desire. Raise the temperature setting on the wall thermostat for the central heat pump four or five degrees higher than normal. This can provide a 10 to 15 percent electricity savings without a major sacrifice in comfort.

During moderate temperature weather, turn your central air conditioner off completely and use just the portable unit. A sizing rule-of-thumb is an 8,000 Btuh model should comfortably cool rooms up to 350 sq. ft. and a 12,000 Btuh model should cool a 550 sq. ft. area. Both plug into a standard 120-volt outlet.

Portable air conditioners are particularly convenient to use because you can roll one from room to room. With this feature, one portable unit can be used to keep different rooms cool depending upon which room you are using. It is best to have one for each floor of a two-story house.

Portable units operate similarly to a typical window air conditioner. The internal rotary compressor, evaporator and condenser function in the same way. The primary difference is it is on castors and rests on the floor. The sound level is similar to a typical window air conditioner so they work well in bedrooms.

There are two basic designs of portable units. One design uses a single duct to the window adapter. This is the simplest system and works well, but it does draw some cooled or heated room air to the outdoors. I use a one-duct model, with a remote control, in my second-floor bedroom to precool it at night. Then I set its thermostat higher so it does not come on much overnight.

The other design uses two ducts and is more efficient. All of the air flowing through the condenser (which carries the heat away) is drawn from outdoors and exhausted back outdoors. With two ducts, no already-conditioned indoor air is being exhausted outdoors. This is more energy efficient, especially when operating a heat pump model in the heating mode during winter.

Another feature to consider is how the condensed water is handled in the cooling mode. Evaporative models mix the water with the air exhausted

outdoors so there is nothing to empty. Other models, which also function well as dehumidifiers without cooling much on “Dehumidify” setting, capture the water in a small tank which you must empty. This is basically distilled water in the tank which can be recycled to water house plants.

Select a model with several blower speeds and adjustable directional louvers. When cooling, adjust the louvers to direct the cooled air up at about a 30-degree angle. The cooled air blowing out is denser so this keeps it from settling at the floor level.

A flat adapter panel is used to connect the portable unit to a window with one or two five-inch-diameter flexible and collapsible ducts. This is where the heat, which is pulled from the room air, is exhausted outdoors. The window adapter and ducts, which must be moved along with the portable unit, fit most easily in single- or double-hung or slider windows and sliding glass doors.

Use one by one-inch foam weatherstripping to seal the window edge against the panel. Hollow round foam pipe insulation also works well. Use tape or glue to secure the foam to the panel to simplify moving among windows. To use with a casement window, you must make a triangular top and bottom end caps to seal in the window opening.

Living alone, I use a portable heat pump model in my own home/office for year-round savings. Portable heat pumps, which look identical and operate similarly to a portable air conditioner, also provide heating during cold weather. This efficient heating source can produce up to 12,000 Btuh from a 120-volt electrical outlet. Most electric space heaters produce only 5,100 Btuh.

The thermostat is built into the handheld remote control so it senses the temperature where you are located. This is an advantage because you really need to have it comfortably cool precisely where you are in a room. With sun shining in windows on a hot afternoon, the temperature can vary significantly throughout a large room.

The following companies offer portable air conditioner/heat pumps: Danby, (800) 263-2629, www.danby.com; LG, (800) 423-0000, www.lg.com; Soleus Air, www.soleusair.com; Sunpentown, (800) 330-0388, www.sunpentown.com; and Toyotomi, (203) 775-1909, www.toyotomiusa.com.

Dear Jim: I am having a problem with nail pops from the drywall on the ceiling. There seem to be more and more of them. I tried to fill them with compound, but it pops out again. What can I do to stop this? – Rachel H.

Dear Rachel: Nail pops can have several causes, but the end result is the same. The drywall compound over the head of a nail pops off exposing the head. Just putting more compound over the hole will not work for long.

If you push on the drywall, you will probably feel it move. Drive some additional drywall screws around the pops to make sure the drywall is secure to the framing. Drive the old nails in deeper and fill over the heads with compound.

Send inquiries to James Dulley, Newspaper Name, 6906 Royalgreen Dr., Cincinnati, OH 45244 or visit www.dulley.com.