Dear Jim: My elderly mother moved in with me and she needs cool air in her bedroom. I want to install a quiet window air conditioner for her. What is the best type to get and how big should it be for a bedroom? – Ron J.

Dear Ron: As people age, they often become more sensitive to the heat and cold. My mother is almost 92 years old and she often comments about feeling hot or cold at normal room temperatures. A good quality window air conditioner with full-featured remote controls would be a good choice for her bedroom.

Selecting a window air conditioner with the proper cooling capacity is critical for comfort and efficiency whether you are cooling just a small bedroom or a large family room. If the air conditioner is too large, it doesn’t run very long, so the air is not adequately dehumidified. If it is too small, it runs almost continuously and never cools the room enough.

When shopping for a window model, many salespeople just read a room size from the package. In your mother’s case, this would indicate a unit which is too large. Hers will be used mainly at night when there is no intense sun and the outdoor air is cooler, so less cooling capacity is needed.

Worksheets are available to calculate the cooling capacity needed for a specific room. These take into account the number of windows, orientation to the sun, wall insulation, shades, etc. The salesperson should have access to a worksheet. Fill it out for a more accurate size estimate.

The efficiency of window units is important because running one affects your monthly electric bills. Their efficiency is called EER instead of SEER for central air conditioners. Try to get the highest EER (up to 11.7) within your budget and size range. If you have to spend a little more for one with a higher EER, it probably makes good economic sense.

Some of the full-featured models have various types of sleep or nighttime modes. Some use a soft start and stop design which reduces the noise when thermostat switches the unit on and off. Another nighttime mode runs the unit at a more continuous, but slower and quieter speed for sleeping.

Select a model with a timer control. This allows you to set it to run for any length of time up to 12 or 24 hours depending on the model. A 12-hour timer is usually adequate. Your mother may want to use it for two hours so the room is extra cool when she falls asleep and then it shuts itself off.

Allergies are a common reason people use window air conditioners even if they have central air. All window models have some type of air filter, but you can select models with washable or replaceable super-efficient air filters. An optional charcoal filter also removes odors and some chemicals.

Dear Jim: I have been thinking about using either a UV or an ozone air purifier in my living room. I guess they both kill germs. Which type is better, how do they work and do they use much electricity? – Mike H.

Dear Mike: Both of them do kill microbes. A UV unit uses intense ultraviolet light inside the purifier chamber. Ozone models produce ozone gas which chemically reacts with the microbes to kill them.

Neither of them uses a huge amount of electricity. An ozone purifier will also help reduce other pollutants in the air by reacting with them.

The only drawback is some people are sensitive to low levels of ozone gas.

Write for (instantly download – www.dulley.com) Update Bulletin No. 861 – buyer’s guide of nine manufacturers (36 models) of window air conditioners, capacities, EER’s, airflow control, fan speeds, sizes, features, and a sizing worksheet. Please include $3 and a business-size SASE. James Dulley, 6906 Royalgreen Drive, Cincinnati, OH 45244.