Dear Jim: I need to upgrade my old wood windows, but I like how the frames look. They don’t stay open now and the single-pane glass is not efficient. How can I switch to double-pane glass and tighten them up? – Brad J.

Dear Brad: Switching to double-pane glass, or even triple-pane glass in severely cold climates, is the best way to improve the efficiency of your windows. The new types of glass with efficient coating will also reduce the fading of your curtains and furniture and reduce wintertime condensation.

The best method to switch to more efficient glass and more airtight windows is to replace them with entirely new wood windows. Unless the styling of your existing wood frames is extremely unique, you should be able to find new ones with somewhat similar frames. It is also possible to get new custom-designed frames, but they will be expensive.

Another, almost as efficient, option is to install replacement double-pane sash kits in your existing window frames. These kits are basically new replacement windows without a new frame. Before selecting this option, be sure your existing window frames are in good condition.

Sash replacement kits are only somewhat less expensive than totally new replacement windows because the sashes are the most expensive parts. You will realize an overall lower cost because installing these kits is a fairly easy do-it-yourself job and you will save the labor costs.

Another advantage of installing sash kits is they are designed to operate like replacement tilt-in double-hung windows. This makes cleaning the windows an easy task from indoors. Each sash will tilt in independently so you have access to each side.

Your old wood windows likely have window weights inside the window frame. These weights counterbalance the weight of the sash to hold it open.

Since your windows don’t stay open now, the ropes connecting the weights to the sashes are broken. The sash replacement kits include new frame channels which will hold the sash open in any position.

Most of the major wood window manufacturers offer tilt-in sash replacement kits. They are available in many sizes in 1- or 2-inch increments, so they fit almost any older window frame. A typical kit includes the new efficient sashes, tilt-in pivots for each sash, jamb liners, locks, and all the required hardware.

You will need just a hammer, putty knife, pliers, and saw.

To install a kit, pry off the old sash stops and remove the old sashes. Remove the window weights and fill the holes with insulation. Using the fasteners provided, attach jamb liner clips in the frame and snap the liners in place. Insert the upper sash first, then the tilt-in pivots followed by the lower sash.

The following companies offer window sash replacement kits: Jeld-Wen, (800) 535-3936, www.jeldwen.com; Kolbe & Kolbe, (715) 842-5666, www.kolbe-kolbe.com; Marvin Windows, (888) 537-7828, www.

marvin.com; Vetter Windows, (800) 838-8372, www.vetterwindows.com; and Weathershield, (800) 222-2995, www.weathershield.com). Send inquiries to James Dulley, 6906 Royalgreen Drive, Cincinnati, OH 45244 or visit www.dulley.com.

Dear Jim: During the summer, my central air conditioner did not keep the house cool enough on hot days. Why does it cool fine on some days and at night, but not on the hottest afternoons? – Karyl M.

Dear Karyl: Air conditioners work by pulling heat from inside the house and exhausting it outdoors through the condenser coils. When the outdoor air is hotter, it is more difficult to transfer heat, so the efficiency and cooling output are lower.

Also, when it is hottest outdoors, more heat is being transferred into your home through the walls, windows, roof, and air leaks. When you combine reduced cooling output with this, you experience your problem.