Sliders as a style of window have a higher air infiltration and water penetration rating than double hungs as a style.

The large unsupported span of the middle of a slider window usually equals lower Design Pressures and higher Air Infiltration as Sky describes.

Single/Double Hungs have support on both sides and therefore are tighter and more resistant to water and air infiltration.

Sizing is also important in your consideration. Normally sliding windows are wider than they are tall and double hungs taller than they are wide. In other words, if you have 5040s and 6040s you will have to convert those to 2 - 2640s mulled or put together and 2- 3040s. If these are in your bedrooms and you do not a door to the outside, you have to stay with the sliders, go to casements of the same size, or change the opening and use larger double hungs to satisfy the fire or egress code. The smallest double hung in most cases to meet the egress code is a 3050. These are all things you should discuss with your window supplier but at least be aware of them. Good luck!

I am trying to decide on whether to replace my old aluminum single pane windows with either sliding windows or single hung...the sliding windows seem to be cheaper...is it because of the higher potential for air/water infiltration mentioned in the other posts?

a good part of the reason, sliders are not sold anywhere near as often and the technology has not advanced near as much so they are still using mostly older profiles and style parts for which the cost is not as high.

If cost was not an issue and you want the best performance in an opening designed for a slider (usually larger horizontally than vertically) I go with a casement window. They seal tighter than any other operable window. Plus, I think they look much better and they are easier to clean since most slider windows don't tilt in and you have to physically lift them out of their tracks and set them on the floor for cleaning.

ick... casement windows are such a pain, I've had them in 2 homes and finally replaced them all in current coatal small home. Everythng is expensive and diffficult to repair and fix with casements ex hinges and weather stripping, not to mention the screens are on the inside which no one in the South will tolerate year round. The interior crank handles get in the way of all window treatments. They are leaky windows. Once they have been painted once the weather stripping is gone because it is hard to convince painters not to paint the bulb type weather stripping .... very out of date window style ...unless you live in New England and can keep your windows open half the year ...

What are you trying to say Robbie? This is a 4 year old thread.