Per usual Sophie is right. After years of having ours side by side, we just bought a bracket and stacked them. LG front loaders.

Have you settled on what you would get as a replacement washer? If you are looking at current Whirlpool/Maytag front load models, your existing stacking kit may fit the new washer or a current stacking kit may fit the existing dryer. That was the case a couple of years ago when I helped a friend replace the dryer in her Whirlpool duet stack. (In her case, it was the dryer she wanted to replace, but it seemed that new kits fit older machines and vice versa.) As tjmwine says, delivery companies generally refuse to stack different brands or mismatched sets. So, you may need help in putting the old dryer back up. That said, if you have basic DIY skills, or have friends who do, and you buy a different brand of washer with dimensions similar to your old Duet, you may be able to adapt the new washer's stacking kit to work with your existing dryer. This generally involves drilling new mounting slots or holes in the old dryer's sheet metal so the bracket can tie on with sheet metal screws. In past threads here on the subject of stacking mixed brands of washer and dryer, a common suggestion has been to add a platform of 5/8" or 3/4" plywood an inch or so above the washer and place the dryer on that. (Hopefully, your dryer vent still lines up properly.) Others here have gone with variations on what Dan1888 suggested above --- putting a pad or pads on top of the washer. That gets frowned on in areas that are earthquake prone (and some that are not) , and you'll sometimes see recommendations for adding a retaining bar or two across the front of the dryer to limit the risk of it falling forward from a laundry closet.

I saw an ad in the local nextdoor marketplace. Someone bought a home in one of our upscale neighborhoods and bought a brand new Washer and Dryer, so they were selling the Speed Queen set for $100.00 that came with the house. Knowing that my Amana washer and dryer were built in 1995 and are close to the end of their useful life, I jumped on buying a used set by Speed Queen that was built prior to their redesign disaster. The old Maytag, Speed Queen and Amana w/d were work horses. Whirlpool bought out Maytag, Amana, Jenn-Air, and KitchenAid and the quality is not what it once was. Newer machines just don't have the longevity of the old machines and the efficiency standards have reduced the cleaning quality. I expect I will get another 20 years from the used Speed Queens.

I have a Washtower and am very happy with it; I've only had it about 9 months (replaced a horrible Samsung pair), but I expect at least 11-12 years from it. " apparently replacing perfectly usable ones " "apparently" is carrying a lot of weight there. Also, usable doesn't mean effective or efficient. You keep missing the other benefits, like the fact that they use less water and energy , and that they require less power to dry the clothes (and clothes dryers are power hogs). And the benefit of not having to replace clothes damaged in top load machines. Why are you working so hard to convince this poster that she shouldn't get a front load washer? They're better by every measure, unless maybe if you have a baby and need to dump dirty cloth diapers into the tub (then a top loader could be more convenient to use).