Hot water, at 700-1300 psia, can be used in ejectors to provide facility exhaust capabilities similar to those achieved by the more familiar steam-ejector systems. In fact, such hotwater drives may make larger facilities feasible in some cases, because the size and capital cost of the hot-water accumulator should be considerably smaller, and the operating cost is roughly half as great. (However, it should be noted that, in most cases, a hot-water ejector needs a simple water separator.) Another advantage is greatly reduced noise. The pressure drop in the accumulator during a run is low and can be eliminated if desired. With a wind tunnel using an atmospheric-pressure inlet, a single-stage, single-nozzle ejector can provide for Mach 0-3 testing; efficiency can be improved by using two or more ejector nozzles aligned parallel for the supersonic part of this regime. Various existing and planned installations in Europe for Mach numbers up to 5 (and even 20 for a three-stage ejector) are mentioned.