Speaking only of my home built equipment, I have no manufacturer's specs on the efficiency of my components. But there is undoubtedly a difference in all areas. 90% of the steam goes up the steam flue, so no more rain in the sap house. The hood encloses the flue section of the pan, and extends over the syrup section at a height of about 16-18" above the rim. The hood is about 24" high above the rim. The steam exits through an 8" duct through the roof. The preheater has 10 - 80" cooper loops (40" down, 40" back) through the flue section of the hood. My feed tank is about 6" higher than the preheater outlet. Sap enters the preheater at the outdoor temp, which is usually around 40 degrees, and exits at 100 to 150 degrees higher (I got different readings when I checked it). There is definitely some steam coming out of the float valve. With such heated sap entering the flue pan, there is not a very noticeable diminishment of the boil at the entrance point.
So, you will see an increase. How much depends on the equipment and your firing technique.
Gary / Zena Crossroads / 42˚ 00' 24" N / Hobby in Early '70s, Addiction since 2014
175+ taps on 3/16 (60 of which are on two Lunchbox Vac/Releasers)
12x34 timber framed sap house w/attached 10x34 shed roof for storage
2 x 6 Smoky Lake hybrid pan on Corsair arch with AUF/steam hood/preheater/concentric exhaust
7.0 KW Sun Power PV System, Smokey Lake Filter Press/Steam Bottler, Modified NGMP RO - 2 4x40 posts 200 gph