I have done several. The Guardian is metal not aluminum but will last past you. the 20Kw 83Amp On propane and 75? on Nat gas with load shedding would do whole shop. Put auto trans sw by
200Amp Panel .Make panel a subpanel .Tran sw becomes the serve disconnect.Unit weighs 580lbscould go outside .footprint is approx 27" x 48"
The Guardian series Generac 20kw and below have been using an all aluminum housing since they first came out with the Nexus controller and even the series before, the engine on these smaller units are air cooled V twins or an air cooled slant single cyl. as well as all aluminum the 20kw is only 451 pounds, the 25 kw and larger is an all steel casing but is not really that much more weight as the larger 1.5 liter inline 4 GM industrial engine (25-30kw) is all cast iron block and heads will make the housing being steel not much of a difference, the 45-60kws are using the industrial 2.4 quad 4 engine but again it is all cast iron I think I was told one time that the 25kw is about 700 pounds.
When you get into the quite source series which start at 22kw they are all water cooled and larger industrial cast iron engines using the 2.4 up to the 36kw and the 5.4 liter GM Vortec which is the generation III small block V-8 that GM uses in trucks and vans as the 4.8-5.3 liter but with cast iron heads not the aluminum that they use for the road vehicles on the 48kw, although Generac also uses the industral 4.2 Vortec which is the same V-6 used in many trucks and vans but again with cast iron heads but I have only seen them in the industral/comercial line Generac generators as well as a few Kohlers, Generac also used a few Toyota 4 cyl's and a couple other jap engines but these were older Generac's industral series now I think both Generac and Kohler favor the industral GM engines.
One thing you must do is find out what the calculated demand load is, us shooting from the hip on the size of the generator can be a big mistake because on a commercial shop you have no idea what they might have running like signs, electric heat, or other loads that might turn on when power is restored, all gas residential is one thing but a commercial business can be a very changing load and you might not know what they try to run, sometimes it can make sense to add a sub panel to just supply loads that they will need in a power outage and can save on the size of the generator allot.
