Good question Simon! We can recommend an installer in your local area, so please call us if you would like help in that regard. A licensed plumber for the installation, an electrician for the Transfer Switch and a B licensed plumber to sign off on installation, place a compliance label and submit paper work to AGA.
As for cost, this will depend on where the unit is to be located, how much plumbing is required, site access and travel costs incurred by the installer. On average we recommend you allow around $2,500.
You can find more information relating to Generac Gas installation here: INSTALLATION GUIDELINES and GENERAC GAS TRAIN INSTALLATION PROCEDURE