Mounted mine vertically - battery terminals up so air flows up and out. Lots of air around it. Doesn't get very hot as others have noted. Fans come on maybe a few times an hour for maybe a minute (Florida sun). Not very efficient, I am getting maybe half the panel output (where same bank gave me almost panel ratings with Victron MPPT). Still, I have averaged about $4.00 a week at $.20 a KWH so far at 1000 watts of solar (in central Florida). Since I have way more panels than I need for my battery bank and inverters I think another one of these is in my future. Nice when hooked to metered shore power. Oh - I tried it with the generator and it did actually work and lightened the load during the day. Still, it is only half as efficient as a good MPPT controller so keep that in mind.