I use 11" Flexwatt that's rated at 20 watts per foot on my 41 quart tubs that are on my quarantine rack that are set up for belly heat. The strip itself is a foot long (measures eleven inches wide by twelve inches long) that's run with a Helix thermostat. The tub sits on the 11" portion of the Flexwatt and with the tstat set to 95, it keeps the warm side 90 to 91 degrees with the room temp set to 78 degrees on the baseboard heaters. Works fine...never had a complaint from any of the tenants, lol!