Has anyone had any experience with side arm heat exchangers for water heaters. I have a new Garn wood boiler (I LOVE IT) and have installed a side arm heat exchanger on the side of my 80 gal. electric water heater. I have connected the primary supply from my Garn to the top of the side arm heat exchanger. It only will get the top 30 to 40 gallons of water in the tank hot. It also has a very slow recovery time. Can anyone give suggestions for quicker recovery.