My reasoning would be... Heat rises, so rather than responding to the temperature of the entire water volume (as it would in the horizontal position,) in the vertical position, the sensor would be fooled by the warmed water coming up from the element and prematurely turn-off. It would probably cycle on/off much more often - never efficiently heating the water and possibly wearing out the heater switch more quickly. My 2 cents worth, Rick -----Original Message----- From: gsas-member-bounces@thekrib.com [mailto:gsas-member-bounces@thekrib.com] On Behalf Of Shango Los Sent: Thursday, August 09, 2007 6:43 PM To: 'Greater Seattle Aquarium Society member chat' Subject: [GSAS-Member] Heater Goes Where Hi all, I have always learned that the heater in a 30 gallon should go horizontal about 3 inches above the bottom of the tank. I have a tank set up where that location is less than optimum. I would like to move it to vertical about 5 inches from the wall on the opposite side of the tank from the filter. Seems to me there shouldn't be much difference. Is there any sage reason why the heater should really stay horizontal 3 inches off the bottom? Thanks Shango ________________________________________________________ Shango Los Phone: 206-595-9006 Fax: 206-729-5271 www.ShangoLos.com www.SunbreakShines.com _______________________________________________ GSAS-Member mailing list GSAS-Member@thekrib.com http://lists.thekrib.com/mailman/listinfo/gsas-member _______________________________________________ GSAS-Member mailing list GSAS-Member@thekrib.com http://lists.thekrib.com/mailman/listinfo/gsas-member