The system is already set up with a shut of valve in place would be the case of unscrewing a couple of double unions not really a huge task 
Having a back up is a good idea in the event of an actual heater malfunction, but won’t be of benefit if the power supply is compromised.Wouldn't there also be the problem of using a singular heater that it fails to heat the water?
Is it not a dome thing adding a spare to kick in if that happens
I Suppose there designed for pond volumes not many people have 3000ltrs of water sat in there home.Saying “pond heater” is akin to saying “aquarium salt”. It’s a heater. What you need for larger volumes is the appropriate wattage, and appropriately placed so that water flow disperses the heat generated evenly thru your system. The design is really only relevant to the aesthetics of what your specific set up is geared towards![]()
Dude the plumbing is in just a thought I could add an inline with little time yeah the build has already been costly and I'm hoping my first time plumbing worksMy “submersible” sits in my sump directly in the flow of all the water that circulates through my system. I honestly cannot see how having an inline would be any more efficient.
Even time you have to cut hard pipe and put a union or shut off inline you are greatly increasing cost and adding potential fail points to your set up.
At the end of the day it’s your project, your money, and your call 100%
Likejjohnwm said, some folks like it more techy, if that’s your jam, have at it brutha. No judgment here
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