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Please excuse my ignorance - we want to buy a typical slanted rooftop solar water heater for our home. We thought 200L would be an acceptable capacity, but the vendor we visited today said that we should have 300L or more. When I explained that we had calculated our hot water needs and 200L was more than sufficient, he countered that having a larger capacity tank would mean better water pressure at the shower head.

Now I'm no physicist, but I was under the impression that flow rate for these tanks depended on two things: vertical distance from the outlet (letting gravity speed the rate) and pipe diameter. Is there a significant difference in flow rate simply due to tank size?

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up vote 0 down vote accepted

No, unless the larger tank is taller, increasing the average height.

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