CapeCoaler wrote:But if your GPM of DHW exceeds the rated
capacity of the indirect it will eventually get cooler...
Tank size gets you 'first hour rating' greater than your 'next hours' rating...
Because of storage...
So a bigger tank works for short duration high flow events...
Most normal residential indirect tanks take 150k-175k inputs...
Most are not installed to maximize the input...
RTFM...
That was my point. A steady 6 gpm draw takes over 200k BTU's to maintain. The heat exchanger in my indirect can't support that even with the boiler water at 200 degrees and the piping/circulator ideally sized. With that said, that kind of load just doesn't happen in a normal 2 bath house, at least not for very long. I agree with Scott that if the indirect is reasonably sized for the house, you will have all the hot water you want. I have a family of 4, and several times per year my inlaws stay with us for a few days. 4 back to back showers, bath for the kids, laundry, dishwasher, etc - no issues.
The indirect in my dad's house is much smaller than mine, but is piped with 1" copper and a serious Grundfos circulator. It did not perform well with the the oil boiler setup as "cold start", but does very well as long as there are some BTU's to pull out of the boiler when it needs it.
