Our Sunamp iPV (with PV obviously) as pre-heat worked superbly when we had the Combi. The Sunamp was handling 95% of our hot water from April to Sept months and about 5% during the least sunny months of Dec to Jan. Our Sunamp iPV has a mixer valve on the output limiting the flow temp to 45C; still plenty hot enough for all our HW uses.
During the very sunniest weeks of the year we simply turned off the combi bolier completely and let the Sunamp handle 100% of the DHW duties.
The flow rate from the Sunamp is at mains water pressure that there is no loss of pressure when someone is using hot water tap at the same time as someone else having a shower.
NB I am not referring to using the Sunamp to store heat FROM a gas boiler, but rather the opposite to avoid using gas altogether (or as much as possible).
Cylinders are cheaper and it you don’t need the space saving feature of the Sunamp then more often than not a cylinder will be the natural choice.
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