> What I haven't been able to find an answer to is that everybody says heat pumps need low delta T of 5-10 degree F (implying high flow rate for given heat tran

> What I haven't been able to find an answer to is that everybody says heat pumps need low delta T of 5-10 degree F (implying high flow rate for given heat transfer) I don’t see why this would matter at all. Maybe the heat exchanger would need to be sized differently for a different flow rate, but in general a lower entering water temperature on the hot side seems preferable.