Hmm, Toilet water that has been standing in the tank for more than 1
hour is warmer, in most all cases, than the cold water inlet. Inside
air temps are almost always warmer than ground water temps, so the water
in the tank is slowly heating up as it sits there.

This is an argument for the balanced flow model in GFX. That is, hook
GFX output to cold water supply EVERYWHERE, in EVERY sink, EVERY
toilet. This optimizes heat recovery from the waste water.

There is an exception to this rule however. In areas that have average
ground water temps of 60 degrees or above, the sinks and perhaps washing
machines will not get GFX heated water. Even dishwasher supply can be
GFX connected. This can be retrofitted in a house with a basement as
you only need to separate sink and washing machine supply lines from the
main supply and route them to a new feed line that originates on the
cold side of the GFX.

Canada and the US states that border Canada can easily heat EVERYTHING
as average year round ground water temps are at least 15F or more lower
than US Gulf Coast states water supplies.

This GREATLY simplifies the hookup and significantly increases the heat
recovery of the unit when there is a balanced flow rate, i.e. fresh
water in == waste water out. The closer we come to that ideal, the
better the efficiency of the unit.