People simply don't use enough antifreeze or do not winterize properly. You never try to add AF to a hot water heater. There is NO WAY you can do it without enough dilution to cause a freeze up.. Every year folks try this instead of draining and bypassing......... D'oh.....

Spring Count:

1 HX
4 Valves (both plastic and brass)
1 Copper Manifold
1 Water Heater

And I think the coldest we saw was about -14F.... It was not extreme cold, but long stretches well below 20F....