Hot water goes cold in the pipes: what to do
This is a common problem in most houses I guess, but some are worse than others. Anyway, having just moved into a house that is on rainwater, I'm interested in finding a solution for the water that is wasted when you run the cold stuff out of the hot pipes if it hasn't been used for awhile. At this time of the year it goes cold quick. We have one bathroom that is a fair distance from the heater and it takes at least one basin-full of water to get any hot through.
There are 3 options to pursue. The first is lagging. This is OK as a short term solution - it keeps the water in the pipes hot longer but it will eventually go cold. So it's fine in the kitchen, where you might want hot water periodically over a fairly short space of time. There's still the sink-full you lose the first time you turn on the hot tap.
The second option is the circulation pump idea. We tried this once at a house that had a twin element, with the top one on standard rate. We found that energy costs went way up because the cooler water being returned to the heater caused the top element to come on all the time. When we disabled the top element, we were running out of hot water because the circulation of water through the system was creating a lot of heat loss on the round trip and so the overall temp in the cylinder dropped, and because it was on off-peak, it wasn't heating up again. This solution saves water but costs more to run. You also have the overhead of the circulation pump.
The third is the thermostatic valve, which diverts the cold water to somewhere else until it reaches a preset temp. You can either store it in a bladder tank to be reused next time you turn on the cold tap, or you can divert it to your rainwater tank. Probably the only downside to this one is that you turn on the hot tap and nothing happens for awhile. They tell me you get used to it, but I can imagine visitors washing their hands, only to find no water coming out. So what do they do? Turn the tap more... and more... and then out it comes like Niagra Falls and hot water all over their nice clean frock.
I have been wondering if a combination of all three would work. Say you had one of the thermo valves in the hotwater line near it's farthest point, with the cold water return piped back to the hot water cylinder. You set the temp so that it's a fair bit below normal hot temp. As the water in the pipes cools, the thermostat opens and the water circulates back to the cylinder. When the hot reaches the thermostat, it closes the divert valve again. Sort of similar to the circulation pump but it only happens periodically. Rather than trying to keep the water in the pipes at normal temp, it keeps it a bit cooler, but not cold. There's less time to wait for warm water to come through because it's already part way there. Lagging helps to keep it warmer. Then maybe a thermo valve set up on the kitchen sink and the vanities.
The valves are about $130 each. To install one in the line on the upstream side of a tap, you also need a diaphragm valve which enables the setup to work when the pressure drops (when a hot tap is turned on downstream). Don't know how much they are, but I'd guess around the same amount.
So, does anyone have any experience to contribute?
