I'm considering getting a "comfort pump" which will pump water from the hot line to the cold line under a sink so that there is no waiting for hot water, as well as saving the wasted water.
My concern is that the hot water is getting pushed back into the cold line and that will get fed into the reverse osmosis filter, and that the filtered drinking water will no longer be as good. I've seen numerous articles that state that contaminants from the hot water heater are not good to drink.
Then again, it might be just such a small amount of this water that gets into the RO filter, and the RO filter might do such a good job of eliminating contaminants that this problem won't be an issue.
I'm considering these 2 models of "comfort pumps":
- Watts 500800 Premier Hot Water Recirculation Pump, Blue
- Grundfos 595916 1/25 Horsepower Comfort Series Recirculator Pump
This question is related: Are hot water returns worth putting in?
I got this response from Watts:
The small amount of water from the hot water heater that may make it to the RO system will not matter. The RO does not allow water in constantly, only when pressure has been bled off the storage tank, as when the faucet has been opened, and if it does, the reverse osmosis system will reject the contaminants that may be present, mainly calcium and/or magnesium deposits, which could build up the water heater. The reverse osmosis system should not be a determining factor for installing a hot water recirculting pump, as it will have no effect.
I got this from the Hot Water Lobster. I'm skeptical of the claim that the powered pumps only last 18-24 months. I'm also skeptical of recirculating the water during the middle of the night.
On the other hand, when it's sunny where I live, I see no disadvantage circulating the hot water all day long, as my hot water tank would get unreasonably hot such that I had to add a thermostatic mixing valve.
The Hot Water Lobster Instant Hot Water Valve is thermostatically controlled and opens only when the hot water temperature at the HWL drops below the adjustable temperature setting (allowing thermal convection to slowly move the water through the system until it reaches your set temperature). With the Hot Water Lobster Instant Hot Water Valve, you should get hot water within 4-8 seconds at the faucet where the Hot Water Lobster Valve is installed. Powered pumps circulate the water at a faster rate than the thermal convection generated within your hot water tank. However, the speed the water circulates is indifferent to the user because hot water should always be available when you need it with the Hot Water Lobster Instant Hot Water Valve. Be aware that most pump systems: are restricted to timers or cycle buttons before the pumps will circulate the water. Which means hot water may not always be available during off times or at sinks without start buttons (when you may need it); during pump cycles, your entire cold water pipe is filled with hot water (as the water returns to your water heater), and because hot water is pumping for the entire time period, you cannot get cold water until after the pump stops. pumps often only last 18-24 months before replacement is necessary; initially the noise level of pumps is minimal but over time can become very noticeable (especially when your trying to sleep); pumps often cause electrical interference to televisions and radios; and installation is more complex requiring a nearby electrical source and electrical connections (to power the pump). On the other hand the Hot Water Lobster Instant hot Water Valve: incorporates the flexibility of an adjustable thermostatic control; is built with quality materials and workmanship for a long maintenance-free life, is easily installed (not requiring electrical wiring, timers or perishable pumps); and is completely silent. There are so many variables from plumbing system to plumbing system, calculating a standard energy saving formula would be difficult and very complex. In general, instead of replacing the water (wasted down your drain-while waiting for hot water) with cold ground temperature water (which has to be heated from a low temperature), the Hot Water Lobster Instant Hot Water Valve allows already warm water to circulate back to your hot water tank for reheating-which not only saves the cost of the water, water treatment charges (sewer charges), it also takes less energy to bring the already warmer water (being re-circulated) up to temperature. The more often hot water is used the more energy is saved (compared to not recirculating the water and heating ground temperature water instead). Pipe heat loss is minimal compared to the cost to heat 2-4 gallons of ground temperature water the 18-24 times a day (the average family uses hot water). And in cold months (when hot water is used 42% more often than in hot months) the heat loss is not wasted (any radiant heat provided by the hot pipes transfers to heat for your home). With or without a hot water recirculating system, the better insulated your pipes are the less energy is wasted.