Solar Hot Water and a Tankless
To really reduce your hot water heating charges you could look at adding an active solar water heater in conjunction with a tankless water heater. The rays from the sun would pre-heat the incoming water and then the tankless would simply finish the job. It’s difficult to get a solar water heater to produce water hot enough for today’s household demands, but with the technology in a tankless system it’s a perfect fit. Tankless water heaters are smart no, they check incoming water temperature and vary their burners to adapt. So if you have relatively hot water coming in to a tankless it will scale down its natural gas injection to ensure that water out temperature is at your set level. If the burner is scaled down so is your gas bill as only a fraction of fuel is needed.
This is a complicated system and it will be costly, if you are doing this to save money you probably won’t see a breakeven point for a long time. If you’re interested and looking at installing a Frankenstein system you are probable doing it for the environment.
If your installing somewhere in the southern states this will be a lot easier as you don’t have to worry about sub-zero temperatures. Up here in Ontario it’s a definite issue and there are a few systems that can be installed. There is the Active Glycol-based system that circulates food grade glycol and transfers the heat via a heat exchanger to the potable water; this is less efficient but the safest and most popular system in Ontario. The other way is though a drain back system, potable water is forced though the solar collector and drains instantly when the water is shut off. Both these systems work to preheat a tankless systems incoming water supply ultimately reducing the heat and gas needed to raise water temperature to the desired warmth.
These dual systems are not very popular due to the increased expense but a tankless is well suited and designed for a hybrid system. If the idea seems interesting but the price too high you should note that they can be installed in stages, tankless first and then the flat plate solar collector.