solar heat can be used to assist your domestic hot water heating if using a tank. the water going into your conventional water heater can be preheated in another tank by the solar collectors. the biggest energy use is heating from water source temperature to the desired use temperature.
if the solar heater water is hot then your conventional heater may not come on at all; your heater has to have a thermal mixing valve and make sure the water leaving the tank isn’t hotter than your set temperature.
the tankless heaters save on not wasting heat during storage, a lesser amount of heat used. the far greater amount is changing the temperature, not maintaining it.
Water takes a lot longer to heat up at the faucet – I think this is because the water in the tank is also heating the pipe
No electricity means no hot water, even with gas tankless heaters
Tankless water heaters turn off if there’s not enough flow
With (4), if you’re using hot water (rinsing dishes, taking a shower), but don’t keep the flow high enough, it can turn off the heater. So, unbeknownst to you, there’s cold water coming up from the tankless heater while you’re showering – water turns cold and you have to stand there shivering while you wait for the hot water to show up again (after increasing the flow).
We are tankless, and there’s definitely a learning curve.
We’re remodeling our home right now and this was one of the areas we looked at, since our existing tank heater is getting pretty old. I read the information at energy.gov and talked to the master plumber on our project and, between them, was convinced we would never see any significant economic return from buying a tankless heater.
I decided about ten years ago that the next time I needed to replace my tank I was going tankless. However…
-the house we were living in at the time was in a bad school system, so we decided to move. Around the same time we realized that our existing water tank was already nearly 20 years old and would have been a major sticking point for any potential buyers, so we replaced it. No way I was going to pay a premium for tankless when I wasn’t going to get the benefit of it, so we opted for another tank.
-in our current house we’re about 2-3 years away from replacing the tank, but about a year ago something occurred to me- right now the only items in our house that use gas are the water heater and the dryer, and our gas bill is about $25/month. I could put in a tankless unit for maybe $3,000-4,000, or probably under $1,000 for a new tank. What would I save each month- $5? $10? I already spend so little on gas that there’s no way I’d ever recoup the extra cost of a tankless unit.
Your scenario is not in any possible way related to the one I described. In this case, your friends are choosing the components…and paying the difference.
What “scenario” did you actually describe? ISTM you just assumed that there was some small energy efficiency and explained why such a small efficiency wouldn’t generally be opted for. However, there are plenty of other obstacles and the greater efficiency can’t really be assumed in all cases.
tankless can’t keep working ? thats the tank ones, they run out.
Tankless has to be a bit more complicated to get the temperature stable. without the complicated mechanisms, the flow or temperature would change too much. Also the wiring has to be upgraded to delivere huge power to heat up a proper flow.
But tankless is no good for solar hot water or heat pump water
heat pump hot water is where the air or ground as heat source. These work like reverse cycle air con or refridgerator… The cold side is the outside or the ground… the hot side is used to heat the water.