Let’s run down the list of water heating methods for residential water heaters, and let’s also leave out the more exotic methods or perhaps just touch on them lightly. We shall examine solar first.
As you can tell from the title water heating can be a fairly broad topic. I didn’t list all of the methods being used for residential or light commercial water heating. Add to the list geothermal, electric, natural gas, propane, oil fired, wood stove, boiler, and there is no shortage of people working on other experimental water heaters.
Solar Water Heating
Solar water heating systems can be a great bargain, providing very low cost or even free hot water, or on the other hand they can be some of the most expensive. Solar water heaters come in two basic flavors, passive and active.
Passive solar systems do not have a pump. They just sit there and do their thing with no human interference needed. Active solar systems utilize pumps, valves, and controllers and are much more efficient and expensive than passive solar systems. They also break down more often and can be pricey to maintain.
Solar water heating is very location dependent. If you are in an area where it never or rarely freezes, with no hard freezes, then a passive system is an option. There are several kinds of passive systems. There are batch systems, which basically consist of a tank of water in a miniature green house.
Another passive system uses solar collectors mounted lower than the tank so that as the water heats up it naturally rises into the tank. There are of course many variations of the passive type systems, collectors in series, in parallel, with and without storage tanks, back up resistance heating etc.
If you live where freezing is a problem then you need an active system of which there are many variations. Some heat the water directly, some use an anti-freeze solution in the collectors, some drain the water out of the system when it approaches freezing etc.
If you live where freezing is not a problem and there is an abundance of sunshine then you might want to seriously look into solar water heating for your home. The fuel is free.
Storage Water Heating
Good old fashioned tank type storage water heaters are my favorite and preferred choice. Why? Well, for one thing I am lazy. I just want hot water from the faucet when I turn it on, or at least as quickly as I can get it. I don’t want to deal with breakdowns, and I do not want to go without my morning shower. I don’t want a remote control for the water heater as many tankless heaters have.
Can you imagine what it’s like when your plumber says the part is on order and they will have it in a week or so? It would make my day. This can happen with tankless, solar, and other exotic water heating systems.
With a tank type water heater the first thing that usually goes bad is the tank begins to leak. This produces a puddle under the water heater giving you plenty of advance warning that you need to replace it. That way you don’t miss any showers. If something does go wrong with your natural gas or electric storage water heater just about anyone in town can fix it in an hour.
As for speed, the storage water heater is loaded with hot water so when you turn on the tap hot water is on its way. Not so with a tankless water heater. It has to first heat the water, and the first water leaving the outlet is cold. The water needs to pass through the heat exchanger to become hot. This means tankless water heaters on average take 10 to 20 seconds longer to get hot water to the fixture than a conventional storage water heater.
Heat Pump Water Heaters
Heat pump water heaters are a very efficient method of heating water as long as it’s not too cold outside. Heat pump water heaters don’t have to generate heat like electric water heaters, they just move it from one place to another which is much cheaper than creating the heat.
They work just like your air conditioner. There is a heat exchanger inside the tank that heats the water and a heat exchanger outside that sucks the heat out of the outside air. The only real catch is there must be some heat in the air to move.
Heat pump water heaters take quite a bit longer to heat water than electric resistance heaters or gas water heaters. They get slower as the water temperature increases and or the outside air temperature decreases.
The initial cost is of course fairly high compared to a storage gas or electric water heater. There are variations like for instance the ground source heat pump which circulates water through pipes under the ground to obtain the heat.
Heat pump water heaters need backup resistance heating for those times when the outside temperature drops too low for the heat pump to work effectively.
Tankless Water Heaters
Tankless water heaters are very popular these days, presumably because they are a green plumbing product that reduces the amount of energy you use to heat your hot water. While it’s true that tankless water heaters do not have the standby losses inherent with tank type water heaters, the savings isn’t all that much. A tankless unit probably saves you about $5.00 a month.
Most tankless water heaters are gas types because in order to heat water rapidly with an electric heater the current draw needs to be so high that normal house wiring isn’t heavy enough and you will need to run heavy wiring with big circuit breakers and may even have to have the electrical service to you home upgraded by the utility company. As you might imagine it can get pretty expensive.
Gas tankless water heaters need larger venting than storage heaters, and often it needs to be stainless steel which is pricy. They also need a larger gas line than gas tank type heaters. When the power goes out most tankless water heaters will not operate.
Tankless water heaters have a minimum flow rate. If you draw less than the minimum the heater shuts off, and several seconds later… surprise! Cold hot water from the faucet! This means you probably won’t be able to run a trickle of hot water for anything anymore. Not good for water conservation.
If you want endless hot water, or just run out often, then the tankless hot water heaters could be right for you. You won’t ever run out of hot water, and it is a little cheaper to heat the water. The best piece of advice I can give you if you are going to install a tankless water heater is make sure the installation is done properly.
Improper installation can cause a lot of headaches down the road, so make sure the installer is trained on the type of unit you are having installed.
Point-of-Use Water Heating
Point of use water heating is used to describe several scenarios. There are water heaters, both storage and tankless, that are very small and can be used to supply hot water for small uses and hand washing, but not large enough to say take a shower.
If a large water heater is very close to the fixture then it too is a point-of-use water heater even though it may be large enough to serve the whole house.
Point of use water heating is the most efficient as far as the hot water distribution system goes. You never wastefully run water down the sink waiting for it to get hot because the piping is so short. You save plenty of water with such an arrangement. You save time since you don’t have to wait long for the hot water to arrive. Point of use plumbing is a good green method of plumbing a home.
Homes can be designed with bathrooms and kitchens located so that a single water heater can serve several locations and still be called a point of use system.
One can combine some of these water heating methods to save more water and energy making them even greener. For instance, it’s possible to use both a tankless water heater and a solar water heater. You never run out of hot water and when the sun shines your hot water is much cheaper. When combining systems you should always check with the manufacturers first to make sure the combined systems are compatible with each other.