Tankless Hot Water Heaters vs. Tank Type Hot Water Heaters
Tankless Hot Water Heaters vs. Tank Type Hot Water Heaters - A Product Review & Comparison
In the market for a tankless hot water heater? If you are, and you are not familiar with the operation of a tankless water heater, then
there are a few things you should think about before you make that purchase.
Hot water piping -- the basics
There are major differences between the way a tank type
water heater provides you with hot water, and the way the tankless unit does.
With a tank type hot water heater you turn on the faucet, and the hot water
begins traveling through the hot water pipe to your fixture. Since the pipe is
cold, it absorbs some of the heat, gradually warming up to the temperature of
This is why your hot water gradually goes from cold to hot
if you leave your hand under the running water. If your pipe run is very short,
the warm-up wonít be very gradual. The longer the pipes and the heavier the
piping material, the more gradual will be the warm-up since the pipe material
will be able to absorb more heat from the moving water.
Another factor in the warm-up is the speed at which the
water is flowing. The faster the water travels the faster the warm-up. This is
because the faster the water flows, the less time it is exposed to the cold
pipe. Obviously the ambient temperature is a major factor. If your pipes are in
the attic, and you are in Phoenix Arizona in mid summer, your pipes will already
be so hot they will absorb little if any heat from the water.
However, if you are in Truckee California in January, your
pipe warm-up will take far longer, be more gradual, and with very long
un-insulated pipes, the high temperature might never be reached due to the heat
loss from the pipes to the surrounding air.
Within a few seconds of the hot water reaching the fixture
the temperature stabilizes. Since you have a big tank full of hot water that is
pretty much at one temperature, the temperature at your faucet should not vary
much, even when you change the flow rate. A trickle of water is pretty much the
same temperature as with the faucet turned full-on.
Tankless hot water heaters
Now letís suppose you have a tankless hot water heater.
All of the previous warm-up factors apply plus a few more things come into
play. When you first turn on the water heater there is no big tank of hot
water to start flowing. There is instead a tankless water heater full of cold
water that immediately begins flowing into the hot water pipe. In order to heat
the water to full temperature, the incoming water must flow through the entire
heater since it takes time to heat the water. This will cause a longer delay in
getting the hot water to the fixture, and results in running more water down the
drain while waiting.
A simple way to picture the workings of a tankless water
heater is to picture a coil of copper tubing with a gas burner in the middle of
it. As the water travels through the tubing it absorbs heat from the flames and
gets hotter and hotter.
Outlet temperature depends on starting temperature and flow rate
The temperature of the water coming out of the tube depends on how fast the
water is flowing and what the starting temperature is. If you are starting
with 45 degree water, and the heater is capable of heating the water 90 degrees
at a flow of 1 gallon per minute, then you will get 135 degree water out.
But if for some reason the water temperature coming into the heater rises to 55
degrees, then outlet temperature will rise to 145 degrees. So be sure that
your heater is powerful enough to handle the maximum amount of flow you will
need, or you will see temperature fluctuations in the outlet temperature.
With electric tankless water heaters the water temperature is difficult to
hold constant with changes in flow rate. The electric heating elements
don't respond quickly enough to compensate rapidly for sudden changes in the
Turning on the tankless unit
To further complicate things, a tankless hot water heater
does not turn on until a sufficient flow rate is achieved. Most tankless water
heaters require between Ĺ gallon and ĺ gallons per minute to turn on.
So if you are in the habit of running the hot water tap
full blast to get the hot water to the sink, and then throttling it back while
you brush your teeth or wash your hands, then the tankless water heater will
change your behavior. When you throttle it back, the water heater shuts off,
and cold water is on its way. No more using just a trickle of hot water.
Hot water re-circ and circulating systems
Tankless water heaters wonít work with most hot water
circulating systems. If the circulating pump has enough power to turn on the
heater, it cause the water heater to run continuously until some safety
mechanism shuts it down, or your fixtures melt. Most donít have enough power to
turn the heater on and will just become cold water circulators.
Hot water demand systems
Demand type hot water pumps will however work with the
tankless heaters, and will get the hot water to the fixture more quickly and
without running any water down the drain. Two such pumps are the
pump and the Chilipepper CP6000. Unfortunately they donít solve the other
Tankless water heaters do have their place. They do
eliminate standby losses that tank type units have, the loss of heat through the
walls of the tank, and they do provide unlimited amounts of hot water.
your heater will heat the water to a high enough temperature at the flow rate
you desire and the lowest expected cold water inlet temperature.
Chilipepper Sales 1380 Greg St., # 221 Sparks Nevada, 89431