Six Advantages And Three Disadvantages Of Instant Hot Water Heaters

by Nicola Temple on May 31, 2012

Instant hot water heaters are more commonly known as tankless hot water heaters, but they can also be known as continuous flow, on-demand, and point-of-use water heaters.

What these water heaters all have in common is that they instantly heat water as it flows through the device and they don’t store water.  This style of water heater has a number of advantages that help the planet as well as your bank account and I promise I explain these later.

In the meantime, it’s probably worthwhile explaining some of the different styles and options available in terms of instant hot water heaters.

Central versus point-of-use: You can either get central tankless water heaters that are used to provide all hot water throughout the house, or you can get smaller point-of-use (POU) versions that are associated with a particular fixture or room, such as a shower or bathroom.

instant hot water heaters

Point-of-use instant hot water heaters can truly deliver instant hot water as they cut down the distance that the water travels from the point where it’s heated to the point where it’s used.

The obvious advantage of having several POU units is that the water has very little distance to travel between where it is heated and where it is used. This improves efficiency and provides the “instant” aspect of instant hot water heating. The disadvantage is that you have to buy and maintain more units.  Some home owners resolve this by using a central tankless water heater and then putting in a POU unit at a fixture that is far from the central system if necessary.

Full on/full off versus modulated: The names are rather self-explanatory. The full on/full off tankless hot water heaters are just that – the heating system is either on or off and there’s no in-between. The temperature of the water is basically controlled by how fast the water flows through the system. The slower the flow, the less volume there is to heat and the hotter it is.

Modulated versions change their heat output in response to the flow rate much like a dimmer switch. If only a little water is needed then the heating unit operates at a lower setting.

Combination boiler: Some tankless hot water heaters can also serve as a central heating system and these are known as combination or combi- boilers.  This means that you have your air and water heating looked after in one box.

Six advantages of instant hot water heaters:

  1. They can save you money in the long term: Tankless water heaters use no energy when they’re not in use, so when you’re at work, asleep or on holiday, there’s no energy being used to heat a tank of water nobody is using. This can translate to some long term cost savings. Switching to a tankless water heater can cut water heating expenses by 30%, which for an average family could be more than $100/year on gas bills.
  2. They are more energy efficient: This is a big bonus for the environment as well as your bank account.  A conventional tank-style hot water heater has an efficiency of around 60-65%. This means that for every dollar worth of gas you put in to heating your water, about 35-40 cents is wasted…literally, flying out the window. Tankless hot water heaters have an efficiency of anywhere from 85 to 97%. This means far less of the money you put into heating your water is wasted.
  3. You will never have a cold shower again:  We’ve all been there once in our lives. The holidays where the house is full of guests and you’re the last one in the shower and there’s no more hot water. It’s miserable. Tankless hot water heaters, however, heat on demand and match the water production requirements. There’s no tank to drain! You will never run out of hot water and nor are you heating a whole bunch of water you don’t need.
  4. They take up less space: Let’s face it, hot water tanks are ugly and take up space. Tankless versions are slim and space saving, though I suppose the cat would have to find a new place to nap.
  5. They have a longer life expectancy: Tankless versions often come with 10-20 year warranties because they have a longer life expectancy than conventional tank-style water heaters.
  6. There’s no risk of water damage: There’s always the risk of water tank failure or rupture, and Murphy’s Law says it will almost always happens when you’re away or when you’re house is filled with guests and you’re about to serve the main course. With instant hot water heaters there is no water storage and therefore no risk of water damage.

Three disadvantages of instant hot water heaters:

  1. You pay a little more for instant: Tankless-style hot water heaters are more expensive initially and so it’s important to weigh the long term savings with this initial short term cost. For example, a natural gas water heater tank by Rheem  costs about $355 whereas their indoor direct condensing tankless water heater runs around $1190.
  2. There can be a delay in getting hot water: Sometimes, the ‘instant’ is lost in the pipes between the instant hot water heater and the tap. Depending on how far the tap is from the central tankless water heater, there could be quite a delay before you get hot water out. This is because all the water that’s been sitting in the pipe at room temperature has to be cleared out first. Of course, this is also true of tank-style systems. A large delay at a particular source can be resolved by installing a smaller POU tankless system near the fixture.
  3. Tankless models are less flexible in terms of heat source: Essentially all tankless models use either gas or electricity as their heat source and most modern models use natural gas or propane. This can be a little limiting as storage tank versions can make use of geothermal heating and other eco friendly heating options. The exception is that solar water heating can be used in conjunction with tankless water heaters.

What are the most efficient whole home tankless hot water heaters?

The heaters are scored on an Energy Factor (EF), which is the ration of energy in to the energy out. In other words, the amount of gas put in to the system that is converted into hot water; the higher the EF, the more efficient the water heater. To qualify for Energy Star, the heater must have an EF of 0.82 or more.

So, the top three brands and models that are currently available on the market are:

#1 – Bradford White Corporation, which makes both gas (TGHE-160E-N and TGHE-160I-N) and propane (TGHE-160E-X and TGHE-160I-X) models with an EF of 0.96.

#2 – Bosch Therm, which makes a gas model (C 1050 ES) with an EF of 0.94.

#3 – Intellihot makes a gas model (eNG200i ) with an EF of 0.93.

The advantages of instant hot water heaters certainly outweigh the disadvantages. The challenge can lie in making them fit with existing systems. This makes converting to a tankless style water heater a really good option for new builds, major renovations or replacing existing gas heated tank-style versions. The video below from Tom & Larry’s Excellent Home Energy Savings talks a little more about the advantages of these hot water heaters.

{ 1 comment… read it below or add one }

Heather June 1, 2012 at 10:05 pm

We needed a new hot water heater recently and looked into tankless, but it turned out that our power supply was insufficient and we would have needed to replace a lot of wiring and the circuit breaker box in order to accommodate it. Too large an expense :(


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