what is the downside of a tankless water heater? (pros and cons)

what is the downside of a tankless water heater?

Instant water heaters, also known as on-demand or instantaneous water heaters, have many advantages over traditional instant water heaters and can be a good long-term investment.

However, like other products, they have drawbacks and are not suitable solutions for all homes.

Unlike traditional water heaters, which continuously use energy to maintain the water supply, tankless water heaters consume energy only when the water heater is turned on or when appliances are used.

This on-demand investment style leads to the greatest assets. Energy and cost savings.

In addition to saving energy and costs, there are many other reasons to choose a tankless water heater compared to traditional water heaters. Instant water heaters produce an infinite supply of hot water, take up less space, have a lower risk of leaks, are safer, and have a significantly longer life expectancy.

The main drawback of instant water heaters is that they are significantly more expensive to acquire (units and installation) than instant water heaters. On average, instant water heaters, including installation, cost three times as much as instant water heaters.

In addition to the high acquisition cost, instant water heaters have many other drawbacks compared to instant water heaters.

  • It takes time to put in and take out hot water.
  • Inconsistent water temperature when multiple outlets are active at the same time.
  • You cannot get hot water during a power outage.

Investing in a water heater is a difficult decision. Therefore, it is important to understand all the facts before making a decision. In this article, I provide a comprehensive list of the pros and cons of water heaters so that you can make informed decisions based on your unique situation.

There are many options on the market when investing in a new water heater for your home. Should you pay with a traditional water heater to keep the water warm? Or is a water heater a better option? We have compiled a list of the strengths and weaknesses of ready-to-use water heaters to help you decide which one is best for you and your family.

Let’s get in right away. Click the link below to jump to the section.


Advantages of instant water heaters: 

Pros: Long-term energy

Pros. Save money and energy

Pros. Unlimited hot water supply

Pros. Less space

Pros. Long life

Pros. Less risk of leaks and floods

Pros. No risk of tank explosion

Pros.  Low risk of burns and exposure to toxic metals

Pros: Life expectancy over 20 years

Pros. Long-term energy 


The main advantage of water heaters is that they are energy efficient and save money in the long run.

Tank water heaters use energy all day to maintain a water supply temperature of 40-50 gallons, making hot water available when needed. As the name implies, instant water heaters heat water as needed and do not maintain a water supply.

When heated only when water is needed, there is no standby heat loss due to the instantaneous water heater that occurs when the heat escapes from the water tank and needs to be continuously heated. The faucets, showers, and appliances are open, cold water flows through the water heater, where it is heated by a gas burner or electric coil.

When the water is heated (this happens within seconds), the hot water flows through the pipes and comes out of the faucet, showerhead, or other outlets in the house

How much energy do you save?

Energy savings depend on the amount of water used and the efficiency of previous tank systems.

According to the US Department of Energy, tankless water heaters can be 8% to 50% more energy-efficient than tankless water heaters, but the actual efficiency depends on the amount of hot water used.

If you are using less than 41 liters of hot water per day, tankless heating is 24-34% more efficient than tank heating.

If you are using a large amount of about 86 gallons of hot water per day, the efficiency is only 8-14% higher because the tankless water heater runs more often.

You can save even more by installing an instant water heater at each outlet (shower/sink) instead of the central system of the entire house. Between 27% and 50%.

Switching from a water heater to a tankless water heater can save an average of $ 100 a year for a family of four, or more than $ 1500 for the entire system life, according to Energy Star.

Pros. Save money and energy

Instant water heaters save energy and money. Traditional water heaters are insulated, but insulation is not intended to prevent heat loss. Traditional water heaters continuously heat the water in the tank to supply hot water when needed. This constant heating can be added to the total monthly cost of electricity. One of the benefits of buying a water heater is that it consumes less energy, is faster, and more affordable.

Pros. Unlimited hot water supply

This is the scenario. You go home from the day on the beach with your family and everyone in the house needs to take a shower. If you take a shower 5 times in a row, hot water will come out and you will take a cold shower.

If you have a water heater, you will never find yourself in this scenario. Please let me explain.

Each instant water heater has a maximum flow rate. In other words, they can only heat a certain amount of water at a given time.

Most instant water heaters can’t keep up if five showers are running at the same time.

As long as the water consumption at a given point is below the maximum permissible flow rate, the instant water heater will provide an infinite amount of hot water.

Convenience water heaters heat water from the outside as needed, so you can take a shower for 10 hours (or more) and the water is as hot as a 10-minute shower.

A related topic, Tankless Water Heater Installation Cost 

Pros. Take up less space

Instant water heaters are a great advantage when space in your home is limited. They are usually wall-mounted and take up much less space than water heaters.

To see how big the tank and tank water heater are, the 40-50 gallon medium tank radiator is 54-60 inches, 20 inches in diameter, and cylindrical.

The average unit without a tank is approximately 27 inches high, 18 inches wide, 10 inches deep, and rectangular.

Tank heaters typically occupy basement space, but tankless units such as circuit breakers are wall-mounted and fit in most cabinets.

A 40-60 gallon water heater occupies a lot of space in the laundry room or closet. One of the benefits of installing a water heater is its low form factor. These heaters occupy less than half the space of traditional water heaters, saving valuable space in your home.

Pros. Less risk of leaks and floods

Over time, one of the greatest risks of tank heaters is the accumulation of minerals from hard water in the tank, causing corrosion and eventually leaking.

Since the instant water heater does not have a tank, there is no risk of water leakage or inundation.

This does not mean that the water heater is immune without problems. Problems that can lead to leaks can occur, but large leaks are unlikely to flood the entire basement and cause serious damage.

Pros. No risk of tank explosion

In today’s installation cords, all water heaters require a temperature and pressure relief valve that opens to release pressure and eliminate the possibility of the tank exploding.

Over time, mineral and water deposits can clog the valve and prevent it from functioning properly.

In this case, dangerous pressure increases and can be at risk. If you have a tank water heater, experts recommend testing the valve at least once a year.

Although rare, a water heater explosion is a serious risk. Fortunately, there is no danger of explosion because there is no tankless heater. One less thing to worry about.

Pros. Low risk of burns and exposure to toxic metals

Many experts claim that instant water heaters are safer than instant water heaters.

In addition to having no tanks that can explode, it provides more accurate temperature control, reducing the chance of getting burned with hot water.

As I said earlier, tank heaters fail over time due to hard water, leading to rust and corrosion on the tank lining.

These minerals and particles eventually enter the water pipes, exposing the family to harmful toxins.

Convenience water heaters cannot maintain water supply in corroded tanks, so the water distributed throughout the home is cleaner and safer.

Pros. Life expectancy over 20 years

The average service life of an instant water heater is 8 to 12 years, while the average service life of an instant water heater is more than 20 years.

If you are already in your “eternal home” or plan to stay where you are for a while, investing in a water heater will save you a long exchange.


Cons: High Upfront Cost of the Unit and Installation

The biggest drawback of instant water heaters is the high acquisition cost of devices and installation.

According to HomeAdvisor, the average cost of a 40-50 gallon water heater, including installation, is $ 889. The average cost of a tankless water heater, including installation, is $ 3,000.

Instant water heaters are more expensive, mainly due to their high installation costs. It is often necessary to install special wiring or install new vent pipes to handle the increased load.

Tank heaters have been used for a long time and are used frequently, so more specialists can be installed and labor costs can be kept low.

In addition, hard water (water with a high mineral content) can make tankless water heaters more difficult to operate and eventually fail.

Because of this risk, some manufacturers also require the installation of water softening systems. Failure to do so will void the warranty. Installing this add-on will increase the total cost.

Con: Take Longer to Deliver Hot Water

Another downside of a tankless water heater is that they take longer to generate and supply hot water than instant water heaters.

Keep in mind that instant water heaters cannot supply hot water when needed.

When the hot water tap is turned on, the idle water in the pipe will be cold or at maximum room temperature.

Hot water comes out as soon as the cold water drains. However, it may take a few seconds to a minute, depending on the distance between the heater and the tap.

The tank heater does not produce hot water immediately, but it arrives early at the exit because it is ready and does not need to be turned on.

Cons: Coldwater sandwich

In your search for an instant water heater, you’ve probably come across the term “cold water sandwich”.

Coldwater sandwiches occur when hot water is used intermittently, first with a sensation of hot water, and then when the cold water heats up rapidly.

If you turn the hot water off and on quickly, like when you wash the dishes by hand, the pipe will contain the previous hot water.

A short delay from the start of the stream to the heater causes a short burst before the cold water warms up. The feel of a cold water sandwich isn’t a big deal, but it can be daunting if you’re not used to it.

Cons: Inconsistent water temperature when using multiple faucets/showers/devices

At the beginning of this article, we talked about a scenario where your family came home from a day on the beach, and everyone needed to take a shower.

The advantage of an instant water heater in this scenario is that the whole family can take a shower one at a time without worrying about running out of hot water. The downside is that the tankless water heater cannot keep up with multiple showers running at the same time.

This is not just a shower issue. Depending on the size of the water heater, running the shower and dishwasher at the same time can cause problems.

Flow rate is the most important indicator to keep in mind when buying an instant water heater.

The flow rate is the amount of water that the tankless unit can heat at any time. Measured in gallons/minute or GPM. The higher the GPG, the more water can be heated at the same time.

Cons: Difficult to get a lukewarm temperature

One of the lesser-known downsides of the tankless water heater of water heaters is the difficulty in raising the temperature of lukewarm water.

Instant water heaters require a minimal stream of water before they start, so there is a gap between completely cold hot and cold water that can be created with a mixture of hot and cold water. 

It’s not the end of the world, as there are few scenarios where you can’t get the temperature you need, but it’s worth mentioning if you’re the type of person who really loves cool showers.

Cons: No access to hot water during a power outage

When a storm comes and the electricity in the house goes out, the hot water also drops. 

Instantaneous water heaters can be operated with gas or electricity, but gas-operated instant water heaters also require an electrical control panel to operate the system. No matter what type of instant water heater you have, the hot water will run out in the event of a power outage. 

This is one area where bathtub heaters have greater advantages over tankless ones. Regardless of the power source, the water stored in the tank remains hot for several days.

The Downside of a Tankless Water Heater Is Drainage

With a spare of 40 to 60 gallons at any time, traditional water heaters can move at higher levels, allowing more people to take a shower, wash dishes, and run the washing machine at the same time. The disadvantage of instant water heaters is that they reduce hot water production. If you use the dishwasher and shower at the same time, you will easily run out of hot water. 

Energy requirements

Whether you choose an electric water heater or a gas water heater, you need to be careful about generating the enormous amount of energy needed to start the water heater. Traditional water heaters are reserved, so less energy is used to heat the water over time. Water heaters use a lot of energy to produce hot water in your home. In some cases, you may need to choose electricity instead of gas for your water heater, depending on the amount of instantaneous energy available from the gas or electrical connection.

High initial cost

Tankless water heaters have a long life cycle, but the downside of a tankless water heater this type of water heater is the high initial cost. Depending on the model you are comparing, tankless water heaters can be $ 200 to $ 300 more expensive than traditional tankless water heaters. These additional costs may not affect your purchase decision, as you will save even more on your monthly electricity bill.

Whether you’re using a traditional water heater or an instant water heater, ServiceMark’s certified installer team can help. Homes in Pennsylvania and Delaware offer reliable plumbing services, including B. Repair of water heaters, installation of water pipes, cleaning of drainage pipes.

Call a team of certified technicians ((410) 517-7962) for assistance. With over 100 hours of technical training each year, our plumbing professionals help you stay up-to-date on the latest developments and technologies in your housing system and choose the best option for your space.

What are the advantages and disadvantages of a tankless water heater?


  • Water heaters save money over time, thanks to their much higher energy efficiency.
  • They have a much longer service life than water heaters, some of which last almost twice as long.
  • They take up much less storage space than water heaters with storage tanks.
  • You have unlimited hot water whenever you need it. Hot water is usually available in seconds, not the amount needed to heat the tank.
  • There is enough hot water to run multiple showers and devices at the same time.


  • Instant water heaters generally have a higher initial cost than traditional water heaters.
  • The downside of a tankless water heater installation can be costly, depending on the extent of retrofitting required (if any).
  • If the maximum utilization is calculated incorrectly, it can result in an “Issue Challenge”. Fortunately, to avoid this issue, there are tools that help the installer choose the right drive.

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