Tankless Water Heater vs. Boiler: What’s the Difference?

Comparison, Tankless Water Heater

tankless hot water heater vs boiler
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Tankless Water Heater vs. Boiler: What’s the WHOA?

Today, I’m gonna end this age-old debate regarding the major differences between a tankless heater and a boiler.

In this post, we would be covering the below topics in order to help you with the necessary piece of information for which you’ve landed on this post.

  • What is a boiler?
  • Working principle of a boiler
  • Types of boiler
  • Maintenance of a boiler
  • What is a tankless water heater
  • Working principle of a water heater
  • Types of water heater
  • Maintenance of a water heater

So, without any further ado, let’s begin…

What is a boiler?

You can think boiler as a closed vessel that is used for heating water or any other liquid in order to generate vapor and steam.

It wouldn’t be wrong if I’ll say that boiler is a misleading term in itself as it doesn’t boil water rather turn the liquid form of water into gas.

One of the many benefits of a boiler is that it can heat water very rapidly and hot water heaters are available in both tankless and tanked versions.

Unlike a tank-style heater, in a boiler, the tank store cold water while the cylinder holds hot water.

How does a boiler work?

Well, a boiler is nothing but a water-containing vessel that is meant to transfer heat from a fuel source such as oil, gas, and coal into steam which is piped to a point so that it can be used for multiple things including running production equipment, to sterilize, provide heat, etc.

Moreover, the energy given up the steam is sufficient to convert it back into the form of water.

When 100% of the steam produced is returned to be reused, the system is called a closed system.

Examples of closed systems are closed steam heating, hot water heating, and “one-pipe” systems.

Since some processes can contaminate the steam, so it is not always desirable to feed the condensate back into the boiler.

A system that doesn’t return the condensate is called an open system.

Boiler Types

Let’s have a quick look at some of the important types of boilers.

Combination: These types of boilers are mainly used for supplying hot water as well as heat for your home, restaurant, etc. Since it doesn’t comprise either a cold water tank or a hot water cylinder so can be easily installed in small spaces. Don’t worry, it is capable of supplying unlimited hot water.

System: They are the ones that don’t require a cold water tank but do possesses a hot water cylinder. In fact, water directly comes from the main then is heated and stored in the cylinder. The hot water capacity is limited by its size of which there are options. However, if you’ll run out of hot water then you’ll have to wait until the cold water gets heated to the desired temperature and stored again.

Conventional: As the name suggests, a conventional boiler comes with a cold water tank and a hot water cylinder so it might not be suitable for small spaces. Needless to say, it occupies a decent amount of space. To be honest, you don’t need a conventional boiler for small apartments. In case, you own a big apartment wherein you run a number of faucets, and showers at once.

Condensing: Frankly speaking, I don’t find condensing type of boiler even a boiler rather more of an attribute that a boiler can have. At times, they prove to be more energy efficient because of their ability to retain heat.

Fire Tube Boiler: They are the ones in which fire or hot gases are present inside the tubes and water surrounds these fire tubes. Since the fire is present inside the tube so they are named fire tube boiler. The heat from the hot gases is conducted through the walls of the tube to the water. Some of the well-known examples of the fire tube boiler are Velcon boiler, Cornish boiler, etc.

Water Tube Boiler: In a water tube boiler, water is present inside the tube, and fire or hot gases surrounds the water tube. Benson boiler, Stirling boiler, Babcock boiler are some of the well-known examples.

Single Tube Boiler: These types of boilers contain either one fire tube or a water tube, and hence, called a single tube boiler. Simple vertical boiler and Cornish boiler are two very popular examples of a single tube boiler.

Multi-tubular Boiler: Well, multi-tubular boilers are the ones that come with two or more water or fire tubes. Lancashire boiler, Locomotive boiler, Cochran boiler are some of the popular examples of the multi-tubular boiler.

Internally Fired Boiler: As the name suggests, internally fired boilers are the ones in which the furnace is located inside the boiler shell. Many of you wouldn’t be aware of the fact that among all the fire tube boilers, most of them are internally fired boilers.

Externally Fired Boiler: In an externally fired boiler, the furnace is located outside the boiler shell. In this type of system, the furnace is arranged underneath in a brickwork setting. Water-tube boilers are always externally fired boilers.

Vertical Boiler: The vertical boilers are the ones in which the axis of the shell is vertical. Simple vertical boiler and Cochran boiler are some of the examples.

Horizontal Boiler: The horizontal boilers are the ones in which the axis of the shell is horizontal. Locomotive boilers mostly fall in this category.

Natural Circulation Boiler: The natural circulation boiler is the one in which circulation of water takes place naturally by the convection currents that set up during the heating of water. In most of the boilers, you’ll find natural circulation of water such as Lancashire boiler, Cochran boiler, etc.

Forced Circulation Boiler: In these types of boilers, the water circulation takes place with the help of a centrifugal pump driven by some external power. Just for your information, forced circulation is used in high-pressure boilers such as Benson boiler, La-Mont Boiler, etc

Stationary Boiler: As the name suggests, stationary boilers are the ones that are literally stationary and can’t be moved from one place to another. Once they are installed, they cannot be transported from one place to another. Mostly, you’ll find such boilers in power plants as well as industrial process works.

Mobile Boiler: From the name itself, you can guess that mobile boilers are the ones that can be easily transported from one place to another without any hassle. Locomotive and marine boilers are the best examples for this category of boilers.

Maintaining A Boiler

It goes without saying that proper maintenance is required for your boiler to last longer.

In case, you’re like me and prefer to maintain the boiler yourself then you need to focus on the below-mentioned areas.

  • Keep vents and flues clean in case, you’ve them
  • Check water levels monthly as lack of water can cause serious harm to the system
  • You need to check for leaks on a frequent basis in order to prevent any last hour misadventure
  • Another important step involved in the maintenance is de-scaling which involves cleaning of hot water that leads to lime buildup
  • And, most importantly, don’t forget to lubricate moving parts every six months
  • Finally, flush out all water every six months and cleans thoroughly

To sum up, I’ve tried to the best of my capabilities to share all the necessary pieces of information related to a boiler that I’ve gained over a period of time.

Moving further, we would be discussing various aspects of tankless hot water in order to help you make an informed decision.


Tankless Water Heaters

Well, tankless water heaters are popularly known as demand-type or instantaneous water heaters and provide hot water only when you need it.

As the name suggests, tankless hot water heaters don’t come with a tank and so standby heat loss is almost negligible.

As a result, you can expect a tangible reduction on your water heating bills.

Most of the tankless hot water heaters last for almost 20 years and can be installed in small spaces as well because of their small, compact, and sleek design.

Most of the tankless hot water heaters can be easily installed and are also equipped with advanced and innovative technology in order to help the end-users achieve optimum results.

How A Tankless Hot Water Works?

The working mechanism of a tankless hot water heater is quite different from a tank-styled heater.

When a hot water tap is turned on, cold water travels through a pipe into the unit.

Either a gas burner or an electric element heats the water.

Just for your information, there are two popular types of tankless water heaters, that is, gas tankless water heater, and electric tankless water heater.

A gas tankless water heater can be further segregated into a propane tankless water heater and natural gas tankless water heater.

The tankless water heater has become very popular in recent times because of its ability to provide you instant hot water by cutting the wait time tangibly.

Well, enough of bragging about tankless heaters, right?

On the downside, a tankless water heater’s output limits the flow rate.

Most of the tankless water heaters that I’ve known over the decade provide hot water at a rate of 2-5 gallons per minute.

Moreover, gas-fired tankless water heaters produce higher flow rates than electric ones.

If I’m not wrong, sometimes even the largest and the most powerful gas-fired model wouldn’t be able to supply sufficient hot water for simultaneous, multiple uses in large households.

Let’s understand it with a simple example.

Suppose if you’re taking a shower and running the dishwasher at the same time, then it can stretch a tankless water heater to its limit.

However, the good news is, you can overcome this problem.

All you need to do is to install two or more tankless water heaters, and then connect them in parallel for simultaneous demands of hot water.

What else you can do is install separate tankless water heaters for appliances such as a cloth washer or dishwater that use a lot of hot water in your home.

Tankless hot water heaters can be used for the below applications as well.

  • Remote bathrooms or hot tubs
  • Booster for appliances such as dishwashers or clothes washers
  • Booster for a solar water heating system

Pros and Cons of a Tankless Water Heater

Let’s have a quick look at the pros and cons of a tankless water heater.


  • Instant hot water
  • Longer lifespan
  • Lower month-on-month cost
  • Space-saving
  • Special financing and tax breaks
  • Eliminates standby loss
  • Never run out of hot water
  • Both electric and gas models are available
  • A tankless hot water heater offers longer warranties
  • Definitely, a perfect choice for a small or medium-sized home with minimal hot water requirements


  • Inconsistent temperature
  • Higher initial cost
  • Limited hot water supply
  • Additional equipment is often necessary
  • Rerouting gas lines
  • Might take years to make up for the higher price tag

Tankless Hot Water Heater: Installation and Maintenance

It goes without saying, installation and maintenance play a crucial role when it comes to comparing two tankless models.

Proper installation and maintenance of your hot water heater can definitely enhance its lifespan and of course, for a good reason.

In fact, it can optimize its energy efficiency.

Proper installation depends on many factors.

These factors include fuel type, climate, local building code requirements, and safety issues, especially concerning the combustion of gas-fired water heaters.

Furthermore, it’s best to have a qualified plumbing and heating contractor install your hot water.

Do the following when selecting a contractor.

  • Request cost estimates in writing
  • Ask for reference
  • Check the company with your local better business bureau
  • See if a company will obtain a local permit, and always good to understand local building codes

I highly recommend you to consult the manufacturer in case, you’re determined to install the water heater yourself.

Well, manufacturers usually have the necessary installation and instruction models.

Also, contact your city or town for information about obtaining a permit, if necessary, and about local water heater installation codes.

Furthermore, periodic water heater maintenance can significantly extend your water heater’s life and minimize loss of efficiency.

And, of course, don’t forget, to read your owner’s manual for specific maintenance recommendations.

Improve Energy Efficiency

Well, once you’ve properly installed a hot water heater, the next thing that you need to do is to improve the energy efficiency so that you can reap the benefits in the long-run.

One of the easiest ways to do so is to expedite the maintenance task on a regular basis.

Furthermore, you can also try some additional energy-saving strategies in order to lower your water heating bills.

Just for your information, some energy-saving devices and systems are more cost-effective to install with a water heater.

Wrapping Up Tankless Water Heater vs. Boiler

First and foremost, I would like to thank you for being with us till the end.

Secondly, I would like to bring to your notice that I along with my core team have put loads and loads of effort into coming up with this idiosyncratic superlative comprehensive guide.

And, in case, you want to appreciate us, then feel free to share this piece of information with the ones who are in need of it.

After all, sharing is caring, isn’t it?

Please do let us know in case, we’ve missed out on some points.

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