Compare Boilers vs. Water Heaters and Buy the Best Type

Many of us are unclear about the differences between boilers and water heaters, so if you are, you are not alone.

Here we will highlight the differences (and similarities) between boilers and their cousins, water heaters, and look at which may be best for your requirements, especially if you plan to change how you heat your home and your water.

Boilers vs. water heaters: Things to consider

What are the differences between boilers and water heaters and how they work?

What are boilers?

Gas boilerGas boiler

Boilers and water heaters are often confused as being the same thing, but they are not. Yes, they do both heat water, but beyond that, there are big differences.

Boilers are designed to heat non-potable water by using natural gas, propane gas, oil, and electricity as energy sources. The heated water is then delivered to the baseboard or traditional radiators, hydronic floor, or ceiling-mounted systems for space heating. Some boiler types can also produce and use steam.

Boilers can also heat potable water for your household needs, but indirectly. This is normally done by a heat exchanger running between the boiler and a large water storage tank, heating fresh water for your domestic use. The boiler will fire up when the water temperature drops, so it reheats it to a preset level.

What are water heaters?

Gas water heaterGas water heater

On the other hand, water heaters are designed to do what it says on the can – heat water. They are not used to power your home heating system; they only heat water and store it in a large tank ready for use.

Depending on your needs, they can be electric, gas, fuel oil, or solar-powered and commonly store between 20 and around 100 gallons of hot water.

So, if you only have a water heater, you will need a separate system to heat your home, like a furnace, boiler, or heat pump, for example, because most water heaters will not do that for you.

Boilers vs. water heaters - Comparing differences


  • Water is not safe for human consumption
  • Uses hot water or steam to heat the space or potable water
  • Complex system
  • It requires a lot of space
  • Expensive

Water heater

  • Water is safe for consumption
  • It is used only for water heating
  • Simple controls
  • Smaller footprint
  • Affordable

Types of boilers

Boilers come in many different categories and varieties:

Hot water boilers often utilize a gas or oil burner to heat the non-potable water and pumps to circulate hot water to the radiators, baseboards, or hydronic floor system where it radiates the heat.

Steam boilers are designed to heat water and turn it into steam, and then use pressure and gravity to deliver hot steam to radiators.

Standard (conventional) boilers require a cold-water storage tank as well as a tank for hot water, so their space requirements are significant.

System boilers utilize two parts: a boiler and a hot water cylinder. There is no cold water storage tank as in conventional boilers, so they are simpler to install while saving you space. Boilers heat up your water which is then stored in the cylinder.

Combination or combi boilers, as the name suggests, provide heating for your home but instead of storing hot water in a large tank, it also heats water as required on demand, so the boiler will kick in when hot water is called for anywhere in your home.

There are also other options available to you:

  • Gas boilers
  • Oil boilers
  • Electric boilers
  • Biomass boilers
  • Condensing boilers

Types of water heaters

Water heaters are typically divided into several categories:

  • Tank-type water heaters
  • Tankless
  • Indirect

Tank-type water heaters are designed to store and heat potable water only.

Tankless water heaters heat water only on demand and deliver it in an endless supply. They are efficient and powerful but small enough to save on space.

Indirect water heaters are designed to use a space heating system, such as a furnace or boiler, to heat the water inside the storage tank.

The type of a boiler or water heater you will choose depends on many factors, including:

  • Your budget
  • Available space
  • Size of your home, number of occupants, and bathrooms
  • Hot water requirements

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Pros & cons

The main benefit of standard water heaters is they are cheap to buy, reliable, and, if regularly maintained, will deliver excellent service for between 10 and 15 years.

They do take up a reasonable amount of space, but if there has been one fitted to your home previously, the space will have been created when the house was built. Often, they are located in a garage or utility room. Modern water heaters are slimmer and more efficient today than ever before, but they are large, especially if you need the 80-gallon size.

If you have an existing boiler supplying heating and hot water to your home, then you probably won’t need a separate water heater unless your boiler is due for replacement, or your needs are greater than the boiler can deliver, then it may be a good time to consider your options.

You could investigate the benefits of tankless water heaters and reduce your energy costs from heating and reheating a large tank of hot water over and over. These units are much more compact, can be installed outside, and have substantially lower energy costs. However, it is essential to ensure you buy the correct size unit for your home, or you could run out of hot water if the heater is too small for your demands.

Seek professional help in selecting the right one.

The downside is tankless water heaters are more expensive to buy and install and require a certain minimum water pressure to work correctly. They also need filtration, especially if your water source is from a well and in hard water areas; water softening may also be required.

Modern combination (combi) boilers do not require a hot water storage tank, and they use a heat exchanger built into the boiler to deliver hot water on demand in the same way a tankless water heater does. They are compact in size and efficient at carrying out both home heating and your water heating requirements, so the savings in space and energy make them well worth considering.

Combi boilers and standard boilers are most efficient in cooler climates where your home heating operates longer each year. The reason is, to heat your water during the summer, your boiler has to fire up as water is called for. So, like any boiler-heated water, it’s less efficient in warmer climates.

Benefits & considerations

All of us are looking to reduce energy costs, specifically for heating and air conditioning, because the two together account for over 50% of the power costs in the average home.

Of course, usage is seasonal and will depend on a number of factors like location, home size, levels of insulation, and type of energy used.  A further 27% is consumed by only three things – water heating, lighting, and refrigeration, all used throughout the year, everywhere.

In Canada, energy usage is split in a similar way but, of course, varies across the country depending on which province you live in. So, it’s clear that any way you can save your energy costs, especially in home and water heating, will deliver the most savings on your budget. 

Assessing your energy type and supplier to get the best deal is essential. You may not wish to change the type of energy you use; however, it pays to keep an eye on offers available to change suppliers, as they often have deals to get new clients.

Check the details carefully and avoid lock-ins committing you to several years, where possible. You could find substantial savings by swapping, and it’s usually easy and painless to do.

If you are in the market for a new boiler or water heater, carefully check what’s available. What do your neighbors or family use?

Seek professional help when sizing the system you are considering because mistakes at this stage can be costly to remedy later on if you get it wrong.

If you have a large home, then a boiler with a large storage tank for hot water may be your best bet. The footprint is large so that you will need space, but it is an efficient method of heating your home and hot water, and these systems are generally energy-efficient.

If space is limited, then you could consider a combination (combi) boiler which will heat your home and provide you an endless supply of hot water on demand. But remember, size matters, so that’s where your friendly local professional will help you size things up accurately.

If you decide to go with a standard water heater tank, then seek out the best deals on the latest models. Check sizing again, and specifications then select the correct one for your home.

Choose a qualified professional for installation and who will also cover warranty issues. Some suppliers will provide a full package, including site inspection, sizing guidance, delivery, installation, and removal of your old unit for safe recycling if you wish.

Tankless water heaters are popular, and the savings in energy are substantial, added to having no standby energy losses make these water heaters a great investment. Again, sizing is critical, or you will have heartache later. You need to consider your hot water usage carefully; how many people live in your home?

How many bathrooms do you have, and the number of anticipated daily showers your family will take? Additionally, the number of items that need hot water in your home, like clothes washers, dishwashers, and so on, all need to be accounted for to ensure you get a unit that will cope with your load.

It is sometimes advisable to fit separate on-demand heaters dedicated to additional bathrooms or clothes washers if your requirements warrant it, but a professional technician will guide you through the sizing maze.

Due diligence done, you can rest assured you have selected the best fit for your specific requirements, remember there is no one-size-fits-all when it comes to home and water heating.


So now, hopefully, you should be clear on the differences between boilers and water heaters and the benefits of each type of system in your home.

The final choices will depend on a number of personal things, so professional input is a worthwhile route to go initially.

Experienced technical advice is valuable at the selection and sizing stage of your project, and it’s usually free of charge, so don’t be afraid to ask for advice.

Once you have the correct information, you can go ahead knowing you are making the right choice for your home and family, and that feels good.

Or, talk to your local plumber if you need professional help.

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