What Is The Difference Between A Hot Water Boiler And A Water Heater?


 A hot water boiler may not be the most common heating source in the US, but it is widely used in places like the UK due to its reliability and high level of efficiency. Water heaters are a common sight but serve a very different purpose from a boiler and provide hot water on demand for use in your home.

What’s the Difference Between A Hot Water Boiler and A Water Heater

A hot water heater and a hot water boiler may have similar sounding names, but they fill very different purposes inside your home. A hot water heater provides hot potable water on demand, while a boiler can be used to keep your home warm and comfy in the colder months.

Both units are frequently found in homes in the UK, US, and Australia, and it is recommended that each one receive an annual inspection to ensure they are in proper working order and that necessary maintenance is performed promptly.

What Is A Hot Water Heater?

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A water heater is a large tank that can heat up water that is used in the home. The hot water that you use in your bathroom, kitchen, and other fixtures comes from this tank, and the water is periodically heated to keep it warm over an extended period of time.

Hot water heaters also work to store water that has been heated and can warm water to reasonably high temperatures. If your water heater is set too high, it is possible to burn yourself on the hot water that comes out of the tap.

Some water heaters do not have a tank, and these are called tankless water heaters. These units have an internal heating mechanism that heats the requested hot water on demand without the need to store it and reheat it until it is used.

Tankless hot water heaters generally look box-like and are somewhat smaller than boilers. They can range in size but are usually small enough to hang on the wall and look like a sizeable electrical style box. They are frequently hidden in small areas like stairwells, closets, and utility rooms where space is limited.

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How Does It Work?

How water heaters can run on a variety of fuel sources including gas, electricity, and even solar. Solar powered hot water heaters may use passive heating or may be directly powered by electricity that is collected using solar panels.

A water heater with a tank works by taking cold water and warming it using indirect heat provided by rods inside the tank. The inside of the tank may also include a gas burner if the hot water heater is gas powered, and this serves the same purpose of warming the water.

Periodically the rods or burner will turn on to keep the temperature of the water as warm. On the side of a hot water tank, there is traditionally a dial or interface for setting the water temperature required.


The drawback to a water heater with a tank are:

  • Eventually, the tank will need to refill, and at that point, it will need more time to heat the hot water.
  • When the hot water runs out, cooler water will run through the pipes to the tap.

Water heaters with a tank are also seen as being less energy efficient than their tank less counterparts as they must run intermittently to keep the water temperature up for when the water is needed. A tankless water heater produces hot water on demand and never runs out of hot water.

Water heaters that have a tank are also quite large and take up considerably more space than tankless water heaters. It is also advisable to keep other objects a safe distance away from a tank style water heater to prevent fire hazards and damage should it leak.

Tankless water heaters are much more contained and roughly the size of a large backpack, so they can fit practically anywhere. Since they do not hold quantities of water, there is also little risk of them leaking or becoming a fire hazard.

What Is A Hot Water Boiler? What Does It Do?

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A hot water boiler is very different than a hot water heater in many ways, but most noticeably different in how they look. How water boilers are a sizeable box-like object that contains a series of pipes that water runs through before becoming steam.

As the water runs through the pipes, it is heated by a gas burner in the bottom which it hot enough to turn the water into steam. This steam can be pumped through the home to provide heat and can also be used to heat more massive complexes and spaces such as swimming pools.

Heating the water and running it as a heating source is more efficient as water is better at holding heat than air. The water for a hot water boiler does not need to be potable, but it can still be used as part of a home’s radiant heating system and run through the pipes located in a home’s walls.

A boiler will also have an exhaust, much like a hot water heater, that serves as an escape route for fumes created by the gas burner in the boiler. Boilers are very powerful and frequently take a bit of energy to run, but they can heat large pools, hot tubs, and even large complexes quite efficiently.

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Controls and Fuel

A boiler will also have much more complex controls than a hot water heater, and fine-tuning of these controls may be required. Since the unit can produce more heat and receive more complex information about where that heat should go, there is more than just a simple dial as is often the case on a hot water heater.

Boilers can run on natural gas, propane, electricity, and alternative fuels such as wood. Although many boilers can be powered by solar panels that create electricity, larger ones will need to be connected to the power grid to have enough power to run.

For smaller spaces, wood pellets are frequently used, and smaller units are substituted that are more appropriately sized. The boilers used to heat large complexes can often require their own utility room and large pipes that create a web that spans across the floor and walls of every space that needs to be heated.

A thermostat is an essential part of the heating system when using a boiler as its this device that tells the boiler when to turn on. Thermostats are often programmable and can frequently be controlled remotely.

Advantages of a Boiler

A boiler is an excellent example of a closed loop system that uses the same water to heat a space over and over again. When the water is heated, it turns into steam and is pushed through pipes to create heat in an area. Once the steam has transferred its heat, it becomes water again and flows back to the boiler to repeat the warming process.

Warm water flowing back to the boiler takes less power to heat up again and become steam, and this can result in energy savings. Properly insulating your home and the pipes that run to and from your boiler can also help increase the efficiency of the heat in your home and ensure that space is warmed evenly.

Do I Need Both in My Home?

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Since a hot water heater and boiler serve different purposes, you’ll need to have both in your home if you choose to use a boiler for heat. Hot water heaters are unable to raise the ambient air temperature in your home, and boilers are not suitable for heating hot water used for showering, cleaning, and cooking.

Modern boilers and hot water heaters both have the potential to be much more energy efficient than older models of the past. Boilers, in particular, can heat the air in a forced air system, and also provide heated floors in your home if the proper hardware is installed.

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Are Both Units Covered by My Home Warranty?

This question can be tricky given that it will largely depend on your particular home warranty and the area in which you live. Many home warranties will cover hot water heaters, but they may not cover boilers.

When your hot water heater breaks down, you can call your home warranty company, and they will have you contact a contractor to diagnose the issue with the unit. For those that don’t have a home warranty in place, they would need to find their own contractor to do the inspection and repair and pay out of pocket.

Once the issue is diagnosed, depending on the home warranty contract, it may be covered and the repair performed by the contractor would be free. Boilers are less widely used in the United States in particular and are generally considered to be an appliance instead of a system.

As a result, in the US many home warranties do not cover boilers, and it can be more difficult to find experts or repair people who can diagnose issues with a boiler. Fortunately, a boiler is generally a reliable unit, and with regular use and maintenance, it can last a long time.

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Boiler Maintenance Tips

To ensure the continued health of your boiler, consider getting a regular annual inspection to confirm it is in proper working order, and to complete any preventative maintenance. An online search should suggest experts in your area that have experience and positive references.

Make sure to regularly check your water boiler for leaks and other cracks that may be forming in the pipes that lead to the unit. Check vent pipes carefully for holes, and make sure that all seals appear to be intact and not cracked.

Gas powered boilers have the potential to create carbon monoxide, so it’s a good idea to get a carbon monoxide detector in your home to alert you promptly of any leaks.

You’ll also want to clean away any debris or rust that forms around or on your boiler that might prevent it from running correctly. Cleaning the sides and the surrounding area will also prevent dirt and corrosion from getting into the boiler that might make the unit less efficient.

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Hot Water Heater Maintenance Tips

It’s a good idea to get an annual inspection for your hot water heater, but this is something that you can also perform yourself. Each year you’ll want to drain your hot water tank to remove dirt and sediment that forms at the bottom of the tank.

This dirt and sediment can cause corrosion in the tank and may ultimately make it less efficient and more likely to leak. Double check the temperature dial on the side and make sure that it is set correctly. 120 degrees is generally the recommended temp, but for every 10 degrees lower you may potentially see a 5% reduction in energy costs.

If you are planning to go on vacation, or won’t be in your home for a few days, you can turn your water heater to its lowest setting to save energy and prevent the water heater from running and keeping water hot while you are away.

Many water heaters have a “vacation” setting on their temperature dial but setting it to the lowest temperature works just as well. If your hot water heater doesn’t already have a layer of insulation around it, you can add that to help the tank maintain its temperature and potentially gather even more energy savings.

On the side of the water heater, near the top, you may also notice a valve called the Temperature-Pressure-Release or TPR valve. This valve is a safety measure that relieves pressure should the inside of the tank become too pressurized.

To make sure this valve is working correctly you’ll want to put a bucket at the base of the pipe its connected to, and lift the handle of the valve to let some of the water out. Once you have let a small amount of water out, you can let go and look to see if the water continues to flow.

If you see water continuing to come out for more than a second or two, its time to partially drain your water tank and turn it off to replace the TPR valve. The valve easily screws off with a pipe wrench and replacements can be purchased at a local hardware store.

Last update on 2021-09-18 at 01:41 / Affiliate links / Images from Amazon Product Advertising API


  1. Thank you for explaining that dirt and sediment in a water heater can cause corrosion in the tank. My sister is thinking about getting a new water heater since hers has only been giving her cold water. I wonder if she should first see if any repairs can be done.

    1. You can certainly try. Draining the heater is the first thing I would do. Sometimes if the sediment isn’t baked to the bottom of the tank if will run out of the drain. I will say that if she isn’t getting any hot water from the unit it is probably a bigger issue.m

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