How many people can actually picture what a balance boiler is when they hear the term?
Since they are rarely seen these days, many people may not have a clear image of one.
However, some older apartment buildings still have properties equipped with balance boilers.
In this article, we will explain what a balance boiler is, when to consider replacing one, the associated costs, and key points for choosing a contractor.
If you are unsure about replacing a balance boiler, we hope this article will serve as a useful reference.
What Is a Balance Boiler?
A balance boiler is a bathing system in which a water heater installed beside the bathtub heats the water.
It became widespread in housing complexes in the greater Tokyo area during Japan's period of high economic growth and eventually made its way into ordinary homes, though it is rarely seen today.
Let us begin by explaining what a balance boiler actually is.
Types of Balance Boilers
There are mainly three types of balance boilers.
· Sealed Type
The sealed type draws air from outside and expels exhaust to the outside.
It is divided into two categories: the BF type (balanced flue), which uses natural air intake and exhaust, and the FF type (forced flue), which uses forced air intake and exhaust.
The BF type installs the water heater inside the bathroom.
A hole is made in the bathroom wall so that part of the heater extends to the outside, meaning that from the exterior, the bathroom wall appears to have a square opening with the unit protruding through it.
The FF type offers greater convenience compared to conventional balance boilers, as it allows the use of a shower and temperature control via a remote controller.
The water heater is located inside the bathroom and has a chimney flue that extends slightly to the outside.
· Outdoor Installation Type
The outdoor installation type draws and expels air directly from the unit placed outside.
It is sometimes referred to as the RF type.
No exhaust flue is required, allowing for efficient operation.
A distinctive feature of the outdoor installation type is the inclusion of a heat-completion buzzer and a remote controller with a timer.
The outdoor installation type is available in both wall-mounted and freestanding configurations.
· Semi-Sealed Type
The semi-sealed type draws air from indoors and expels exhaust to the outside.
There are two varieties: the FE type, which uses forced exhaust, and the CF type, which uses natural exhaust.
Both use indoor air for combustion, so a ventilation opening is required.
The FE type is characterized by a chimney flue that exits to the outside facing downward.
The CF type carries a higher risk of exhaust backdraft depending on weather conditions, raising concerns such as carbon monoxide poisoning.
For this reason, if you are using a CF type, it is advisable to replace it with a different type.
The CF type also has a chimney flue that extends all the way to the eaves.
How It Works
A balance boiler has both an air intake and an exhaust port on the water heater installed beside the bathtub.
Air is drawn in through the intake port to combust the gas and heat the water, while the air produced during combustion is expelled through the exhaust port to the outside.
The bathtub also has two holes, from which pipes extend to connect to the water heater.
Water from the bathtub is drawn in through the lower hole, heated by the water heater, and returned to the bathtub through the upper hole.
This cycle is repeated to heat the bathwater.
How to Use a Balance Boiler
A balance boiler may seem complicated, but once you get used to operating it, you will not find it particularly troublesome.
Since it uses gas, careful attention to safety is essential, but if you understand the basics, the likelihood of a serious problem occurring is considered low.
To heat water with a balance boiler, first fill the bathtub with water and open the gas main valve.
Then turn the lever vertically relative to the hose position, align the knob to the "pilot light" setting, and ignite.
Since the knob starts in the "off" position, press and hold it while aligning it.
When you hear a "click-click-click" sound and the "pilot light" indicator flashes to confirm ignition, turn the knob to the "hot water/shower" position.
If ignition is not successful, a gas leak may occur.
If there is no indicator lamp to confirm ignition, check for a flame through the ignition window.
Also, it is important never to forget to close the gas main valve after each use.
Making this a habit is necessary to prevent gas leaks.
Why Balance Boilers Are Declining
Balance boilers are on the decline and are rarely seen today.
Why are they disappearing?
The following three reasons are considered to account for the decline of balance boilers.
· They must be installed beside the bathtub, which takes up space
· Their heating capacity is limited, so reheating takes time and shower water pressure tends to be weak
· Their complex operation leads to frequent issues such as ignition failure and dry firing
As hot water supply systems with greater convenience and safety have become more prevalent, there is no longer any particular reason to continue using balance boilers.
In 1983, Tokyo Gas developed a wall-penetrating bath water heater that utilized existing intake and exhaust openings, and this product became a major hit as a replacement option.
The wall-penetrating bath water heater is considered to have contributed to the decline of balance boilers by enabling automatic hot water supply controlled by a remote controller installed inside the bathroom.
Unlike balance boilers, the bathtub can be made larger, allowing for a more relaxing soak and the ability to fill the bath with water at a stable temperature using simple controls — a welcome improvement for users.
As this coincided with the height of Japan's bubble economy, demand for replacements was extremely high.
However, the electrical work required for the replacement was difficult to carry out, which is why many public housing units and similar properties have remained equipped with balance boilers.
Advantages and Disadvantages of Using a Balance Boiler
While balance boilers are declining in number, they do offer certain advantages unique to this type of system.
For this reason, some people continue to use them.
However, every advantage comes with corresponding disadvantages.
Below, we introduce the advantages and disadvantages of using a balance boiler.
Advantages
The greatest advantage of a balance boiler is that some models can be used even during a power outage.
Battery-operated models can heat water without any issue even when there is no electricity.
This is a significant advantage over types that rely on electrical power.
Some balance boilers can also be operated via a remote controller.
With such a model, you are unlikely to find the unit inconvenient to use.
The ability to reheat bathwater is another advantage of balance boilers.
When family members take turns bathing, the water is likely to cool down by the time the last person gets in, but this is not a problem if reheating is available.
It is also a useful function for those who enjoy long soaks such as half-body baths.
Furthermore, the ability to use the shower independently is another notable advantage.
Since only the balance boiler is needed without a separate bath unit, it is also suitable for those who do not regularly use the bathtub.
Rental properties equipped with a balance boiler tend to have lower rents compared to those with other systems.
As such, they may be worth considering for those who do not need a bathtub and are looking for affordable rental housing.
Disadvantages
One disadvantage of a balance boiler is that it makes the bathtub smaller.
This is because the water heater must be installed beside the bathtub.
The water heater is approximately 30 cm wide, so the bathtub must be made smaller to fit within the bathroom.
For those who want a spacious bathtub to relax in, this can be a source of dissatisfaction.
Balance boilers are also designed with a small burner capacity.
As a result, weak shower water pressure is another disadvantage worth noting.
It is said that this issue can be improved by switching to a water-saving showerhead, so it may be worth trying if this is a concern.
Because balance boilers are susceptible to the effects of outside temperatures, some users find that the bathwater cools down too quickly.
Heat retention cannot be expected to be particularly high, which makes this especially noticeable in winter.
Cleaning can also be difficult.
This is because the bathroom contains both the bathtub and the water heater, creating a structure where moisture tends to accumulate in the gaps between them.
Cleaning these gaps is challenging, and mold tends to grow easily.
To maintain a hygienic environment, it is advisable to take measures such as regularly hiring professionals to clean the unit.
Is It Broken? Causes of Balance Boiler Failure
Like any other equipment, balance boilers can break down.
Let us look at some of the common causes of balance boiler failure.
End of Service Life
The lifespan of a bath boiler is around 15 years at most.
The average service life is said to be approximately 13 years.
Barring natural disasters or unexpected incidents, you can generally expect the unit to last that long.
However, deterioration over time is unavoidable.
Prolonged use causes components to degrade, making issues such as ignition failure more likely to occur.
Water Leaks
A balance boiler works by drawing water from the bathtub into the unit, heating it, and returning it to the bathtub.
Since water is constantly moving back and forth, water leaks are relatively common.
Because the water heater is installed right beside the bathtub, there are also many cases where a leak goes unnoticed for some time.
If you notice that the water level drops after reheating, there is a good chance that a water leak has occurred.
Have a professional carry out an inspection.
Rust and Buildup
Since the boiler is constantly exposed to water, it is also prone to rusting.
Scale, grime, and mold also tend to accumulate easily.
Using bath salts or bath additives can increase the likelihood of problems with the boiler, so caution is advised.
If you notice any irregularities or unusual odors during use, stop using the unit immediately.
Consult a professional and consider having it inspected or replaced.
Electrical System Issues
Problems can also occur in the electrical system.
While some balance boilers heat water using gas, the control functions are managed by the electrical system.
If the electrical system — which serves as the control hub — malfunctions, issues such as inconsistent water temperature may arise.
When such a problem occurs, unplugging and replugging the unit may resolve it.
If the problem persists after trying this, there is likely some kind of fault in the electrical system, and you should request an inspection or repair.
Depending on the situation, replacement may be necessary.
When Is It Time to Replace?
If you are using a balance boiler, the time will eventually come to consider replacing it — for instance, when it reaches the end of its service life and begins to malfunction.
Here we explain the signs that indicate it may be time for a replacement.
More Than 10 Years of Use
Balance boilers tend to develop problems more frequently after 10 or more years of use.
Depending on usage, some units may last longer, while others may break down sooner.
As a general guideline, 10 years of use is the benchmark — if your unit has reached that point, it is worth considering a replacement.
In some cases, a full bathroom renovation may be more appropriate than a simple replacement, so take time to consider which option suits your situation before making a decision.
Ignition Failure
If the unit fails to ignite, there is likely a problem with the ignition device or the gas solenoid valve.
If replacing the battery only produces a clicking sound without ignition, the issue may be with the control board or the power plug.
There are various possible causes when a balance boiler fails to ignite, and identifying the root cause is difficult without professional expertise.
If you want to resolve the problem, consult a qualified contractor.
Unusual Odors or Sounds
Unusual sounds or odors are also indicators that replacement should be considered.
If you detect a gas smell or a burning odor, stop using the unit immediately.
Be sure to open windows and doors for ventilation as well.
This is because turning exhaust fans or electrical switches on or off can produce small sparks that may cause ignition.
Additionally, if you hear an explosive sound or an abnormally loud combustion noise when turning the ignition lever, there is a strong possibility that the heat exchanger has failed.
If you notice any of these signs, arrange for an inspection or repair as soon as possible.
Water Won't Heat
If the water stops heating properly or the temperature becomes lower than expected, the cause may be a fault in the water proportional valve, temperature sensor, or electrical system.
Continuing to use the unit in this condition may eventually render it completely unable to heat water, so prompt action is necessary.
In such cases, renovation or replacement will be required.
Replacement or Renovation — Which Is Better?
Unit bathrooms have become increasingly common, but balance boilers still offer certain advantages that other systems cannot match.
That said, when a balance boiler actually breaks down, should you choose replacement or renovation?
Renovating to a Unit Bathroom Is the Best Option
If your balance boiler has aged or begun to malfunction, renovating to a unit bathroom is recommended.
While balance boilers do offer unique advantages such as reheating capability and usability during power outages, it is worth treating a breakdown as an opportunity to renovate.
In general, the lifespan of a balance boiler is considered to be around 10 years.
A unit bathroom not only offers the same reheating function as a balance boiler, but also provides more stable water pressure.
Furthermore, unit bathrooms have a longer service life and offer greater safety during bathing.
Features such as programmable water volume, one-touch temperature adjustment, and automatic top-up functions also enhance bathing comfort.
For these reasons, if you are weighing whether to replace your balance boiler or renovate, renovation is likely the better choice.
Options May Be Limited in Rental Properties
If you are considering replacing a balance boiler with a unit bathroom, you may naturally prefer to upgrade to a unit bathroom.
However, in a rental property, the landlord's wishes take precedence.
If the landlord prefers a like-for-like replacement of the balance boiler, a unit bathroom will not be installed.
Since the balance boiler was originally installed by the landlord, the cost of any repairs or replacements due to malfunction is also borne by the landlord.
If you wish to have a unit bathroom installed at your own expense with the landlord's permission, you must first obtain that permission.
Furthermore, you will be required to restore the property to its original condition upon vacating, which may mean being charged for the cost of reverting from a unit bathroom back to a balance boiler.
Bathtub replacement is a time-consuming construction project that may also inconvenience other residents in the building.
In a rental property, you must follow the instructions and wishes of your landlord.
What Is a Hole-in-One Water Heater?
While balance boilers were once the standard, the trend has shifted toward unit bathroom replacements over time.
Additionally, as balance boilers have become less common, replacement parts have become difficult to obtain.
This has led to an increase in replacements with hole-in-one water heaters.
A hole-in-one water heater is a type of gas water heater, also known as a wall-penetrating water heater.
In housing complexes and similar buildings where balance boilers are still in use, replacement with a hole-in-one water heater is a common option.
A hole-in-one water heater is embedded into the wall opening that was originally made for the balance boiler's intake and exhaust.
This approach frees up the space previously occupied by the balance boiler, making it possible to install a larger bathtub.
Installing a hole-in-one water heater allows for relatively short construction time and lower costs compared to other replacement options.
The extra space gained from removing the balance boiler also contributes to a more relaxing and satisfying bathing experience.
Costs and Construction Time for Replacement and Renovation
While the basic lifespan of a balance boiler is considered to be 10 years, many units installed in older properties have been in use far longer without replacement.
If you are considering replacing or renovating a balance boiler, how much should you expect to spend, and how long will the work take?
Here we explain the costs and construction timelines for several common scenarios.
Replacing with a New Balance Boiler
Replacing a balance boiler with another balance boiler is common in properties such as housing complexes.
If the property originally had a balance boiler installed, a like-for-like replacement is not unusual.
Even compared to older models, newer balance boilers offer improvements such as greater energy efficiency and reduced scale buildup.
As for the cost of replacing one balance boiler with another, it is relatively affordable — approximately 150,000 yen including installation.
In some cases, the work can be completed within a single day.
Older rental properties in particular tend to still be equipped with balance boilers, and there are cases where the landlord only permits a like-for-like balance boiler replacement.
Replacing with a Hole-in-One Water Heater
A hole-in-one water heater can be installed in the wall opening originally used for the balance boiler's intake and exhaust.
By fitting the heater into the existing wall opening, the space previously occupied by the balance boiler becomes usable.
The bathtub can be replaced with a larger model, and the construction work typically takes about one day.
The total cost including installation is approximately 200,000 to 250,000 yen.
Replacing with a Gas Bath Water Heater
Gas bath water heaters are common in detached homes.
A gas bath water heater can be installed if there is a suitable location outside the bathroom for the unit.
Since the heater is mounted on the exterior, there is no need to allocate space inside the bathroom for it.
The existing intake and exhaust openings can also be used for the pipes, so extensive construction work is generally not required.
A gas bath water heater can supply hot water for bathing as well as enable reheating with the press of a button.
Switching from a balance boiler to a gas bath water heater may therefore come as a pleasant surprise in terms of ease of use.
The cost of switching to a gas bath water heater is approximately 200,000 to 300,000 yen including installation.
Renovating to a Unit Bathroom
For those who are not concerned about budget, renovating to a unit bathroom is recommended.
The balance boiler can be removed and the entire bathroom can be renovated.
Since balance boilers are installed inside the bathroom, older rental properties and housing complexes may still have tiled bathrooms.
Replacing with a unit bathroom integrates all components into a single system.
As a result, benefits such as easier cleaning, reduced risk of water leaks, and better heat retention can be expected.
Unit bathrooms are less affected by outside temperatures, allowing for a comfortable bath even in cold weather.
In rental properties, you may be able to upgrade to a unit bathroom with prior permission from the landlord, though approval is not guaranteed.
It is worth raising the question when the balance boiler breaks down to see whether renovation is possible.
Key Considerations for Repair, Replacement, and Renovation
If your balance boiler breaks down, which option should you choose — repair, replacement, or renovation?
Here we also introduce some important points to keep in mind.
Consulting the Landlord Is Essential for Rental Properties
If a balance boiler in a rental property develops a problem, consult your landlord first.
In a rental property, ownership lies with the landlord or property management company, and the decision of whether to repair or renovate is made by the landlord or management company.
While it is not always clear what type of hot water system will be chosen, the decision ultimately rests with the landlord, so consulting them first is the best course of action.
Replacement May Be Cheaper Than Repair
Common symptoms of a balance boiler malfunction include difficulty igniting, inconsistent water temperature, a popping sound at startup, and unusual odors or noises.
A specialist will need to inspect the unit to identify the cause, but in some cases of failure, replacement can actually be more cost-effective than repair.
While some issues can be resolved with minor parts replacement, if a unit nearing the end of its service life is experiencing multiple problems, replacing the entire unit may resolve all issues at a lower total cost than repeated repairs.
With this in mind, consider whether repair or replacement is the more appropriate choice in light of the unit's age and condition.
DIY Repair or Replacement Is Not Permitted
Those who are skilled at DIY may think that repairing or replacing a balance boiler themselves is straightforward, but balance boiler work requires qualifications such as a gas equipment technician license or a gas appliance installation specialist certification.
In particular, the gas equipment technician license is a national qualification, and performing this work without the appropriate license is extremely dangerous.
In a rental property, the management company or landlord may need to arrange and cover the cost of repairs or replacement when equipment malfunctions.
However, balance boilers are classified as gas appliances, and work on them requires a gas flexible pipe connection work supervisor license, as well as the technical skill to seal openings against moisture and other environmental factors.
Improper DIY work can result in serious malfunctions or accidents, so under no circumstances should you attempt to repair or replace a balance boiler yourself.
How to Choose a Renovation Contractor
If you decide to renovate following a balance boiler breakdown, you may be unsure which contractor to hire.
Here we explain how to go about selecting a renovation contractor.
Verify That Qualified Personnel Are on Staff
If you are considering repairs or renovation involving a balance boiler, you may not know where to turn or who handles this type of work.
The first thing to check is whether the contractor has staff who hold the required professional qualifications.
Regulations require that balance boiler renovation work be carried out by qualified individuals who hold the relevant licenses for installing and replacing hot water supply systems, gas equipment, and plumbing.
Unauthorized repairs by unqualified individuals may be illegal and carry the risk of explosions or gas leaks.
Since accidents can cause serious harm to those nearby, always engage a contractor whose staff hold the following qualifications.
【Required Qualifications】
· Liquefied Petroleum Gas Equipment Technician (national qualification)
· Gas Flexible Pipe Connection Work Supervisor
· Gas Appliance Installation Work Supervisor
· Gas Appliance Installation Specialist
· Water Supply Equipment Work Chief Technician
· Simple Interior Pipe Installation Technician
· TES Work Technician
Compare Multiple Contractors
When comparing renovation contractors, be sure to compare the scope of work and the associated costs clearly.
For renovation work in particular, asking for an estimated construction timeline in addition to the cost will give you greater peace of mind.
For example, renovating from a balance boiler to a hole-in-one water heater involves embedding the unit into the bathroom wall, which allows the bathroom and bathtub to be made larger than with a balance boiler.
Furthermore, the ability to control temperature and fill the bath via a panel — features not available with a balance boiler — makes it significantly more convenient.
Since the existing intake and exhaust openings from the balance boiler can be reused, no new holes need to be made in the wall.
The estimated cost of renovating from a balance boiler to a hole-in-one water heater — including the boiler unit, bathtub, faucet fittings, and installation — is approximately 320,000 to 350,000 yen.
If you purchase from the installation company directly, the cost may be lower, so compare quotes with and without the purchase included.
Also, an important point to keep in mind when comparing multiple contractors is what is involved if a unit bathroom replacement is being considered.
Unlike replacing a balance boiler with a hole-in-one water heater, installing a unit bathroom is not a straightforward construction project.
A unit bathroom is assembled on-site, with components such as the ceiling, floor, walls, and bathtub installed from the top down.
There are also unit bathrooms with an attached vanity unit, as well as three-piece sets that include a toilet, so compare options based on the type you require.
Many unit bathroom models are highly modern, offering ease of cleaning, airtightness, and strong insulation.
Barrier-free and high-functionality designs are also available.
With this in mind, determine which grade of unit bathroom you need, confirm the estimated construction timeline, and clarify what is included in the set before making comparisons.
Renovation costs for a unit bathroom start at approximately 500,000 yen, with installation costs starting at approximately 300,000 yen.
Request Free Estimates
When comparing multiple contractors, use the free estimates provided to make your decision.
Costs, response times, and the level of service can vary significantly between contractors.
Some may charge above-market rates, lack the necessary qualifications, or have limited experience.
In such cases, work may not be carried out properly and issues may arise later.
However, by obtaining free estimates, you can assess not only the scope of work and construction timeline, but also whether the contractor employs qualified personnel, whether the pricing is fair, and what services are included.
Be sure to compare estimates from multiple companies before any work begins.
Summary
A balance boiler is a type of water heater that was commonly installed in housing complexes and similar properties.
Equipped with an air intake and an exhaust port, it draws in bathwater, heats it, and returns it to the tub.
While balance boilers were once the standard, they are now declining in number, and an increasing number of homes are being renovated to unit bathrooms.
Balance boilers do offer advantages such as the ability to heat water during power outages, but their limited water flow, difficulty of cleaning, and a service life of around 10 years are notable drawbacks.
This often leads to the question of whether to replace or renovate — and in rental properties, like-for-like replacement with a new balance boiler may be the only option.
Today's unit bathrooms offer a wide range of features and make better use of bathroom space.
If you are considering upgrading your bathtub at home, obtain estimates from multiple contractors before any work begins, and compare costs, construction timelines, and whether qualified personnel are available.
