Last Updated: October 14, 2026
An under sink water heater is a compact electric unit installed beneath or near a sink to provide hot water directly at the tap. Available as small storage or instantaneous models, it is ideal for kitchens, offices and utility rooms where hot water is needed without a long wait. In Ireland, the best option depends on water pressure, usage, electrical supply and installation requirements.
At Dublin Plumber 24hrs, we provide under sink water heater installation and replacement across Dublin, with over 24 years of plumbing experience and a 12-month workmanship warranty on eligible work (T&Cs apply).
Under sink water heaters are particularly useful in properties where the main hot water supply is far from the tap or where only a small amount of hot water is needed. They are commonly installed in homes, offices, shops and utility areas. Storage models keep a limited amount of hot water ready for use, while instantaneous heaters heat water as it flows through the unit.
Choosing the right system involves more than selecting a tank size. The available cupboard space, existing pipework, water pressure, tap compatibility and electrical requirements must all be considered. At Dublin Plumber 24hrs, we help homeowners and businesses choose suitable solutions and provide a quotation before installation begins.
What Is an Under Sink Water Heater?
An under sink water heater is a compact appliance designed to provide hot water close to where it is used. Instead of waiting for hot water to travel through long pipework from a central cylinder or boiler, the heater supplies water locally.
This can be particularly useful where the sink is far from the main hot water supply or where installing additional hot water pipework would be inconvenient.
Under sink water heaters are commonly used in:
Kitchens: For washing dishes, cleaning and everyday hot water needs.
Utility rooms: Where a separate hot water supply is useful.
Offices and workplaces: For small kitchenettes and washbasins.
Shops and commercial premises: Where hot water is required at individual sinks.
Garages and garden rooms: Where extending the existing hot water system may be impractical.
Some models store a small amount of heated water, while others heat the water as it flows through the appliance.
Although these heaters are compact, the correct installation is important. Water pressure, pipe connections, electrical requirements and the manufacturer’s instructions must all be considered.
Three Types of Under Sink Water Heaters
Not all under sink water heaters work in the same way. Understanding the differences can help you choose a system that suits your hot water needs.
1. Small Storage Under Sink Water Heaters (5–15 Litres)
Small storage heaters contain an insulated tank that heats and stores a limited amount of hot water.
Common capacities include 5, 10 and 15 litres, although other sizes are available.
These heaters are often suitable for kitchen sinks, office kitchenettes and washbasins where hot water is needed in short periods throughout the day.
Advantages:
Compact design that fits beneath many sinks.
Stored hot water is available when the unit reaches its set temperature.
Suitable for smaller, regular hot water demands.
Different tank sizes are available.
Things to consider:
The stored hot water can run out during extended use.
The tank needs time to reheat after significant use.
Some energy is used to maintain the stored water temperature.
Sufficient cupboard space and access are required.
A 10-litre heater may be suitable for some kitchen or utility sinks, but the correct size depends on how much hot water is used and how frequently.
2. Instantaneous Electric Under Sink Water Heaters
An instantaneous under sink water heater heats water as it passes through the unit rather than storing it in a tank.
These systems are sometimes called tankless or on-demand water heaters.
They can be useful where cupboard space is limited or where hot water is needed occasionally.
Advantages:
No storage tank is required.
No ongoing heat loss from stored hot water.
Compact design.
Hot water is heated when the tap is used.
Things to consider:
Hot water flow depends on the unit’s heating capacity and incoming water temperature.
Higher-powered models may require a dedicated electrical circuit.
Some units are designed for only one outlet.
The available electrical supply must be checked before installation.
An instantaneous heater is not automatically the best choice for every kitchen. Some smaller models may struggle to provide the flow rate or temperature needed for regular dishwashing.
3. Vented and Unvented Under Sink Water Heaters
Another important difference is whether the heater uses a vented or unvented water system.
This classification applies to how the heater handles water pressure, rather than whether it stores or instantly heats water.
Vented under sink water heaters
Vented systems are commonly designed for use with a compatible special tap or outlet arrangement. The tap and heater must be matched according to the manufacturer’s instructions.
They can be suitable for individual sinks where a simple, dedicated hot water supply is required.
Unvented under sink water heaters
Unvented systems are designed to operate under pressure and may supply suitable outlets depending on the model.
They can require additional safety components, such as pressure control and expansion arrangements, depending on the installation and manufacturer’s specifications.
Which type is better?
The best choice depends on the property’s plumbing, available water pressure, tap arrangement and intended use.
A plumber should check these details before recommending a replacement or new installation.
Under Sink Water Heater Prices in Ireland (2026)
The cost of an under sink water heater in Ireland depends on the type of unit, storage capacity, installation requirements and whether an existing heater is being replaced.
It is important to distinguish between the price of the heater itself and the total cost of supplying and fitting it.
A heater advertised online may appear inexpensive, but the product price does not necessarily include plumbing connections, electrical work, safety components or installation labour.
What Affects the Installation Cost?
1. Type and size of heater
A small storage heater and a high-powered instantaneous heater have different installation requirements. Larger or more specialised units may cost more.
2. Replacement or new installation
Replacing an existing heater can be more straightforward when the plumbing and electrical connections are suitable.
A completely new installation may require additional pipework, electrical connections and cupboard alterations.
3. Plumbing and electrical requirements
The installer must check the water supply, pressure and existing connections. Some heaters also require specific electrical protection or a dedicated circuit.
Any electrical work requiring a registered electrical contractor should be carried out by an appropriately registered professional.
4. Additional fittings and safety components
Depending on the model, installation may require compatible taps, isolation valves, pressure-reducing valves, expansion components or other manufacturer-specified fittings.
5. Access and location
A heater installed in an easily accessible cupboard may take less work than one fitted in a restricted space or where existing pipework needs modification.
For more information about our standard call-out charges and hourly rates, see our plumbing prices in Dublin. Under sink water heater installation and replacement costs depend on the work required, and we provide a quotation before starting.
Under Sink Water Heater Supply and Installation Costs
| Type of work | What affects the price |
|---|---|
Heater supply only |
Brand, capacity, heating technology and specifications |
Straightforward replacement | Existing connections, heater compatibility and required fittings |
New installation | New plumbing, electrical requirements and access |
Larger or specialist installation |
Heater capacity, safety components and additional labour |
For an accurate quotation, it is best to confirm whether you need a straightforward replacement or a completely new installation.
At Dublin Plumber 24hrs, we assess the plumbing requirements and provide a quotation before work begins. Our eligible installation workmanship is covered by a 12-month warranty (T&Cs apply), with product warranties provided according to the manufacturer’s terms.
Need an under sink water heater installed or replaced in Dublin? Contact Dublin Plumber 24hrs for a quotation based on your property’s requirements.
Under Sink Water Heater Installation in Dublin
Installing an under sink water heater involves more than simply connecting a unit beneath the kitchen sink. The heater must be suitable for the property’s water supply, electrical connections and intended hot water usage.
At Dublin Plumber 24hrs, we provide plumbing installation and replacement services across West Dublin, South Dublin and Dublin City Centre.
What Happens During Installation?
1. Check the existing plumbing
The first step is to inspect the cold water supply, water pressure, available space and existing pipework. This helps determine which type of heater is suitable.
2. Choose the right heater
The heater should match the customer’s hot water requirements. A small storage unit may be suitable for occasional use, while a different system may be needed for higher demand.
3. Prepare the installation area
The cupboard or installation space must provide suitable access, support and clearance. Any required plumbing alterations are completed before the heater is fitted.
4. Connect the water supply
The heater is connected using suitable fittings and any safety components specified by the manufacturer.
5. Check the electrical requirements
Electric water heaters require an appropriate electrical supply and protection. Where electrical installation or alterations are necessary, the work must be carried out by an appropriately registered electrical contractor.
Electric water heaters must have a suitable electrical supply and protection. Where electrical installation or alterations are required, use a registered electrical contractor. You can find information about registered electrical contractors through Safe Electric Ireland.
6. Test the installation
The completed installation is checked for leaks, correct operation and safe water heating in accordance with the manufacturer’s instructions.
Professional installation helps reduce the risk of leaks, incorrect connections and avoidable problems.
Under Sink Water Heater Replacement – When Should You Replace It?
An existing under sink water heater may eventually develop faults or become less reliable.
Some problems can be repaired, while others make replacement the more practical option.
Signs Your Under Sink Water Heater May Need Replacing
No hot water
If the heater stops producing hot water, the cause could be a faulty thermostat, heating element, electrical supply or another component. A proper assessment is needed before deciding whether replacement is necessary.
Water leaking from the heater
Leaks may come from plumbing connections, valves or the heater itself. A leaking connection may be repairable, but a damaged or corroded storage tank often requires replacement.
Water is not hot enough
A faulty thermostat, heating element or incorrectly sized heater can affect water temperature.
Frequent breakdowns
If the heater requires repeated repairs, replacing it may be more economical than continuing to repair an ageing unit.
Visible corrosion or damage
Rust, damaged fittings or deterioration around the unit should be investigated before further use.
Repair or Replace – Which Is Better?
The decision depends on the age of the heater, the nature of the fault, the availability of replacement parts and the cost of repair.
A relatively new heater with a minor fault may be worth repairing. However, an older unit with a leaking tank or repeated electrical problems may be better replaced.
Before replacing an existing heater, it is important to check whether the new model is compatible with the plumbing, tap arrangement and electrical supply.
If your existing unit is leaking, no longer heating properly or repeatedly breaking down, our water heater replacement service can help you find a suitable solution.
Are Under Sink Water Heaters Expensive to Run?
The running cost of an under sink water heater depends on its power rating, how often hot water is used and the electricity tariff.
Small storage heaters use electricity to heat water in a tank. They may also use some energy to maintain the stored water temperature.
Instantaneous heaters use electricity when hot water is being drawn, but some models require a higher electrical power input.
Choosing the right heater size and using hot water efficiently can help manage electricity costs. For more information about energy efficiency and saving energy at home, visit the Sustainable Energy Authority of Ireland (SEAI).
What Affects Electricity Consumption?
Heater capacity: Larger storage tanks generally require more energy to heat a full tank of cold water.
Hot water usage: Frequent use increases energy consumption.
Thermostat settings: Higher water temperatures can increase energy use.
Insulation: Better-insulated storage heaters generally lose less heat while standing.
Electricity prices: Running costs depend on your electricity supplier and tariff.
How to Reduce Running Costs
Choose a heater that matches your actual hot water needs rather than installing a unit that is unnecessarily large.
Avoid leaving hot taps running longer than needed, and have faulty or dripping taps repaired.
For storage heaters, use the manufacturer’s recommended temperature settings and operating instructions. Avoid unsafe temperature reductions that could increase bacterial risks.
An under sink heater can be convenient when hot water is required at a sink far from the main hot water supply. However, it is not automatically cheaper to run than a central hot water system.
Common Under Sink Water Heater Problems
Like other plumbing and heating appliances, under sink water heaters can develop faults over time.
1. No Hot Water
Possible causes include an electrical supply problem, faulty thermostat or failed heating element.
If the heater repeatedly trips an electrical circuit, stop using it and arrange a professional inspection.
2. Water Leaking Under the Sink
Leaks may develop around pipe connections, valves or the heater.
If water is leaking near electrical connections, avoid touching the appliance or wet electrical fittings. Have the supply safely isolated and arrange professional assistance.
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3. Water Temperature Keeps Changing
Inconsistent hot water may be caused by thermostat faults, flow-rate problems or a heater that is unsuitable for the demand.
4. Low Hot Water Pressure
Low flow can result from blocked fittings, restrictions in the supply or an unsuitable heater and tap arrangement.
5. Unusual Noises
Some noises can be associated with heating and expansion. Persistent or unusual sounds may indicate a problem that needs checking.
6. Heater Takes Too Long to Reheat
Storage heaters need time to replenish their hot water supply. Excessively long reheating times may indicate a fault or a unit that is too small for the intended use.
Important: Do not open or attempt electrical repairs on a water heater unless you are appropriately qualified. Electrical and pressurised hot water systems can present serious safety risks.
Under Sink Water Heater Warranty – Workmanship and Manufacturer Cover
When having an under sink water heater installed, it is important to understand the difference between the installation warranty and the product warranty.
12-Month Workmanship Warranty
At Dublin Plumber 24hrs, eligible under sink water heater installation and replacement work comes with a 12-month workmanship warranty.
This covers qualifying installation workmanship under our warranty terms and conditions.
Manufacturer's Product Warranty
The heater itself is covered according to the manufacturer’s warranty period, terms and conditions.
Product warranty periods and exclusions vary between manufacturers and models. The manufacturer’s warranty is separate from our workmanship warranty.
T&Cs apply. Contact us for full warranty details before installation.
Why Choose Dublin Plumber 24hrs for Under Sink Water Heater Installation?
Choosing the right heater is important, but correct installation matters just as much.
Dublin Plumber 24hrs provides plumbing services for homes and businesses throughout Dublin.
With over 24 years of plumbing experience, we help customers with new installations, replacement heaters and plumbing problems.
Our service includes:
Professional plumbing installation and replacement.
Advice on suitable heater types and capacities.
Assessment of existing plumbing connections.
Upfront quotations before work begins.
A 12-month workmanship warranty on eligible work, with T&Cs applying.
Manufacturer’s warranty according to the selected product’s terms.
Coverage across North Dublin, South Dublin and Dublin City Centre.
Whether you need to replace a leaking heater or install a new hot water supply beneath your sink, we can assess the plumbing requirements and explain the available options.
Need an under sink water heater installed or replaced in Dublin? Contact Dublin Plumber 24hrs for a quotation.
Need an Under Sink Water Heater Installed or Replaced in Dublin?
Whether you’re replacing an old heater or installing a new one, Dublin Plumber 24hrs can help.
With over 24 years of plumbing experience, we offer professional installation, upfront quotations and a 12-month workmanship warranty on eligible work (T&Cs apply). Product warranties apply according to the manufacturer’s terms.
Frequently Asked Questions About Under Sink Water Heaters
1. Are under sink water heaters any good?
Yes. Under sink water heaters are a practical option for kitchens, utility rooms, offices and other areas where hot water is needed close to the tap. They can reduce the wait for hot water from a distant central system. However, the right choice depends on your hot water usage, available space and installation requirements.
2. Can you put a water heater under the sink?
Yes. Compact water heaters are specifically designed for installation beneath or near a sink. Common options include small storage heaters and instantaneous electric models. The cupboard must have suitable space, clearances specified by the manufacturer, safe electrical connections and appropriate plumbing fittings.
3. What are the pros and cons of an under sink hot water heater?
The main advantages are convenient hot water, compact size and reduced waiting time at the tap. Disadvantages can include limited hot water capacity in storage models, electricity running costs and installation requirements. Some instantaneous heaters also need a higher-capacity electrical supply.
4. How long do under sink water heaters last?
Many under sink water heaters can last around 8–15 years, although their actual lifespan depends on the model, water quality, usage and maintenance. Some may last longer, while others need replacing sooner. Leaks, corrosion, repeated faults or unreliable heating can indicate that replacement is necessary.
5. What is the best under sink water heater?
The best under sink water heater depends on how much hot water you need and where it will be installed. A small storage heater may suit a kitchen or office sink, while an instantaneous model may work better for occasional use where the electrical supply is suitable. Check capacity, water pressure, energy use, safety requirements and warranty before choosing.
6. Are under sink water heaters expensive to run?
Running costs depend on electricity prices, heater size and how frequently hot water is used. Storage heaters consume energy to heat water and may use additional electricity to maintain its temperature. Instantaneous heaters heat water on demand. Choosing the correct size and avoiding unnecessary hot water use can help manage costs.
7. Why do some plumbers not recommend tankless water heaters?
Tankless water heaters are not unsuitable in every situation, but some models have limitations. Small electric units may provide a lower hot water flow rate, particularly when incoming water is cold. Higher-powered models can also require electrical upgrades. A plumber can help determine whether a storage or instantaneous heater is better for the property.
8. How much does an under sink water heater cost in Ireland?
The cost depends on the heater’s capacity, type and installation requirements. A straightforward replacement may cost less than a completely new installation requiring additional plumbing or electrical work. At Dublin Plumber 24hrs, we provide quotations based on the work required, so you know the agreed price before installation begins.
9. Should I buy an under sink water heater from a plumber?
Buying through a plumbing company can make it easier to choose a heater that suits your existing water supply and installation requirements. You can also purchase a heater separately, but it is worth checking compatibility with your installer before ordering. Product warranties remain subject to the manufacturer’s terms.
10. Does under sink water heater installation come with a warranty?
Yes. Dublin Plumber 24hrs provides a 12-month workmanship warranty on eligible under sink water heater installations and replacements. The water heater and its components are covered separately by the manufacturer’s product warranty, according to the manufacturer’s warranty period and conditions.
T&Cs apply. Contact us for full warranty details and a free quotation.