Electric or water underfloor heating? A comparison of comfort and efficiency

Electric underfloor heating, often referred to as electric floor heating, is a heating system that uses electric heating elements installed beneath the floor surface to warm a room. This system provides a comfortable and evenly distributed heat from the ground up, making it a popular choice for new builds and renovations.

How does electric underfloor heating work?

Electric underfloor heating uses electrical resistance to generate heat, radiating upwards through the floor to warm the room. Several elements are needed to make this system work:

• Heating elements: These are electric cables, mats, or films installed beneath the floor. When connected to the electrical system, they heat up as current flows through them, generating warmth that radiates through the flooring material.
• Thermostat & control: The system is controlled by a thermostat, which allows users to set and regulate the desired temperature. Modern systems often feature programmable or smart thermostats, enabling efficient energy use by adjusting heating schedules according to room occupancy or external conditions.
• Heat distribution: The generated heat is transferred directly to the floor, radiating evenly across the room. The system primarily uses radiant heating, providing consistent warmth from the ground up, which leads to a comfortable and uniform room temperature.
• Automatic shutoff: When turned on, the thermostat activates the electrical current, causing the heating elements to generate heat. Once the set temperature is reached, the thermostat automatically shuts off the system to maintain the desired warmth. The floor gradually cools down after the system is turned off, ensuring continued comfort.

Advantages of an electric underfloor heating system:

1. Ease of installation: Electric underfloor heating is relatively easy and quick to install, especially when using heating mats or films, making it ideal for retrofitting existing homes. The thin profile of the heating elements means that the system doesn't significantly raise the floor height, which is beneficial in renovations.
2. Quick warm-up time: Electric systems heat up faster than water-based systems, providing quick warmth and are particularly useful in bathrooms and kitchens.
3. Zoned heating control: Each room can have its thermostat, allowing for precise temperature control in different areas and improving energy efficiency and comfort.
4. Low maintenance: Electric systems have fewer moving parts than hydronic systems, resulting in less maintenance and fewer potential repair issues over time.

Disadvantages of an electric underfloor heating system:

1. Higher operating costs: Running costs can be higher than water-based systems, especially in areas with high electricity rates, making them less economical.
2. Not ideal for large areas: While effective in small to medium-sized rooms, electric underfloor heating may not be cost-effective for heating large spaces due to higher energy consumption.
3. Flooring compatibility: Certain types of flooring, such as thick carpets, can insulate the heat, reducing the system’s efficiency. Careful consideration of flooring materials is necessary to ensure optimal performance.
4. Upfront costs: Although electrical systems are easier to install, upgrading electrical systems in some homes can increase the initial installation cost.

Best suited for?

Electric underfloor heating is best suited for smaller rooms and renovations. It offers quick warmth and ease of installation with minimal impact on floor height. It is ideal for spaces where rapid heating and precise temperature control are needed, though it may be less economical for large areas due to higher operating costs.

Underfloor water heating, also known as hydronic underfloor heating, is a system that uses warm water circulated through a network of pipes laid beneath the floor to heat a space. This type of heating is particularly energy-efficient and provides consistent, even warmth across the room.

How does water underfloor heating work?

Water underfloor heating works with three different components:

1. Heat source: The water is heated by a boiler, heat pump, or solar thermal system. The water temperature is usually kept between 30°C and 50°C, much lower than the temperature required for traditional radiators.
2. Pipes: The heated water is pumped through a series of flexible pipes arranged in loops beneath the floor surface. These pipes are embedded in a screed or laid on top of insulation boards, ensuring that the heat is directed upwards into the room rather than being lost into the ground.
3. Heat distribution: As the warm water flows through the pipes, it radiates heat through the floor surface, warming the room from the ground up. This creates a comfortable and even heat distribution without the hot and cold spots that can occur with conventional radiators.

Advantages of underfloor water heating:

1. Energy efficiency: Hydronic underfloor heating systems typically operate at lower temperatures (30°C to 50°C) than traditional radiators, making them more energy-efficient. These systems work well with renewable energy sources such as heat pumps and solar thermal systems, reducing energy consumption and carbon footprint.
2. Silent operation: Underfloor water heating systems operate quietly, without the noise associated with conventional radiators or forced-air systems. This creates a more peaceful and comfortable living environment, enhancing the overall experience of the space.
3. Scalability for larger areas: Underfloor water heating systems are more suitable for heating large areas, such as entire homes or commercial spaces, because they can efficiently distribute heat over extensive surfaces using a centralised boiler or heat pump. In contrast, electric underfloor heating is generally more suited for smaller spaces, as its efficiency can decrease in larger installations due to higher energy consumption and operational costs.
4. Long-term cost savings: Due to its efficiency, underfloor water heating can lead to lower energy bills over time, especially in larger spaces or well-insulated homes. The components, particularly the pipes, are durable and often come with long warranties, reducing the need for frequent replacements.

Disadvantages of underfloor water heating:

1. High installation costs: Installing a hydronic system is generally more expensive than electric underfloor heating or traditional radiators, particularly in existing buildings where floors may need to be lifted or reinforced. The installation process is more complex and labour-intensive, requiring skilled professionals, which adds to the cost.
2. Slow response time: Underfloor water heating systems can take longer to warm up than electric underfloor systems, making them less responsive to sudden temperature changes. These systems often rely on smart thermostats or advanced controls to maintain comfort and efficiency, which can add to the initial setup costs.
3. Maintenance and repairs: Since the pipes are embedded beneath the floor, any issues that arise (e.g., leaks) can be more difficult and costly to access and repair. Repairs may require lifting the flooring, which can be disruptive and expensive.
4. Initial warm-up time: It takes time to heat the entire floor mass before the room temperature rises, so it’s not ideal for spaces that need quick heating on demand.

Best suited for?

Water underfloor heating, ideal for new builds, large spaces, and high-performance homes in New Zealand, offers efficient and even heat distribution while pairing well with renewable energy sources. Although it involves a higher initial cost and complex installation, it provides long-term cost savings, enhanced comfort, and aesthetic flexibility for homeowners prioritising sustainability and consistent warmth.

Related article: The benefits of bespoke hydronic heating design

Underfloor heating provides an efficient and comfortable way to heat your home, with options ranging from electric to water-based systems. Installation generally takes two to three days, depending on the system's complexity and the heated area's size. It's important to understand the general gist of the installation process for each type of system, as both electric and water-based underfloor heating have distinct requirements and benefits, influencing the time, cost, and overall suitability for your project.

Electric underfloor heating

Electric underfloor heating is installed by laying heating cables or pre-fabricated mats beneath the floor, which connect to the mains electricity supply. This process is usually quick and less disruptive, making it ideal for new construction and retrofitting. Proper insulation is crucial to ensure energy efficiency and prevent heat loss.

• Average installation time: 1 to 2 days

• Installation cost: $87 per square metre

Water underfloor heating

Water underfloor heating involves installing pipes beneath the floor, which circulate warm water from a boiler or heat pump. The system is typically installed during new builds or major renovations, as it requires access to the subfloor and is more complex than electric systems. Proper insulation is essential to maximise efficiency and prevent heat loss, making it a long-term, energy-efficient solution for heating large areas.

• Average installation time: 3 to 5 days

• Installation cost: $175 per square metre

Related article: The complete guide to underfloor heating in New Zealand 

Warmer Kiwi Homes

The Warmer Kiwi Homes programme offers up to 90% funding for installing underfloor heating in eligible homes. To qualify, you must meet specific income and home condition criteria. Apply by visiting the Warmer Kiwi Homes website or contacting them directly, where you can submit your details and receive guidance on the next steps for securing the grant.

To make an informed decision, it's essential to understand the costs associated with electric and water underfloor heating systems. The running costs for these systems differ based on their energy sources and operation. 

Electric underfloor heating

Electric underfloor heating often isn't a whole-house solution, as many people use this option for rooms with cold floors, like tiled bathrooms or kitchens with hardwood floors. Nevertheless, to estimate the running cost for your home, begin by calculating the power consumption. Multiply the power rating of the heating system by the heated area, then divide by 1,000 to convert it to kilowatts. Next, determine the daily cost by multiplying the power consumption by the hours the heating is used daily and your electricity rate. Finally, calculate the annual fee by multiplying the daily cost by the days you use the heating each year.

Assume: 

• Watts per metre: 100 W/m²
• Heated area 1: Bathroom 10m² (average size)
• Heated area 2: Kitchen 15m² (average size)
• Daily running time: 4 hours (2 hours morning and 2 hours evening)
• Cost of electricity: $0.33/kWh

Example equation:

1. 100W/m² × 25m² / 1000 = 2.5kW power consumption
2. 2.5kW ​× 4 hours × $0.33/kWh = $3.30 daily cost
3. $3.30 day x 180 days = $594 annual cost (seasonal use)

Water underfloor heating

Water underfloor heating, on the other hand, is typically used as a whole-house solution, providing consistent warmth across an entire home. A good way to estimate the monthly running cost for your utility bill is that it will be $1.00 - $1.50 per square metre during a winter month. Then multiply that by the square metres of your home.

Assume:

• Cost: $1.25/m² 
• Average New Zealand home: 150m² 

Example:

1. $1.25 x 150m²  x 6 months = $1,125 annual cost (seasonal use)

This cost covers underfloor heating for an entire house, compared to our figure used for electric underfloor heating, which only applies to the kitchen and bathroom.

• Room size: Electric for small/medium rooms; water for larger areas.
• Installation: Electric for easy retrofits; water for new builds.
• Flooring compatibility: Check suitability with flooring type.
• Heating speed: Electric warms up faster; water provides consistent heat.
• Energy source: Electric is costlier to run; water works well with renewables.
• Costs: Electric has lower upfront costs; water offers long-term savings.
• Maintenance: Electric is low maintenance; water requires more upkeep.
• Sustainability: Water systems are more energy efficient.
• Control: Electric offers precise zoning; water has slower response times.

Choosing between electric and water underfloor heating systems in New Zealand depends on various factors, including your home's size, energy sources, and heating needs. Electric underfloor heating is ideal for smaller rooms and renovations, offering quick installation and precise temperature control, but it may have higher running costs and environmental impact. On the other hand, water underfloor heating, while more costly and complex to install, provides efficient and even warmth over larger areas and pairs well with renewable energy sources, offering long-term savings and environmental benefits. Understanding these factors will help you determine the best system for your specific requirements and budget.

Related article: The great debate: deciding between a wood-burning or gas fireplace for your home