Jan. 06, 2025
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What size electric boiler do I need? This is a common question. It may arise when considering a new property or replacing existing gas or oil boilers. The following guide will walk you through the process and key factors to consider when selecting the right size boiler. We offer a full range of electric boilers, including electric system boilers for central heating. This covers underfloor heating and hot water needs, or radiators and domestic hot water via an indirect cylinder, or just electric central heating alone. If you are searching for a "what size electric boiler do I need calculator," keep reading.
The first step in choosing the correct electric heating boiler for a wet heating system is determining the heating load, expressed as your kW requirement. It doesn't matter if you use radiators or an underfloor heating system; the heating load remains the same!
Here is a quick reference chart for properties built after the 1970s, which have a standard ceiling height of 2.7 meters and an insulation value (U value) of 0.3, in line with building standards from the 1970s onward.
You can approach this in a couple of ways:
Power Output of Boiler | Heating Floor Area
As a general rule, for properties built after the 1970s, you should allocate 1.5 kW for each radiator in your home. For instance, if you have eight radiators, you should select a 12kW electric boiler. This rule may vary depending on ceiling height, type of glazing (single or double), and the effectiveness of your property's insulation.
While these guidelines provide a good starting point, it’s wise to verify with a heating engineer to avoid costly errors.
If you have an older property built prior to the 1970s, like a Victorian home or one with different construction methods (e.g., stone or wood), you may need to follow different recommendations:
You can calculate the heat load yourself using the following website. It will determine the required heating load for your home or flat by inputting all your rooms into the calculator and aggregating the total kW needed.
To find the Heat Loss calculator, click here.
2. Consult a plumber or professional heating engineer—they can perform a heat loss calculation for your property and carry out the boiler installation.
Once you have your required output, please visit our dedicated webpages on the appropriate boiler you need:
Combi boilers deliver both heating and hot water in one unit, typically without the need for a hot water cylinder. Nonetheless, conditions regarding available Amps may apply; refer to the above webpage for more details.
The electric boiler sizing process mirrors that of gas and oil boilers. The insulation level of your property is crucial. Higher insulation reduces the required output of the electric central heating system, and vice versa. Since electric boilers produce a kW output, they function similarly to gas or oil boilers, powered by electricity.
To estimate annual running costs, check your existing energy bill for annual heat use, represented in kilowatt-hours (kWh). Multiply your kWh by your electricity tariff to determine your annual electric heating running costs. You may discover that the amount of kWh used by your electric boiler is less than that of your gas or oil boiler due to its higher efficiency.
Obtain your last year's gas bills to determine the kWh used by the boiler, then deduct at least 10% since boilers typically achieve a maximum efficiency of around 90% (electric boilers are 100% efficient). For more insight on Gross vs. Nett efficiency of boilers, you can explore further.
For example, if you've consumed 1,500 kWh of gas and your boiler efficiency is 90%, your calculation would be:
1,500 x 90% = 1,350 kWh
If the boiler effectively operates at 63% efficiency, then:
1,500 x 63% = 945 kWh
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After obtaining this figure, multiply by the electricity price per kWh since electric boilers operate at 100% energy efficiency, allowing for accurate comparison of running costs based on the same usage data as gas or oil boilers.
Similarly, the same principles regarding efficiency apply, but kerosene is usually sold by the litre. Consider the litres purchased or consumed annually in your home.
Each litre of kerosene contains 10.35 kWh of thermal energy. For instance, if you used 500 litres, the energy consumption would be:
500 x 10.35 kWh = 5,175 kWh
Multiplying this by efficiency, say 90% (assuming it’s a condensing oil boiler), gives:
5,175 x 90% = 4,657.50 kWh
Again, multiply this by the price you pay for electricity per kWh to find out the annual cost compared to an oil boiler.
The maximum electric central heating boiler or electric combi boiler that can operate on a single-phase 240-volt supply is 15kW. Electric boilers are typically limited by the maximum amps available in a property, usually 100 Amps for UK residences.
You will need the same size as required for a radiator system, as a "heat loss" is as it is called. Please refer to the "what size electric boiler do I need calculator" on this webpage.
No, electric boilers are available with outputs up to 500kW, so we can cater to any boiler size you might require. The limiting factor will be the amps needed to power the electric boiler. Beyond 15kW output, a 3-Phase electrical supply is necessary.
We hope that the above guidance on "what size electric boiler do I need" helps in determining the size you require for heating, typically referred to as an electric system boiler (including both underfloor and radiator heating). These electric boilers can also be linked to cylinders for heating domestic hot water in your home.
Keep in mind that installation costs for electric boilers are generally lower, as installers do not need to be gas safe registered or OFTEC registered (for oil) as required for gas or oil boiler installations.
Please get in touch with us for your electric boiler costs, whether you need an electric system boiler coupled with a hot water cylinder for your domestic hot water demands.
Generally, electric boilers are more cost-effective than equivalently sized gas or oil boilers.
Electric boilers have traditionally been favored in off-grid areas without mains gas. However, with rising oil prices and a collective desire to reduce fossil fuel reliance, electric heating systems offer a realistic alternative.
The ideal time to design and install any heating system is during construction. Nonetheless, switching from a gas boiler to an electric one is a relatively straightforward process. This is due largely to the simplicity of the system and the significantly enhanced safety of electric boilers.
Most complications arise from the removal of your old system. A gas boiler requires removal by a gas safe heating engineer, ensuring the gas line is capped off safely. For oil systems, the oil feed and tank must also be safely disposed of.
Post-removal of a gas or oil boiler, the flue must also be taken out, which is necessary for venting combustion gases externally. The location of your boiler may leave holes in external walls or ceilings that need to be patched.
If your boiler was manufactured and installed after the 1990s, it likely has a condensation pipe running through the wall to the outside, transferring wastewater to the sewer—this needs removal, too!
Safely dispose of your old boiler and tanks by contacting your local council or visiting their website to ensure compliance with relevant local regulations.
Once the old system is out, installing the new boiler is relatively simple but requires some considerations.
The key consideration for an electric boiler is its power supply. ThermoSphere electric boilers up to 12kW can connect to a standard 230V single-phase supply. For larger outputs (18 to 24kW), a 400V three-phase supply is needed, which is typically found in larger domestic and commercial properties in the UK.
Your boiler must connect to a dedicated and appropriately sized circuit breaker back at your distribution board using the correct cable type and size. An isolation switch should be installed next to the boiler for easy and safe disconnection from the electrical supply during maintenance.
It’s best to have a competent electrician install the electric boiler power supply. They will specify and install the correct size breaker in your distribution board using the proper cable.
The plumbing connections for an electric boiler resemble those for a gas or oil boiler, though there are fewer pipes since there is no fuel supply. Thus, there are no gas or oil lines to manage, flues to install, or condensate pipes. For electric flow or system boilers, you only need to connect a cold input (return) and a hot output (flow) to your plumbing system. Electric combi boilers include connections for the domestic hot water plumbing circuit as well. These water connections are similar to those of gas or oil boilers, but you may need to adjust the pipework near the boiler for proper fitment.
Unlike a heat pump, upgrading all your pipes and radiators isn't necessary when switching to an electric boiler. You can retain everything except the boiler, thereby avoiding hidden costs. Provided the heating circuit remains unchanged and you’re not upgrading to a higher output boiler, any existing expansion vessels can be retained as long as they function correctly.
ThermoSphere electric boilers come with wiring inputs for central heating thermostats. These consist of a pair of volt-free contacts compatible with most central heating controls and wiring centers available in the UK market. Consequently, changing your boiler doesn’t necessitate updates to existing thermostats and controls!
The size or output of your boiler determines the size of the electrical power supply it requires. To ascertain which boiler size to purchase, you need to understand the energy demand of your heating system. One option is to check the output of your existing boiler and select a comparable electric model. For instance, if you have a 12kW gas boiler, you could opt for a 12kW electric boiler for the same demand.
However, verifying your required heat output before finalizing a new boiler purchase is advisable. Many boilers are often over-specified, leading to an installation that is excessively large for the property, potentially reducing efficiency. In such cases, a smaller, less powerful boiler may be more economically viable, requiring less energy while maintaining the same comfort levels.
The standard guideline utilized by heating system designers is to allocate 1.5kW of boiler output per radiator for a heating-only boiler. Applying this rule, if you have eight radiators, a 12kW boiler would suffice. However, note that some radiators may be considerably larger or used at varying times. Therefore, it is prudent to evaluate whether you truly need 1.5kW per radiator. A small landing radiator or bathroom towel rail may only necessitate 500W or less, allowing you to reduce the overall required boiler output, leading to cost savings.
For boilers intended to provide hot water for heating and showers, the common thought is to add 3kW to the boiler's required output, considered a failsafe, yet this is usually unnecessary, even for an electric combi boiler.
This is because a boiler only heats water for heating or hot water at any one time. Thus, if you determine you need 9kW for heating, this amount is more than sufficient to warm the relatively small volume of water moving through the coil in your hot water storage cylinder. Consequently, a 9kW boiler suffices without overcompensating with a 12kW model, which would only incur higher running costs and installation expenses.
To accurately specify the correct boiler size, you should have an energy assessor visit your home. They will provide heat loss calculations and determine required heating output. While this method entails a cost, it ensures that you do not over-specify your boiler, preventing unnecessary energy expenditure.
In summary, transitioning from an old gas or oil-fired boiler to a new zero-emission electric boiler is quite straightforward. Here’s a checklist of the primary considerations:
Complete this short form to receive an electric boiler quote along with the correct specifications for your property.
To discuss electric boilers for larger projects, please call one of our team members at 019.
Our company is the world's best 12kw Electric Steam Boiler (ko, nl, pt). We are your one-stop shop for all electric boiler needs, and our staff are highly specialized to assist you in finding the right product.
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