Guide · electric
Electric combi boilers
No gas, no flue, no RGI, and a running cost about two and a half times gas per unit of heat. What the two kinds are, what they can and can't do for hot water, and where one fits.
An electric combi boiler heats radiators and hot water from electricity instead of gas, with no flue, no gas supply and no RGI. The catch is the running cost: on SEAI's 1 July 2026 comparison, electricity on the typical band was 34.38 cent per kWh against 13.0 cent for natural gas, so the same heat costs roughly two and a half times as much.
It makes sense where there is no gas and no room for a cylinder: an apartment in an all-electric block, a small home, a holiday home. In a family house on the gas network, it doesn't.
What an electric combi is, and the two kinds
The name covers two different machines. Take the Electric Heating Company's range, the brand most quoted for these units in Ireland and the UK (EHC Comet and EHC Mercury, read 29 October 2026):
- A boiler with a built-in cylinder. The EHC Comet is a floor-standing unit with a 9, 12 or 14.4 kW heating element and an integrated 140-litre stainless steel hot water cylinder in one casing. It's a system boiler and cylinder in a cabinet, sold for "domestic properties with no access to mains gas". It needs floor space, and it stores hot water like a cylinder does.
- A true instantaneous combi. The EHC Mercury heats hot water on the way through, like a gas combi. It comes in 12 and 14.4 kW on a single-phase supply and 19 and 26 kW on three phase. The maker's own fittings tell the story: a flow restrictor of 5 litres a minute for the 12 kW model, 6 for 14.4 kW, 8 for 19 kW and 12 for 26 kW, and only the three-phase 19 and 26 kW models are described as suitable for baths.
Why the hot water is the limit
Heating water takes about 1.16 kWh for every 1,000 litres raised by 1 °C. A gas combi can put 25 to 38 kW into the water as it passes: Vaillant's ecoTEC plus combis deliver 10.5 to 15.9 litres a minute at a 35 °C rise (Vaillant technical sheet). A single-phase electric combi has 12 or 14.4 kW to play with, which is why the maker restricts the flow to 5 or 6 litres a minute: that's what the element can heat. A 6-litre-a-minute shower is a trickle by gas standards. The three-phase models do better, but a three-phase supply is unusual in an Irish home.
| Electric combi (single and three phase) | Hot water flow, maker's restrictor |
|---|---|
| 12 kW | 5 litres a minute |
| 14.4 kW | 6 litres a minute |
| 19 kW (three phase) | 8 litres a minute |
| 26 kW (three phase) | 12 litres a minute |
Source: Electric Heating Company, Mercury combi boiler, read 29 October 2026. The Comet, with its built-in 140-litre cylinder, sidesteps the flow problem by storing hot water instead.
What it costs to run
This is the number to look at before anything else. SEAI's comparison for 1 July 2026 gives these delivered prices, including VAT (SEAI Domestic Fuels comparison, read 29 October 2026):
| Electricity, band DD | Natural gas, band D2 | Electricity, night rate | |
|---|---|---|---|
| Delivered, cent per kWh | 34.38c | 13.0c | 15.42c |
| Typical seasonal efficiency (SEAI) | 100% | 85–97% | 100% |
| Useful heat, cent per kWh at 90% | 38.2c | 14.45c | – |
| 10 kWh of heat, about an hour of a small home's heating | €3.44 | €1.44 | €1.54 |
On the CRU's average gas consumption of 11,000 kWh a year (Electric Ireland, citing the CRU), the same heat from a gas combi at 90% costs about €1,589 in gas, and from an electric combi about €3,782 in electricity, both before standing charges. Night rate at 15.42 cent is the one way to bring electric heating costs down, and it only works with storage: the Comet's cylinder, storage heaters, or a battery. An instantaneous electric combi heats water when you open the tap, which is rarely at night.
What it costs to install
No Irish installer we could read on 29 October 2026 publishes an installed price for an electric combi, so we don't give one. What's known about the job: there's no gas work, so no RGI and no completion certificate for gas, but the electrical supply is the whole job. A 12 kW single-phase unit draws over 50 amps, which usually means a dedicated circuit from the consumer unit and a check that the home's supply can carry it; a three-phase unit needs a three-phase supply that most homes don't have. That work must be done by a registered electrician. For comparison, a gas combi swap has a median published price of €2,600 across 12 installers.
Where an electric combi makes sense
- An apartment in an all-electric block, replacing an old electric boiler or storage heaters
- A small home or holiday home with no gas and nowhere for an oil tank
- Somewhere a flue is impossible and a cylinder won't fit
- A home with solar panels and a battery that can cover much of the daytime load
Where it doesn't
Any house on the gas network, and any family house with two or more showers. The running cost settles the first; the flow rate settles the second. If the house has no gas, the grant-aided route is a heat pump, which moves two to four units of heat for each unit of electricity and carries up to €14,500 in SEAI grants for a house: see combi boiler grants. There is no SEAI grant for an electric combi.
Questions to ask before you buy
- Is this an instantaneous combi or a boiler with a built-in cylinder?
- What is the hot water flow rate, in litres a minute, at a 35 °C rise?
- Single phase or three phase, and can my supply carry it?
- What will it cost to run on my tariff, per kWh, against gas?
- Would a heat pump with its grant cost less over ten years?
Questions people ask
How much does an electric combi boiler cost to run?
On SEAI's 1 July 2026 prices, electricity on the typical band was 34.38 cent per kWh against 13.0 cent for gas. For the CRU's average 11,000 kWh of heat a year, that's about €3,782 in electricity against about €1,589 in gas, before standing charges.
Can an electric combi run a shower?
A single-phase 12 or 14.4 kW instantaneous unit is restricted by its maker to 5 or 6 litres a minute, a weak shower. Three-phase 19 and 26 kW models manage 8 and 12 litres a minute. A unit with a built-in cylinder, like the EHC Comet, stores hot water instead.
Does an electric combi need a flue or an RGI?
No flue and no gas work, so no RGI. It needs a registered electrician for a dedicated high-current circuit, and a check that the supply can carry it.
How much does an electric combi cost to install in Ireland?
We found no Irish installer publishing a price on 29 October 2026, so we don't give one. A gas combi swap has a median published price of €2,600.
Is there a grant for an electric combi boiler?
No. SEAI's grants cover heat pumps, insulation, controls, solar and batteries. A heat pump gets up to €14,500 for a house.
Is an electric combi better than storage heaters?
It gives wet central heating with radiators and on-demand hot water, which storage heaters don't. It also costs more to run than night-rate storage heaters, because it uses day-rate electricity when you call for heat.
Sources (4)
Prices and facts on this page were checked against these published pages. We are not connected to these businesses.
- EHC Comet: electric-heatingcompany.co.uk
- EHC Mercury: electric-heatingcompany.co.uk
- Vaillant technical sheet: professional.vaillant.co.uk
- Electric Ireland, citing the CRU: electricireland.ie
Want a fixed price for a new boiler?
Call 087 162 1846 between 8am and 8pm, or leave your number and one RGI-registered installer who covers your county rings you back.