Guide · apartments
Combi boilers for apartments
One bathroom, no attic, no room for a cylinder: the combi's home ground. What decides whether one can go in is the flue, the gas supply and the management company. Here are the rules and the price.
A combi suits most apartments better than any other boiler: one bathroom, no room for a cylinder, and a short flue straight through an outside wall. The things that decide whether one can go in are the flue position, the gas supply and the management company, not the boiler.
Like for like, a combi swap in an apartment is priced the same as in a house: a median €2,600 across 12 installers' published prices, with the middle half at €2,199–€2,800.
Why apartments and combis go together
A combi heats water as you use it, so there's no hot water cylinder and no tank in the attic. In an apartment there is no attic, the hot press is a cupboard somebody wants back, and the hot water demand is usually one bathroom and a kitchen. That's the combi's home ground. Most apartments built in Ireland since the 1990s with gas heating were built with a combi, and a replacement is a like-for-like swap in the same spot.
The Census shows how much of the stock this is. Apartments in purpose-built blocks made up over 20% of the occupied homes built between 2001 and 2010, and 15% of those built since 2016 (CSO Census 2022, Profile 2, read 29 October 2026). The 2001 to 2010 blocks are the ones whose original boilers are now 15 to 25 years old.
Gas or electric: check before you price
Not every apartment has gas. Newer blocks in particular are often all-electric: the Census found nearly half of homes built between 2016 and 2022 used electricity as their main central heating, against 10% of older homes (CSO). If there's no gas meter for the apartment, a gas combi isn't an option without a gas connection to the block, which is rarely practical. The alternative is an electric combi or an electric boiler with a cylinder.
The flue: where the rules bite
A combi's flue has to end outside, and the Building Regulations set minimum distances from the terminal to windows, vents, balconies and neighbouring terminals. In a block, those distances are what decide whether the boiler can stay where it is or has to move. Technical Guidance Document J gives the minimums for a room-sealed, fanned-draught terminal, the type on every modern combi (TGD J 2014, Table 5, read 29 October 2026):
| Terminal position | Minimum distance |
|---|---|
| Directly below an opening window, vent or air brick | 300 mm |
| Below gutters or soil pipes | 75 mm |
| Below eaves | 200 mm |
| Below a balcony or car port roof | 200 mm |
| From an internal or external corner | 300 mm |
| From a surface or boundary facing the terminal | 600 mm |
| From a terminal facing a terminal | 1,200 mm |
| Horizontally from a door, window or vent | 300 mm |
| Vertically from a terminal on the same wall | 1,500 mm |
| From a gas meter or meter cabinet | 300 mm |
Source: Technical Guidance Document J, Heat Producing Appliances, 2014, Table 5, room-sealed fanned-draught column. The distances marked as minimum safety distances in TGD J override any lesser figure from the boiler maker. Installation must follow I.S. 813.
Two of these come up constantly in blocks: 300 mm directly below an opening window or vent, and 1,200 mm from a terminal facing another terminal across a lightwell or courtyard. A balcony above the terminal needs 200 mm. The installer checks all of it on the survey, and if the existing flue position fails, the boiler moves or a plume kit redirects the exhaust. TGD J also asks installers to consider siting a condensing boiler's flue so its plume of wet flue gas doesn't affect the use of the dwelling or neighbouring buildings.
The management company
The outside wall of your apartment is usually common property. A new flue hole, a moved terminal, or scaffolding on a top floor, all need the management company's agreement, and some blocks have rules on where terminals may go. Ask before the installer quotes. A like-for-like swap through the existing flue hole is the easiest case, and usually needs no permission at all.
Sizing a combi for an apartment
Apartments need less heat than houses, but a combi is sized on hot water as much as on radiators. One Dublin installer's own guide puts a small house or flat with up to about 10 radiators at 9–18 kW, from €2,095 plus VAT (gasboiler.ie, read 29 October 2026). For hot water, the maker's flow rate is the figure to compare: Vaillant's ecoTEC plus 825, a 25 kW combi, delivers 10.5 litres a minute at a 35 °C rise (Vaillant technical sheet), enough for one shower. Two showers at once in an apartment is rare, which is why a combi fits.
Mains pressure in a block
A combi runs off the mains, and in a block the water may come from a pumped supply or a roof tank rather than straight from the street. Low pressure on an upper floor means a weak shower. Ask the installer to measure the flow at the kitchen tap before quoting, and ask what the block's supply arrangement is.
What the job looks like
- Survey.Gas meter and pipe size, flue position against TGD J, mains flow, and what the management company needs to agree.
- Old combi out, new one in.A straight swap in the same spot is usually a day's work.
- Flue and plume.Through the existing hole if the distances work; a plume kit or a new position if they don't.
- Flush, filter, commission.A chemical flush, a magnetic filter, inhibitor and the RGI's commissioning.
- Certificate.A CERT 2 completion certificate for a boiler replacement, the original white copy, straight after the job (RGI). Keep it: the management company or a buyer may ask for it.
Landlords with apartments
If the apartment is let, the gas installation must be kept in safe working order under the rented housing standards, and the way to show it is an RGI's Annex E inspection with its certificate. Our sister site sets out what the law asks of landlords.
Questions people ask
Can you put a combi boiler in an apartment?
Yes, if the apartment has a gas supply and the flue can end outside within the Building Regulations distances. A like-for-like swap of an existing combi through the same flue hole is the simplest job.
How much is a combi boiler for an apartment?
Priced like any combi swap: a median €2,600 across 12 installers' published prices. A moved flue, a plume kit or awkward access add to it.
Do I need the management company's permission?
For a new flue hole, a moved terminal or scaffolding, usually yes, because the outside wall is common property. For a like-for-like swap through the existing flue, usually not. Ask before the installer quotes.
How far must the flue be from a window?
TGD J gives 300 mm directly below an opening window, vent or air brick for a room-sealed fanned-draught terminal, 300 mm horizontally from a door, window or vent, and 1,200 mm from a terminal facing another terminal.
My apartment has no gas. What are the options?
An electric combi or an electric boiler with a cylinder. See electric combi boilers. Bringing gas to a block is rarely practical.
What size combi does an apartment need?
Small on heating, but sized for hot water. A 25 kW combi gives about 10.5 litres a minute at a 35 °C rise on Vaillant's figures, enough for one shower. One installer's guide puts a small house or flat at 9–18 kW.
Sources (2)
Prices and facts on this page were checked against these published pages. We are not connected to these businesses.
- gasboiler.ie: gasboiler.ie
- Vaillant technical sheet: professional.vaillant.co.uk
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