Keep the clearance the boiler manufacturer sets around the flue terminal, and the clearance the air conditioning manufacturer sets for the outdoor unit. Flue gas and a coil are a bad mix: the coil corrodes and the flue must stay clear for the boiler to be safe. This page does not invent a one-metre rule or any other homemade distance. If both manuals cannot be met, the outdoor unit moves. Moving the flue is gas work for a qualified person, not part of the F-gas install and not a job described here.
The boiler plate and the condenser manual
The plate on the boiler or its installation book states how close another object may be to the terminal. The air conditioning manual states how close the condenser may be to a flue, a wall, or a heat source. Use the stricter result that satisfies both. A forum metre, or a gap that looks like enough, is not a third manual. Terminals on a side wall, under a carport, or in a basement area are already in a crowded drawing. Adding a condenser because the wall is free is how the flue clearance disappears. If they clash, move the condenser, not the guess.
Who may touch the flue, and who commissions the split
The split is commissioned by an F-gas certified company. The boiler flue, if it has to change, is a separate competent person and a separate price. One van that offers both should still show you both qualifications. The condenser's position remains a Planning Portal question in England. A spot that respects the flue and breaches a boundary condition is still the wrong spot.
Frequently asked questions
How many metres should the outdoor unit be from the flue?
As many as the two manuals require, and no invented round number. If you have not read them, the installer must, and the price should say the clearances used. Boiler manufacturer clearance around the flue, and air conditioning manufacturer clearance for the outdoor unit. No invented metre rule.
Can I fit a short flue extension to make room?
Only a qualified person can alter a boiler flue, against that boiler's instructions. It is not part of a DIY air conditioning fit, and this page does not describe it. Do not extend, cap or redirect a flue as part of a weekend air conditioning plan.
What if the only wall is the flue wall?
Then a split may not fit until a lawful flue clearance and a lawful condenser clearance both exist. Look at another elevation or another design rather than closing the gap.
What happens to the coil if flue gas is drawn through it?
Flue products drawn through the coil attack the fins and the cabinet. The heat pump then runs hot, noisy and short-lived. That is why the two clearances both have to be met.
Can the condenser fan disturb the boiler?
The boiler's own air supply and the plume from the terminal can also be disturbed by a fan blowing across the terminal. That is a safety question for the boiler, to be judged by someone qualified on gas appliances.
Does a heat pump note override the boiler manual?
No. Energy Saving Trust's heat pump notes do not override a boiler manual. If both manuals cannot be met, the outdoor unit moves. Moving the flue is not part of the F-gas install and is not a job described here.
Core buying guides
Start with these high-intent guides, then dig into the rest of the library.
Related guides
Sources and further reading
How this guide was prepared
This guide was written by the Local AC Installers Editorial Team. We compare official guidance, legislation and established consumer information, separate general information from project-specific advice, and show publication dates and sources. We do not accept installer accreditation claims at face value.