What is an air-to-air system?
An air-to-air system is a heat pump that moves heat between the air inside your home and the air outside. It has an outdoor unit (the compressor) connected by thin pipes to one or more indoor units that deliver conditioned air into the room.
The key thing to understand: most modern systems are reverse-cycle. In summer they pull heat out of your home to cool it; in winter they run in reverse, drawing warmth from the outside air — even when it's cold — to heat your home efficiently.
The two families
Cooling-only
Cheaper upfront. Only cools. Best where you never need heating.
Reverse-cycle (heat pump)
Cools and heats from one unit. Far more efficient than electric heaters. The right choice for most UK homes.
Cooling vs heating vs both
Your first real decision is what you need the system to do across the year. This shapes everything that follows.
| Your need | Best choice | What to check |
|---|---|---|
| Cool summers, mild winters | Cooling-only or reverse-cycle | SEER rating |
| Cold winters, warm summers | Reverse-cycle | SCOP + low-temp output |
| Year-round comfort | Reverse-cycle (both) | Both SCOP & SEER |
| Replace old gas / electric heating | Reverse-cycle | SCOP, running cost vs gas |
Understanding the efficiency ratings
- SEER (Seasonal Energy Efficiency Ratio) — how efficiently it cools across a season. Higher is better.
- SCOP (Seasonal Coefficient of Performance) — how efficiently it heats. A SCOP of 4 means 4 units of heat for every 1 unit of electricity.
Single-split vs multi-split
Once you know what the system should do, decide how many rooms it serves. This is the choice between single-split and multi-split.
Single-split
One outdoor unit → one indoor unit. Simple, efficient, cheapest. Ideal for a single room: lounge, bedroom, home office.
Multi-split
One outdoor unit → several indoor units. Fewer outdoor boxes on your wall. Each room controlled independently. Best for whole-home comfort.
How to decide — step by step
- 1 room? Single-split. Done.
- 2–3 rooms close together? Multi-split saves wall space and outdoor clutter.
- Rooms far apart or on different floors? Sometimes two single-splits are cheaper and simpler than one long multi-split run.
- Adding rooms over time? Choose a multi-split outdoor unit sized with spare capacity now.
Sizing your system
Size is where most people go wrong. Too small and it runs flat-out and never quite copes. Too big and it short-cycles, wastes energy, and feels clammy. Use the calculator below for a quick estimate.
Quick room calculator
Estimate the cooling / heating capacity (kW) your room needs.
Unit types & placement
Indoor units come in several shapes. The right one depends on your room, your ceiling and how visible you want it to be.
High-wall
Mounted high on a wall. Most common, most affordable, quick to install. A great all-rounder.
Floor console
Sits at floor level like a radiator. Excellent for heating; good where wall space is limited.
Ceiling cassette
Recessed into the ceiling, blows in four directions. Discreet, even airflow. Needs a ceiling void.
Ducted
Hidden in the roof, air through vents. Near-invisible, whole-home feel. Highest cost & install effort.
Placement basics
- Mount the indoor unit where air can circulate freely — not blocked by furniture or curtains.
- Avoid blowing air directly onto where you sit or sleep.
- Keep the outdoor unit ventilated, shaded if possible, and away from bedroom windows (noise).
- Shorter pipe runs between indoor and outdoor units mean better efficiency.
Before you buy — checklist
Tick these off before you commit. Click each item once you're happy with it.
Ready for the right system?
You've done the homework. Let ArcticNord's F-Gas registered engineers turn it into a precise recommendation with a free survey and a fixed, written quote.