Indicative figures; AHHAC sizes and quotes to your heat-loss calculation.
How each one works
Both emitters do the same job — turn warm water from a heat pump or boiler into comfortable room heat — but they do it differently. Underfloor embeds PEX-A pipework in the floor (in the concrete slab for new builds, or in a thin screed over an existing subfloor) and turns the whole floor into a large, low-temperature radiator. Radiators are wall-mounted steel or aluminium panels that heat quickly and can be turned up or down room by room. Underfloor is a distributed, invisible, thermal-mass system; radiators are compact, responsive point sources. That single difference — mass vs responsiveness — drives almost every other trade-off below.
Warm-up speed and comfort
Radiators win decisively on speed: they warm a room from cold in 15–25 minutes, so they're perfect for spaces you use intermittently — bedrooms, studies, guest rooms — where you want heat now and off again when you leave. Underfloor is slow by design, taking 2–8 hours to bring a slab up to temperature; it's built to run as a steady, low-temperature background warmth rather than to blast on and off. On pure comfort, underfloor edges it: the warmth is perfectly even from floor to ceiling, there are no hot spots, and there's nothing on the wall. Radiators are also even and quiet, but they're a visible presence in the room (which some owners turn into a design feature with vertical or designer panels).
Running cost and efficiency
Underfloor is marginally cheaper to run because it operates at a very low flow temperature (35–45 °C), which is exactly the band where a heat pump is most efficient. Radiators run a little hotter (45–55 °C on modern oversized panels), so the heat pump works slightly harder — but the gap is small, and both are far cheaper to run than ducted electric or a resistive system. The heat source matters far more than the emitter here: a heat pump on either emitter will beat a gas or electric boiler on running cost. We cover the full picture in our hydronic heating cost guide.
Install cost and retrofit
This is where radiators pull ahead for existing homes. A full radiator system typically costs $12,000–$30,000 and installs in one to three days using a manifold-and-home-run pipe layout with no joins in walls and no floor works. Underfloor costs more — $22,000–$45,000 for an in-screed retrofit, $30,000–$55,000 for in-slab in a new build — and in a finished home the in-screed build-up raises the floor height. The rule of thumb: for a new build or a renovation with new floors, underfloor is a small incremental cost and the best result; for a retrofit into a finished home, radiators are usually the smarter, less disruptive spend.
Zoning, aesthetics and space
Both give excellent room-by-room control — underfloor via per-room thermostatic zones at the manifold, radiators via a thermostatic valve (TRV) on every panel. On aesthetics and space, underfloor is invisible and frees every wall, which architects love; radiators occupy a section of wall but can be specified as slim panels, vertical design pieces, column radiators for heritage rooms, or dual-fuel towel rails in bathrooms. Neither compromises air quality — unlike ducted, there's no recirculated dust or dry air with either.
Can they cool?
Only underfloor can. On a reversible heat pump, the same underfloor loops run chilled water in summer for silent, draught-free floor cooling — so one system covers both seasons. Radiators are heating-only. If year-round comfort from a single hydronic system matters to you, that tips the scales toward underfloor (or toward adding fan coils). See our guide to radiant floor cooling for how it works.
How AHHAC decides — and why "both" is often the answer
Because we install both, the recommendation follows your home, not our stock. We start with a heat-loss calculation, then weigh the build (new vs retrofit), how you use each room (constant vs intermittent), budget, and whether you want summer cooling. Very often the best answer is a blend: in-slab underfloor through the open-plan living areas for even, invisible, coolable comfort, and fast-response radiators in bedrooms, bathrooms and additions. Both run from the same heat source, so a hybrid system is straightforward. For the wider technology choice, see our guide to ducted vs hydronic heating, and avoid the classic sizing pitfalls with our guide to mistakes to avoid.
