Brivis installer, Melbourne’s south-east.

The Wombat is the straight swap. It shares its footprint with the older Brivis and Braemar units, so the existing ducts, controller wiring and return-air grille all stay where they are and the job is usually done in a day. It's a 3-star heater, which is the right call for a house that's being sold, rented out, or heated a few weeks a year. If you're staying and running it all winter, a Starpro burns less gas doing the same work, and we'll show you both numbers.

Same in-cupboard footprint as the Wombat, with a better fan and a longer service life behind it. What usually decides it is noise: when the heater cupboard backs onto a bedroom or the hallway you walk down at 6am, that's the difference you actually notice. Fit it and forget about it for 15 years.

Starpro 4/5-star is where the gas bill starts to move. Same in-cupboard footprint as the Wombat so the retrofit stays clean, and enough of an efficiency gain that a family running the heater every day through a Melbourne winter feels it on the bill. The 6-star adds a modulating burner on top of that, which is worth having in some houses and not in others, and we'll tell you which yours is.

The modulating burner is what you're buying here. Instead of firing flat out and shutting off, it varies its output to match what the rooms are asking for, so there's less temperature swing and less gas burnt getting there. It earns its money in a house that heats a lot of hours, and it's the most efficient gas ducted heater Brivis builds.

The outdoor-cabinet build, weatherproofed, with the quieter fan and longer service life of the internal Compact Classic. Common on the older Berwick, Endeavour Hills and Cranbourne weatherboards where the heater has always sat on a slab down the side of the house, and where the existing pad and gas line come straight across.

Starpro External in 4-star or 5-star, for the house with the heater outdoors that runs it hard enough to care what the gas costs. Same weatherproof cabinet footprint as the Buffalo External, so the existing pad and gas line get reused and nothing new gets poured.

The modulating burner, in the weatherproof cabinet. Output varies to match what the house is asking for rather than cycling hard on and off, which is the difference you feel in a home that heats a lot of hours. The most efficient outdoor-cabinet heater Brivis makes.

The Contour is the Classic profile, the taller cabinet. It's what goes on when the roof pitch carries it and nobody minds how it reads from the footpath, which covers most houses. Cools a whole home for a fraction of what refrigerated ducted costs to run, as long as the day is dry, and most Melbourne days are.

Same cooling as the Contour, in a flatter cabinet. It goes on when the roofline is the thing that matters: a character street in Berwick, an Officer estate with covenants, or a low-pitch roof where the taller cabinet sits awkwardly. You're buying the silhouette rather than the cooling, and that's a fair reason to buy it.