Both are German-engineered Viessmann systems — but one is an all-electric heat pump and the other a condensing gas boiler. Here's how the Vitocal and Vitodens 100-W compare on running cost, cooling, flow temperature and best-fit — and how AHHAC chooses between them.
Viessmann Vitocal vs Vitodens is a choice between an electric heat pump and a gas condensing boiler. Choose the Vitocal if you're going all-electric, have solar, want low 35–55 °C underfloor temperatures or summer cooling. Choose the Vitodens 100-W if you already have mains gas, existing high-temperature radiators and want the lower upfront cost — it reaches up to 98% efficiency. AHHAC installs and services both Viessmann systems.
Reviewed by the AHHAC Technical Team — licensed plumbers & hydronic engineers, NSW Lic 262528C.How we write & review
ImmergasSimeThermaSkirt™| Vitocal (heat pump) | Vitodens (gas boiler) | |
|---|---|---|
| Technology | Hydronic heat pump (electric) | Condensing gas boiler |
| Energy source | Electricity (+ solar) | Natural gas / LPG |
| Efficiency | COP 3–4.5 (300–450%) | Up to ~98% net |
| Running cost | Lowest — near zero on solar | Tracks gas price |
| Cooling | Yes — reversible models | No — heating only |
| On-site emissions | Zero (near-zero with solar) | Low-NOx combustion |
| Best flow temp | Low 35–55 °C (underfloor-ideal) | High to ~75–80 °C (radiator-ideal) |
| Upfront cost | Higher | Lower |
| Best for | New builds, all-electric, cooling too | Gas homes, high-temp radiator retrofits |
Indicative technology figures; AHHAC sizes and quotes to your heat-loss calculation and fuel access.
…you're building new or renovating with underfloor, you want the lowest running cost (especially with solar), you want one system that also cools in summer, or you're going all-electric and gas-free. It thrives at the low 35–55 °C flow temperatures underfloor and modern radiators use.
→ Viessmann Vitocal heat pump…you already have mains gas, want the lowest upfront cost, need high flow temperatures for existing high-output radiators, or want the fastest warm-up on demand. The Vitodens 100-W is a compact, quiet, ~98%-efficient condensing boiler ideal for radiator retrofits.
→ Viessmann Vitodens 100-W boilerBecause we carry both, the recommendation follows your home — not our stock. We start with a heat-loss calculation, then weigh four things: fuel access (no gas, or going all-electric → Vitocal), emitter type (low-temp underfloor → Vitocal; existing high-temp radiators → Vitodens), whether you want summer cooling (yes → only the reversible Vitocal can), and upfront budget (tighter → Vitodens). Many homes land on a heat pump for a new build and a condensing boiler for a gas-connected radiator retrofit.
For the underlying economics that drive this choice, read our full guide on electric boiler vs heat pump hydronic heating, or compare the wider market on our Maxa vs Viessmann vs Immergas page. You can also explore all our hydronic heat pumps and hydronic boilers.
Plenty of homeowners don't need to pick one Viessmann technology forever. A staged approach — keeping gas where it still makes sense and electrifying where the savings come easiest — is often the most practical path, especially when an old boiler and an old hot water tank are both near the end of their lives.
A useful nuance first: the Vitocal 161-A in our range is a domestic hot water heat pump, available in 200 L and 270 L, rather than a space-heating unit. That makes it a natural partner for a gas heating boiler as much as a rival to one.
Where this doesn't apply: for new builds — particularly in Victoria, which no longer allows new gas connections for most new homes, and the ACT, which has stopped new gas network connections — we go straight to all-electric. A hydronic heat pump such as the Maxa i-290 handles space heating and cooling, with hot water from the same unit or a Vitocal.
For the cost side of each step, see our guide to hydronic heating costs in Australia, and if you're keeping radiators, our central hydronic heating flushing page explains why clean water matters for whichever heat source comes next.
Written from on-site experience by the AHHAC Technical Team.
AHHAC's in-house design and service team — licensed plumbers and hydronic engineers (Lic 262528C) who have designed and installed 2,400+ hydronic heating, cooling and hot water systems across Australia since 1998.
We only specify equipment after a heat-loss and system-compatibility check, then supply, install and commission it with our own licensed plumbers to AS/NZS 3500 (plumbing) and AS/NZS 5601 (gas), register the manufacturer warranty and service it for the life of the system.