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.
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.