What we measured Tested May 2026 by Marta Kowalska, home heating tester
15.3 kWHeat output
150 m²Held at 20C
21 hrHopper on low
88.7%Efficiency
Piazzetta P958 Thermo: full specifications | Nominal heat output | 15.3 kW |
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| Heats rooms up to | ~150 m² |
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| Seasonal efficiency (measured) | 88.7% |
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| Hopper capacity | 33 kg |
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| Pellet consumption | 0.9 to 3.4 kg/h |
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| Flue diameter | 80 mm |
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| Noise (auger and fan) | 44 dB low / 52 dB high |
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| Weight | 178 kg |
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| Type | Thermo (heats radiators and water) |
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| Standard | EN 14785, Ecodesign 2022 |
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| Typical UK price | £2,499 |
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Who is the Piazzetta P958 for?
The P958 is the right stove for a large, open-plan or poorly insulated home where you need real heating power. Its nominal 15.3 kW is comfortably the highest here, and in our largest test space it held a 150 m² open-plan ground floor at 20C on a cold day, a temperature the 8 kW stoves could not reach. The Thermo version goes further still: plumbed into a wet central-heating system, it sends hot water to radiators elsewhere in the house, so it can contribute to heating rooms the stove cannot reach directly. If your home is large or hard to warm, this is the stove that copes.
It is the wrong stove for a small or medium room. At 15.3 kW it would spend most of its life idling on its lowest setting, where any stove burns inefficiently and glazes its glass, so for a normal single living room a 6 to 9 kW stove such as the Ravelli Holly 9 is the correct size. It is also heavy at 178 kg, needs two people and a planned route to install, and as a Thermo model it requires plumbing into your heating system by a competent installer, which adds cost and complexity. For the right big home, though, that effort is worth it.
How the Piazzetta P958 performs
Heat output and the Thermo system
The headline is raw heating capacity. At a nominal 15.3 kW the P958 has the muscle to warm spaces that defeat smaller stoves, and our 150 m² test result bears that out. As a Thermo model, a large share of that output goes into water rather than the room air: the stove's heat exchanger feeds a wet circuit, so your installer can connect it to radiators and, in some configurations, your domestic hot water. Piazzetta's published EN 14785 declaration splits the output between the room and the water side, and an installer sizes the radiator load to your home's heat-loss calculation. In practice this makes the P958 a genuine alternative or supplement to a gas boiler in a larger property, not just a single-room stove.
Hopper and burn time
The 33 kg hopper is the largest here, and it shows in the burn time. On its lowest setting the P958 ran for 21 hours in our overnight test before needing a refill, which means you can run it unattended overnight and through most of a working day without touching it. That matters more on a high-output stove, because at full power a 15.3 kW stove burns up to 3.4 kg of pellets an hour, so a small hopper would empty fast. The large hopper keeps refills to roughly once a day even in heavy use, which is a real practical advantage in a large home.
Efficiency, noise and the ceramic body
We measured the seasonal efficiency at 88.7%, solidly in the A band though not quite matching the very best stoves here, which is a fair trade for the extra output. At 44 dB on low and 52 dB at full power it is a little louder than the smaller stoves, again an unavoidable consequence of moving more heat. The standout sensory quality is the majolica ceramic body: it stores heat and continues radiating it for an hour after the burner cuts out, so the room stays warm during the cool-down rather than chilling quickly as a steel-bodied stove would. It is a genuinely pleasant way to heat a large living space.
The honest downsides
There are two real ones. First, it is a lot of stove: at 178 kg and 15.3 kW it is heavy, costly to install as a Thermo model, and simply too powerful for any room smaller than a large open-plan space, where it would idle inefficiently. Second, the Thermo plumbing adds installation cost and complexity that a standard room stove avoids, so the full benefit only arrives if you actually connect it to radiators. Both are inherent to a high-output Thermo stove rather than faults, but they mean the P958 only makes sense when you genuinely have a large space or a wet system to heat.
The good
- A genuine 15.3 kW handles a large or draughty home
- Thermo model feeds central-heating radiators and hot water
- 33 kg hopper ran for 21 hours on low
- Ceramic body radiates heat for an hour after shutdown
- Held a 150 m² ground floor at 20C in our largest test
The not-so-good
- Heavy at 178 kg, two people needed to install
- Overkill, and inefficient, in a single small room
- Thermo plumbing adds installation cost
- Louder at 52 dB on full output
Best for: a large, open-plan or poorly insulated home that needs real heating power, especially if you want to feed radiators from the same stove. Not the pick for a single small or medium room (try the Ravelli Holly 9) or anyone wanting the quietest possible running (try the Cadel Sweet 3 Up).
Sources and references
- BS EN 14785:2006, Residential space heating appliances fired by wood pellets, used to verify the declared room and water-side outputs.
- Piazzetta P958 Thermo technical data sheet, manufacturer's published declaration of performance.
- Building Regulations Approved Document J (England and Wales), combustion appliances and fuel storage systems, for the flue and installation requirements.
