Heating Replacement: Gas/Oil Boiler to Pellet Boiler

Replacing a fossil-fired heating system with a modern pellet boiler. Substitutes fossil fuel with carbon-neutral wood.

How does switching from gas or oil to a pellet boiler work?

A pellet boiler burns standardised compressed wood pellets certified to ENplus-A1, which are transported automatically from a store into the combustion chamber by screw conveyor or suction system. Modern systems achieve efficiencies of 90 to 95 %, condensing pellet boilers up to 97 %. Like a fossil-fuel boiler, the pellet boiler delivers flow temperatures of 70 °C and above and can be integrated into the existing system without changes to radiators or distribution. Because wood binds as much CO2 during growth as is released during combustion, the fuel is considered almost climate-neutral; only the upstream chain (production, transport) accounts for around 0.022 kg CO2/kWh. Requirements are a pellet storage room, a fabric silo or an underground tank, plus a chimney suitable for solid fuels.

Which buildings are suitable for a pellet boiler?

A pellet boiler is the right choice above all when the building requires high flow temperatures and a heat pump is not economically viable – in other words, in unrenovated existing buildings with radiators. Typical buildings are detached houses and apartment buildings, rural locations, small commercial premises, as well as parish and municipal buildings. A storage room is a prerequisite: around 0.9 m³ of storage volume is needed per 1,000 kWh of annual demand. The access road must be suitable for the pellet delivery lorry, usually with a hose length of up to 30 m. Excluded are very dense residential areas with particulate matter issues or protected zones, and buildings with no space for storage.

What does switching to pellets actually deliver?

Final energy demand falls by 10 to 25 % because the new boiler operates far more efficiently than an old one. The real effect is on emissions: around 95 % less CO2. An apartment building with a heat demand of 87,000 kWh saves about 17,000 kWh of final energy and 27.6 t of CO2 per year. The investment is 15,000 to 25,000 € for a detached house and 35,000 to 80,000 € for an apartment building, in each case including storage and screw conveyor. Over a 20-year service life, payback is 10 to 18 years – subsidies for boiler replacement shorten this noticeably.

Energy carrier

Erdgas, Heizöl → Pellet

Savings potential

10-25 % Endenergie, ~95 % CO2

Worked example

An apartment building with 800 m² of usable floor area and a space heating demand of 90 kWh/(m²·a) requires 72,000 kWh of space heating plus 15,000 kWh for hot water, 87,000 kWh/a in total. The old oil boiler operates at an efficiency of 0.78 and consumes around 111,500 kWh of heating oil per year. The new pellet boiler achieves 0.92 and needs only 94,600 kWh in the form of pellets. The final energy saving is calculated as 87,000 × (1/0.78 − 1/0.92) = 87,000 × (1.282 − 1.087) = 87,000 × 0.195 = 16,965 kWh/a. For the CO2 balance, 111,500 kWh × 0.266 kg/kWh for heating oil is compared with 94,600 kWh × 0.022 kg/kWh for pellets: 29,659 kg − 2,081 kg = 27,578 kg CO2/a. The building therefore saves around 17,000 kWh of final energy and about 27.6 t of CO2 per year.

Investment & payback

EFH: 15.000-25.000 €; MFH: 35.000-80.000 € inkl. Lager und Förderschnecke · Service life: 20 a · Payback: 10-18 (Förderung Heizungstausch beachten) a

Applicability

Requirements

Exclusion criteria

Typical buildings

Frequently asked questions

How much does a pellet heating system cost for an apartment building?

A pellet heating system for an apartment building costs 35,000 to 80,000 € including boiler, pellet store and screw conveyor. For a detached house, costs are 15,000 to 25,000 €. The range depends on boiler output, storage solution (storage room, fabric silo or underground tank) and the effort required for chimney refurbishment. Over a 20-year service life, the system pays back in 10 to 18 years, correspondingly faster with subsidies.

How much space does a pellet store need?

A pellet store requires around 0.9 m³ of storage volume per 1,000 kWh of annual heat demand. For a detached house with 20,000 kWh, that is about 18 m³ of storage, equivalent to a cellar room of 6 to 8 m² floor area. Where space is tight, fabric silos or underground tanks are an alternative. The storage room should be located on an external wall so that the delivery lorry can fill it with pellets via blow-in couplings.

Is a pellet boiler worthwhile compared with a heat pump?

A pellet boiler is worthwhile above all in buildings that require high flow temperatures and will not be refurbished in the short term. Like a fossil-fuel boiler, it delivers 70 °C and above and requires no changes to the radiators. The heat pump is more efficient and lower-maintenance at low flow temperatures, but loses considerable efficiency in uninsulated old buildings. In terms of CO2 balance, both are at a similarly low level.

Which standards and quality requirements apply to pellet heating in Austria?

In Austria, ÖNORM EN 303-5 governs the requirements for solid-fuel boilers and ÖNORM M 7136 the storage of pellets. The fuel itself should meet quality class ENplus-A1, which specifies ash content, moisture and calorific value. The method for calculating savings is described in the Austrian Energy Efficiency Guidelines Regulation 2016. Before installation, the chimney sweep must confirm that the chimney is suitable.

How much CO2 does pellet heating save compared with oil?

Pellet heating saves around 95 % of CO2 emissions compared with an oil boiler. Heating oil causes 0.266 kg CO2/kWh, pellets only about 0.022 kg CO2/kWh from the upstream chain, because combustion itself is considered climate-neutral. An apartment building with a heat demand of 87,000 kWh reduces its emissions from around 29.7 t to about 2.1 t of CO2 per year. With natural gas at 0.201 kg CO2/kWh, the saving is somewhat smaller.

Related measures

Standards & sources

Metering points in the EDM Toolbox

Empfohlene EDM-Messpunkte: (1) Wärmemengenzähler, (2) Pelletverbrauch (Schneckenzähler oder Lagerstand), (3) Vorlauf-/Rücklauftemperatur, (4) Außentemperatur. Pelletverbrauchsmessung optional via Wägezelle unter Tagesbehälter.

All measures