OFTEC Solid Fuel cheat sheet

Complete combustion of kerosene requires roughly 12.5 kg of air per kg of fuel; CO2 in flue gas near 12% indicates good excess-air control.

Smoke number is read against the pump's reference scale: 0-1 is clean, 2 acceptable, 3+ indicates poor atomisation or wrong air setting.

Nozzle flow rate varies with pressure by the square-root law: doubling pressure multiplies flow by about 1.41.

Standard nozzle rating pressure is 100 psi (7 bar); flow markings (e.g. 0.60) are US gallons per hour at that pressure.

Flue gas temperature should typically exceed boiler return temperature by 20-40 C for a condensing boiler to be in condensing mode.

Oil line vacuum should not exceed about 0.4 bar (roughly 12 in Hg); higher vacuum signals a blocked filter, kinked line or faulty foot valve.

Fire-valve and photocell (cad cell) resistance: a clean flame gives low resistance (typically under 1-2 kOhm); high resistance means weak flame or dirty cell.

Tigerloop/one-pipe lift systems are used where the tank is below the burner; two-pipe gravity systems are used where the tank is above the burner.

Solid fuel appliances require a permanent, unobstructed combustion air supply; a ventilator sized to the appliance's rated input is mandatory.

Chimney draught is driven by temperature difference: hotter flue gases give more draught, so a cold flue is a common cause of poor performance.

A flue serving a solid fuel appliance should terminate above the roof line and clear adjacent openings in accordance with building regulations.

Wood fuel moisture content should be around 20% or lower; wet wood causes tar/creosote deposition and reduced net efficiency.

Anthracite and other smokeless fuels are required in smoke control areas; bituminous coal is generally prohibited there.

A gravity-fed solid fuel system must include an open vent and a cold feed; a closed, unvented arrangement on a solid fuel boiler is unsafe.

Regular servicing includes sweeping the flue, checking baffles, seals, door gaskets and the draught stabiliser.

Over-firing (excessive primary air) shortens appliance life; under-firing causes incomplete combustion and soot.

Final circuits in domestic premises are protected by 30 mA RCDs; a 6 A MCB typically protects a 1.0-1.5 mm2 lighting/control circuit.

Cable current-carrying capacity must be derated for grouping, ambient temperature and thermal insulation (BS 7671 factors).

A boiler's switched live (SL) terminal is fed from the room/programmer controls; permanent live (PL) provides power for pump overrun and frost protection.

Earth loop impedance must be low enough for the protective device to disconnect within the required time at the stated fault current.

SELV controls (e.g. 24 V or 0-10 V) must be kept separate from mains wiring; separation barriers and correct cable colours apply.

Functional switching and isolation: each appliance needs a means of isolation, and a double-pole switch is used for maintenance isolation.

Motorised valves are typically 3-port (mid-position) or 2-port (zone); a 3-port valve has a mid-position that supplies both heating and hot water.

Bonding of metallic pipework is required where it is an extraneous conductive part; supplementary bonding may be needed in bathrooms.

Heat pump COP = heat output (kW) / electrical input (kW); seasonal performance factor (SPF) is the same ratio over a whole season.

Carnot efficiency sets the theoretical maximum COP: COP_max = T_hot / (T_hot - T_cold) with temperatures in kelvin.

Lower flow temperatures (e.g. 35-45 C) improve heat pump COP; underfloor heating suits this better than high-temperature radiators.

A heat pump's heat output must be sized to the building's heat loss at design external temperature, not to the existing boiler rating.

Ground-source collectors need adequate ground area; boreholes are used where land is limited, and loop length depends on ground thermal conductivity.

Solar thermal yield depends on collector area, orientation and tilt; a south-facing tilt of about 30-45 degrees in the UK is typical.

Biomass boilers require fuel storage, delivery access and flue arrangements; efficiency is rated on a gross or net calorific value basis.

Thermal stores decouple heat generation from demand and are often required with heat pumps and biomass to buffer output.