Indirect Oil Fired Air Heaters

An oil heater with flue gas exhaust is an indirect unit: the oil burns in a sealed chamber with a heat exchanger, and the flue gases escape through the flue outlet and chimney to the outside. A fan pushes air across the outer surface of the hot exchanger, so the air returning to the hall is heated but separated from the combustion products. Master BV series models come in various power ranges — from workshop units to large hall heaters; the exact power and oil consumption are given on the product page.

A model with flue gas exhaust (indirect) vents the combustion products outside through a chimney, so you can heat in enclosed, ventilated halls and the air stays dry and clean. The version without exhaust (direct) gives all the heat to the room, but together with flue gases and water vapour, adding about 1.2 l of water per 1 l of fuel. The efficiency of the indirect type is about 80–90%, of the direct type almost 100%.

Power is matched to volume and insulation — for a well-insulated building about 2.5–3 m high, a rough figure of 0.1 kW per 1 m² is used. For a workshop or smaller hall, 10–20 kW is usually enough, for a medium production building 30 kW, and for large halls and construction sites 40–50 kW. In poorly insulated buildings the demand can rise up to twofold.

A 20 kW heater will heat a well-insulated room up to about 200 m² (volume about 500 m³), and a 30 kW model up to about 300 m² (about 750 m³) at a height of about 2.5–3 m. These are figures for insulated buildings — in a poorly insulated hall the real range drops by as much as half, which is why power is chosen with a 10–20% reserve.

Oil consumption rises in proportion to power and is roughly about 0.1 l per hour for every 1 kW. A 10 kW model burns about 1.0 l/h, a 20 kW one about 2.0 l/h, a 30 kW one about 2.9 l/h, and a 50 kW one about 4.7 l/h. With a tank of several dozen litres this gives from a few to a dozen hours of operation per fill.

An indirect heater is designed to work in enclosed, ventilated rooms, because it vents the flue gases outside through a chimney and only clean air enters the hall. The condition is a correctly connected chimney with a diameter of 120–150 mm and a vertical section, plus a supply of fresh air for combustion. It is also worth using a carbon monoxide detector and servicing the burner regularly.

The chimney pipe is connected to the flue outlet on the heater casing and led outside — vertically above the roof or through a wall using elbows and a roof penetration. The pipe diameter (usually 120–150 mm) must match the outlet of the given model. The vertical section is crucial, as it creates the draught; long horizontal runs weaken the draught and encourage condensation.

Oil heaters with flue gas exhaust are most often powered by diesel or heating oil, and some models also allow kerosene. Heating oil can be cheaper, but its use depends on regulations and the intended purpose of the building. Do not use petrol or solvents. Always check the manual to see which fuel a given model allows, and use clean fuel free of contaminants.

The price depends primarily on power and equipment. Smaller indirect models for workshops start at roughly a few thousand zloty, medium-power units fall in the range of several to a dozen or so thousand, and large multi-duct heaters of the Master BV 400 or BV 471 class cost from a few to a dozen or so thousand zloty. Current prices are given on the product pages.

The best model is the one matched to the volume and way of working. Master Heaters (the BV 110–471 series) is the widest range, with mobile and multi-duct 4-way models, covering a wide power range. Heylo works well in industrial applications, and Sovelor in workshops and halls. For most workshops and halls the starting point is the smaller models of the Master BV series; for large buildings you choose the BV 400 or BV 471. The exact power of each model is given on the product page.