Discussion of Unit Heater Types

There are a wide range of Unit Heater Types on the market today. While many are versatile enough to be used in a wide variety of ways, others are designed for niche applications.

Whereas radiant heaters, operating at a very high surface temperature are suited to ‘spot-heating’ applications (of say, a particular workbench) they are not generally a good selection for space heating. In contrast to a radiant heater, Unit Heaters use a fan to produce a high-volume flow of air which distributes the heat generated evenly and efficiently around the environment in which it is installed. Any heater will have limitations as to how widely the heat can be distributed and for larger spaces multiple Unit Heaters may be required.

Although the heat is distributed in almost all cases by an integrated fan, the heat may be generated in a variety of ways. Selection is often driven by the most readily available and economical fuel for the user.

  • Unit Heater Types – Circulating Hot Water Systems

    Unit Heater Types - Hot Water Fed, Wall Mounted

    Wall-mounted Unit heater with hot water feed

    Unit Heater Types - Hot Water Fed, Ceiling Mounted

    Ceiling mounted Unit Heater with hot water feed

    Hot water is generated by a central boiler and is then circulated to one or more low pressure hot water (LPHW) unit heaters. These LPHW unit heaters are used in many applications, such as for heating shop entrances, warehouses, industrial premises, workshops and sports halls. The fans have a low sound level and offer reliable operation. Many have optional ancillary control equipment including electronic thermostat that starts/stops the fan and opens/shuts off the water flow. If heating is not required the fan may continue to run to provide ventilation if required. Multiple unit heaters can be controlled with a single external room sensor and set point adjuster. Some LPHW unit heaters are equipped with drip pans and drains and they can be used for cooling as well as heating.

  • Unit Heater Types – Steam Fed Heaters

    Unit Heater Types - Steam Fed Heater

    Steam Fed Unit Heater

    Some boilers produce hot water but others produce steam. Steam unit heaters are in many ways similar to LPHW unit heaters, however although they have a coil and a fan to blow the air through the coil, the coil itself is of a far heavier construction. The operating principle of a steam unit heater is slightly different to a LPHW heater in that the coil is engineered to make the fluid not only transfer its heat to the air but also to change state. The steam condensing in the coil liberates more heat than just cooling the steam but maintaining its steam state.  The output of steam unit heaters is greater with larger pressure in the steam pipe and the Thermolier steam unit heaters that we supply are ideal for connection to piped steam supplies with up to 10 bar.


  • Unit Heater Types – Standard Electric Heaters

    Unit Heater Types - Standard Electric Heater

    Wall mounted standard electric Unit Heaters

    These basic units range from 3kw upwards and are targeted at the medium sized industrial premises. Models are available for both single phase ands three phase applications. The hot air ‘throw ranges from 9 – 16 metres. To comply with Ecodesign Regulation (EU) 2015/1188 these units must be installed with an external thermostat (such as TAP16R accessory). TAP16R has adaptive start, week program and open window detection.


  • Unit Heater Types – Electric Heaters for Specialised Applications

    Unit Heater Types - Specialised Electric Heater

    Wall mounted specialised electric Unit Heaters.

    Selection will depend on the environment within which the heater is to be applied. The model shown is available in 4 versions. Elektra C is intended for corrosive and damp environments, for example, car-wash halls and sewage works with an outer casing of acid-proof sheet steel, rated IP65.  Elektra F has a low element temperature and is approved for use in combustible areas, for example, joinery workshops and agricultural buildings rated IP65. Elektra V is designed to withstand vibrations on ships and offshore platforms and is approved by Det Norske Veritas. Available for single and 3 phase systems, 50 or 60Hz and rated IP44. Elektra H is designed for rooms with high temperatures, up to 70 °C and is rated IP44.

  • Unit Heater Types – ATEX Rated Heaters

    Unit Heater Types - ATEX rated

    Heater with ATEX rated fan

    These heaters can be installed where potentially explosive gases may be present. They are suitable for Zone 1 and Zone 2 hazardous areas and for gas groups 11A and 11B. They must be mounted horizontally and operated where the ambient temperature does not exceed 40 C. The heaters are stamped T3 and can be used in areas designated T1, T2, or T3. These heaters are widely used in installations such as oil refineries, waste water treatment plants and paint storage areas. ATEX certified with robust 2mm thick epoxy coated steel cabinet, adjustable air direction louvres, over temperature protection, vacuum charged fluid-to-air heat exchanger  and built-in contactor.


  • Unit Heater Types – Oil, Diesel, LPG and Propane Fired Heaters

    Unit Heater Types - Marquee Heater

    Marquee packages can be Diesel, Oil, or Gas powered.

    Unit Heater Types - Duct Adaptor


    These are available in both fixed and mobile designs. For fixed systems it is likely that a large external fuel storage facility would be provided to facilitate economical bulk fuel deliveries. Mobile systems often include a small built-in fuel cell. Mobile systems are partticularly applicable to construction sites where permanent electrical connections are yet to be completed or for ‘Marquee’ events such as temporary concert venues, festival arenas, large weddings and other similar applications. A single heater may be ducted to multiple areas using a variety of duct-adaptors.

    Unit Heater Types - Oil Fired HeaterIndirect Oil Fired Heaters have become increasingly popular in recent years; designed for horizontal or vertical suspension, the units are used extensively in horticultural and agricultural applications, and are often used in conjunction with suspended, perforated ducting, for maximum heat penetration. These units can also be floor mounted, using an optional trolley kit is available to facilitate movement between sites. The pictured unit has an output of 81kW (280,000 BTUs / Hr), with an airflow of 7,100 m³ / Hr.


  •  Unit Heater types – Solid Fuel Heaters

Unit Heater Types - Solid Fuel Heater

Solid fuel Unit Heater

Ideal for industrial situations which produce large amounts of combustible waste. The heater pictured is designed to burn waste wood or logs to produce industrial quantities of heat delivered onto an air flow via its integral heat exchanger. The result is a space heater that looks a bit like a cross between a large wood stove and a conventional ‘bullet’ style space heater. Once installed will provide years of heat from waste wood for the cost of powering the fan.The tube heat exchanger in the top of the heater ensures that once lit, heat can be delivered quickly and easily on the air flow through the tubes. Fitted with a centrifugal fan it is suitable for connection of ductwork, to distribute warmed air to specific locations or even through to adjacent rooms.

  • Unit heater Types – Biomass Heaters.

Unit Heater Types - Biomass heater

Biomass Unit Heater

These are totally self-contained systems which are ideal for space heating industrial type environments. They run on biomass pellets and the pictured range has nominal heat outputs ranging from 43 to 300 kW. Each system has 5 principal parts; The burner housing and combustion chamber; An automatic pellet burner; Control panel and burner programmer; Pellet screw conveyor; Pellet container tank. The combustion chamber with piped exchanger is designed to achieve performances higher than 92%. The pellet container which may be attached to either side of the heater has a standard capacity is 190kg but larger capacity containers are available if required.

  • Unit Heater Types – Cabinet Heaters.

Unit Heater Types - Cabinet Heater

Cabinet Unit Heater

There is a huge range of cabinet heaters on the market with a variety of fuels and electrically driven fans. The pictured heater is in fact oil-fired and is supplied with an integral day-tank and power cord enabling plug-and-play operation in both fixed and temporary applications.


  • Unit Heater Types – Sizing Your System.

Selection of the most applicable size and quantity of Unit Heaters to gain optimum cost effectiveness in any particular situation is complex. There are a number of other variables that contribute to the overall calculation including:-

  • Ambient temperature outside

    Unit Heater Types - Destratification fan

    Destratification Fans will add to Unit Heater efficiency in high ceilinged buildings

  • Materials of construction and how well insulated the building is
  • The efficiency of the heating system
  • The control accuracy of the heating system
  • Fuel preference
  • The height of the space to be heated will determine whether destratification fan(s) would add to overall efficiency

Help and advice

If you would like to find out more or to get advice on reaching an ideal air circulation system for your application then email us at puravent@gmail.com or call us on +44 (0)1729 824108