Guide to the UNIMAC 20kW Diesel Heater: Suitability, Safety and Key Considerations for Large Spaces

UNIMAC UMDHT-58 MkII 20kW Diesel Heater Guide

The UNIMAC UMDHT-58 MkII is a portable forced-air combustion heater intended to produce a large amount of heat quickly in appropriately ventilated work areas.

Its current published specifications include 20kW heat output, 550m³/h airflow, a 19-litre fuel tank and maximum fuel consumption of 1.9 litres per hour.

Those figures may make it appealing for workshops, construction areas, agricultural buildings and other large spaces, but there is a critical point that matters more than heating capacity:

This heater burns fuel and produces combustion gases.

It must not be treated like an ordinary electric fan heater. Carbon monoxide, combustion air, ventilation, hot surfaces, fuel handling and fire separation all need to be considered before use.

Testing statement: Firebusters has not personally tested this heater. Specifications and safety information are based on current supplier information and the UNIMAC instruction manual checked in September 2026.

Critical Carbon Monoxide Warning

Carbon monoxide cannot be seen or smelled and can cause serious injury or death.

The UNIMAC manual specifically warns that direct-fired heaters can cause carbon-monoxide poisoning when used incorrectly, including indoors without adequate air circulation.

The manual also states:

• adequate combustion and ventilation air must be provided;
• the heater is not for home use;
• the heater is not for recreational-vehicle use;
• flammable vapours and combustible airborne material must be kept away; and
• failure to follow the safety instructions can result in fire, explosion, burns, asphyxiation, carbon-monoxide poisoning or electrical shock.

Do not use this heater in a closed room, home, caravan, small shed, office or other inadequately ventilated occupied space.

UNIMAC UMDHT-58 MkII Product Overview

Verified Specifications

Direct-Fired or Indirect-Fired? Documentation Conflict

There is an important naming inconsistency in online documentation.

The current Edisons catalogue describes this model as a direct forced-air space heater, while some older URLs and reseller titles use the term “indirect”.

The UNIMAC manual itself contains a specific warning about direct-fired heaters producing carbon monoxide when incorrectly used.

The UMDHT-58 MkII also does not have the separate flue arrangement normally expected of a true indirect-fired heater that keeps combustion gases separate from the heated air.

Do not install improvised exhaust ducting or a flue onto the heater unless the manufacturer has specifically approved it.

What Does 20kW Heating Capacity Mean?

Twenty kilowatts is the heater’s published heat-output rating.

The supplier also advertises a suggested heating area of approximately 220–300m².

That area figure should be treated as a broad marketing guide rather than a guarantee.

How effectively any heater warms a building depends on:

• ceiling height;
• building volume;
• outdoor temperature;
• insulation;
• air leakage;
• doors opening and closing;
• ventilation rate;
• wind exposure; and
• how quickly heat is lost through the building fabric.

There is an obvious trade-off with a combustion heater: enough fresh air must be supplied for safe operation, but that ventilation can also allow heated air to escape.

Do not size a workplace heater purely from floor area.

Fuel Consumption and Runtime

The UMDHT-58 MkII has a 19L fuel tank and maximum published fuel consumption of about 1.9L per hour.

At that consumption rate, a theoretical full-tank runtime is around 10 hours, which matches the supplier’s published figure.

Actual runtime can vary with thermostat cycling, operating conditions and usable fuel remaining in the tank.

Do not refuel the heater while it is operating or while hot.

Allow it to cool and follow the manufacturer’s refuelling instructions.

Fuel should be stored safely away from ignition sources and the heater itself.

Diesel or Kerosene?

Current supplier information lists the UMDHT-58 MkII as compatible with both diesel and kerosene.

That does not mean petrol, solvents, thinners or other flammable liquids can be substituted.

The manual warns against using or storing gasoline and other flammable vapours and liquids near the heater.

Use only fuel specifically approved for the exact heater and follow the manufacturer’s fuel-quality and storage instructions.

Ventilation Is a Safety Requirement, Not an Optional Comfort Feature

This heater consumes oxygen and releases combustion products.

The UNIMAC manual specifically states that unvented portable heaters use oxygen from the area in which they operate and that adequate combustion and ventilation air must be provided.

A partially open roller door or window should not automatically be assumed to provide enough ventilation for every building.

Required ventilation depends on factors including:

• heater output;
• building volume;
• natural air leakage;
• number of occupants;
• other combustion equipment;
• doors and windows;
• mechanical extraction; and
• duration of operation.

For workplace use, ventilation design and exposure control may need assessment by a competent person.

Carbon Monoxide Detection Does Not Replace Ventilation

A suitable carbon-monoxide alarm can provide an additional warning layer where combustion appliances are permitted to operate.

It does not make an unsafe location safe.

CO alarms should not be used as a substitute for:

• adequate fresh-air supply;
• proper heater maintenance;
• correct fuel combustion;
• workplace risk assessment; or
• manufacturer ventilation requirements.

If anyone develops headache, dizziness, nausea, weakness or confusion around combustion equipment, leave the area and seek appropriate assistance.

Workplace Diesel-Emission Exposure

Carbon monoxide is not the only potential air contaminant from diesel combustion.

Diesel emissions can contain gases and particulate matter that present respiratory and longer-term health risks.

Safe Work Australia published updated guidance in 2026 on managing workplace exposure to diesel engine emissions and airborne contaminants.

In workplaces, risk controls may involve:

• eliminating or reducing combustion sources;
• local exhaust ventilation where applicable;
• adequate general ventilation;
• maintenance;
• air monitoring where necessary; and
• professional occupational-hygiene advice for higher-risk environments.

Simply being in a large shed does not automatically prove contaminant levels are safe.

Safety Cut-Outs

The supplier lists several protection features for the UMDHT-58 MkII:

• flame-out protection;
• overheat protection; and
• electrical fault/power protection.

These protections are valuable, but they do not remove the need for ventilation, fuel safety, supervision or correct clearances.

A failed flame, blocked fuel system or overheating fault should be investigated before returning the heater to service.

Electrical Supply and RCD Protection

Although diesel supplies the heat, the fan, ignition and controls depend on mains electricity.

The published specification is:

• 240V;
• 50Hz;
• 230W electrical motor; and
• Australian standard plug.

The UNIMAC manual specifically requires residual-current protection and says damaged power cables must not be used.

Keep the power connection:

• away from water;
• away from hot surfaces;
• away from vehicle traffic;
• protected from crushing; and
• positioned so it does not become a trip hazard.

Unplug the heater before servicing.

The Front Outlet Gets Extremely Hot

The manual warns that the heater’s front outlet becomes extremely hot during operation.

That creates both burn and fire risks.

Never point the hot-air outlet directly at:

• timber stored close to the heater;
• cardboard;
• plastic sheeting;
• fuel containers;
• paint or solvent containers;
• clothing;
• people; or
• other combustible materials.

Allow the heater to cool completely before handling or storing it.

Clearances: Do Not Invent a Distance

The accessible manufacturer material reviewed by Firebusters warns users to maintain safe separation from combustible materials but does not provide a reliable model-specific numerical clearance table in the text available to us.

For that reason, this guide deliberately does not publish a guessed distance such as one metre or two metres.

Check the label and current full manual supplied with your exact heater for front, side, rear and overhead clearances before operation.

If that information cannot be found, obtain it from the supplier before using the unit.

Do Not Use Near Flammable Vapours or Combustible Dust

The manual warns against operating the heater where volatile or airborne combustible substances may be present.

Examples can include:

• petrol vapour;
• solvents;
• paint thinner;
• flammable aerosols;
• some dust clouds; and
• unknown chemicals.

This matters in workshops where painting, solvent cleaning, fuel handling, sanding or other processes may occur near the heating area.

Do not assume that a large shed is automatically safe merely because there is space around the heater.

Is It Suitable for a Workshop?

The supplier markets the heater for areas such as workshops, warehouses and agricultural applications where appropriate ventilation is available.

The manual, however, contains strong warnings around carbon monoxide and also states that it is not for home or recreational-vehicle use.

Firebusters therefore would not describe it as universally suitable for indoor workshops.

Suitability depends on the actual building, its ventilation, occupancy and workplace controls.

A fully enclosed mechanics workshop with all roller doors shut is a very different environment from an open-sided construction area.

Homes, Garages and Caravans

This is not a residential room heater.

The manufacturer’s manual specifically says it is not for home or recreational-vehicle use.

Firebusters would not recommend using it to heat:

• a house;
• bedroom;
• living room;
• closed garage;
• caravan;
• campervan;
• tent; or
• other sleeping space.

Choose a heating system specifically approved for the intended residential or recreational application instead.

Portability

The 20kW model weighs approximately 14kg and measures about 31 × 75 × 42cm.

It has an integrated carrying handle, making it considerably more portable than permanently installed space-heating equipment.

The 20kW specification does not list the transport wheels fitted to some larger UNIMAC heater models.

Always switch the unit off, disconnect power and allow it to cool before moving it.

76dB Published Noise Level

The supplier lists a sound rating of approximately 76dB.

That means this is not intended to be a silent room heater.

In a workplace, total noise exposure depends on the heater plus every other noise source and the amount of time workers spend nearby.

Where occupational noise may be an issue, assess the complete work environment rather than relying on a single product figure.

Who Does This Heater Suit?

Potentially suitable for:

• open or appropriately ventilated construction areas;
• appropriately assessed workshops;
• agricultural work areas;
• large maintenance areas; and
• temporary worksite heating where combustion heating is permitted.

Not suitable for:

• homes;
• caravans or recreational vehicles;
• sleeping areas;
• closed sheds;
• poorly ventilated workplaces;
• areas containing flammable vapours or combustible dust; or
• sites where ventilation and combustion-air requirements cannot be maintained.

Pre-Use Safety Checklist

Firebusters Practical Recommendation

The UMDHT-58 MkII provides substantial portable heating capacity in a relatively compact 14kg package.

Its 20kW output, 550m³/h airflow and 19L fuel tank can make sense for suitably ventilated large work areas where a direct combustion heater is appropriate.

But ventilation should be the deciding factor before heating capacity.

If you cannot confidently establish safe combustion air, ventilation, clearances and workplace exposure controls, choose a different heating method rather than relying on this heater.

Frequently Asked Questions

What is the exact model?

UNIMAC UMDHT-58 MkII, SKU UMDHVP03A.

How much heat does it produce?

The published heating output is 20kW.

How much air does it move?

The current supplier specification lists approximately 550m³ per hour.

How much diesel does it use?

Maximum published fuel consumption is approximately 1.9 litres per hour.

How large is the tank?

Approximately 19 litres.

How long will one tank last?

The supplier publishes approximately 10 hours. Actual runtime can vary with operation and thermostat cycling.

Can it use kerosene?

The current supplier specification lists both diesel and kerosene as compatible fuels.

Can I use it inside my house?

No. The UNIMAC manual states that the heater is not for home use.

Can I use it in a caravan?

No. The manual specifically says it is not for recreational-vehicle use.

Can I use it in a workshop?

Only where the specific workplace has adequate combustion air and ventilation and the heater is appropriate under the site’s risk controls. Do not assume every workshop is suitable.

Does it have carbon-monoxide protection?

The supplier lists flame-out and overheat protection, but that does not eliminate carbon-monoxide risk. The manual still requires adequate ventilation.

Does it need electricity?

Yes. The fan, ignition and controls require 240V/50Hz electricity. The published electrical motor input is 230W.

Does it need an RCD?

The UNIMAC manual calls for residual-current protection in the electrical system.

What clearances are required?

Follow the exact clearance requirements printed on the current heater and supplied manual. Firebusters has not published a guessed numerical clearance because a reliable model-specific table was not available in the material reviewed.

Sources

• 
  Edisons – UNIMAC Heater Range
  
• 
  Mytopia – UNIMAC UMDHT-58 MkII Specifications
  
• 
  UNIMAC UMDHT-58 MkII Instruction Manual
  
• 
  Safe Work Australia – Managing Diesel Emission Risks
  

Specifications and supplier availability may change. Information checked September 2026.