Modine HD75 Unit Heater

Do you need serious, reliable heat for a large greenhouse, garage or workshop? Then the Modine HD75 Unit Heater is built for the job. It’s the largest model in the low-profile Hot Dawg range, with a powerful 75,000 BTU input. Above all, it delivers strong, even heat across a big space. So your plants — or your work — stay comfortable right through the colder months.

Modine has built quality unit heaters since 1916, and the HD75 lives up to that name. For example, it uses a tough aluminised-steel heat exchanger, backed by a 10-year warranty. In addition, a sealed, permanently-lubricated motor keeps it running dependably for years. So it’s a heater you can install once and rely on for the long haul. Plus, you can choose natural gas or propane to suit your site.

Why Choose the Modine HD75

The HD75 combines big-space power with a compact, tidy design. To start, it produces 61,500 BTU of output at 82% thermal efficiency. So it warms a large area economically. In addition, the propeller fan pushes warm air well out across the space, heating it quickly and evenly. As a result, it’s ideal for a large garage, workshop, or a greenhouse up to around 60m².

It’s also designed to be easy to live with. For example, the low-profile cabinet mounts close to the ceiling on the included brackets, so it keeps your floor clear. In addition, it runs quietly, so it won’t disturb your work. Plus, the gas, electrical and flue connections can be reversed by flipping the unit. So it suits left- or right-hand installation. Better still, you can specify an optional stainless steel heat exchanger — a smart upgrade for the humid, corrosive environment inside a greenhouse.

H2: Key Features

• The largest low-profile Hot Dawg — 75,000 BTU input / 61,500 BTU output
• 82% thermal efficiency for economical heating
• Heats a large garage, workshop or greenhouse up to ~60m² (650 sq ft)
• Quiet operation
• Low-profile design mounts close to the ceiling
• Ceiling mounting brackets included
• Available in natural gas or propane
• Optional stainless steel heat exchanger for humid/corrosive spaces
• Reversible gas, electrical and flue connections (left or right hand)
• Power-vented exhaust uses small-diameter (3″) vent pipe
• Tough aluminised-steel heat exchanger
• 10-year heat-exchanger warranty (2 years parts)

H2: Specifications

• BTU input: 75,000 BTU/hr
• BTU output: 61,500 BTU/hr
• Thermal efficiency: 82%
• Suits spaces up to: ~60m² (650 sq ft) greenhouse, or a large garage
• Fuel: natural gas or propane (LPG)
• Heat exchanger: aluminised steel (stainless steel optional)
• Vent size: 3″ (~75mm)
• Mounting: ceiling brackets included
• Weight: approx. 39kg (85 lb)
• Warranty: 10-year heat exchanger, 2-year parts

Browse our full greenhouse heating and climate-control range and greenhouse accessories, or speak with our team for help sizing the right heater for your space.

H2: Which Hot Dawg Size? HD45 / HD60 / HD75 / HD125

Choosing the right output is the key to efficient, even heat, so it helps to compare. The HD45 (45,000 BTU) suits a small greenhouse or 2–2½ car garage. The HD60 (60,000 BTU) is the mid-size choice for a space up to ~50m². The HD75 (75,000 BTU) is the largest low-profile model — ideal for a large garage or a greenhouse up to ~60m². The HD125 (125,000 BTU), by contrast, is a higher-mounting unit for large commercial greenhouses and warehouses. So match the model to your space: too big, and it short-cycles; too small, and it struggles. Not sure? Then talk to our team for sizing help.

H2: Natural Gas or Propane — and Why Stainless?

The HD75 comes in two fuel types, so pick what suits your site. Natural gas is convenient where you have a mains connection. Propane (LPG) suits sites without mains gas — common in rural and off-grid locations. In addition, you can upgrade to a stainless steel heat exchanger. This is well worth considering for a greenhouse, because the warm, humid, sometimes chemically treated air can corrode standard steel over time. So stainless adds real longevity in that environment.

H2: Installation, Gas and Safety (Australia)

This part is important, so please read it carefully. The HD75 is a vented gas appliance, so it must be installed by a licensed gasfitter in line with Australian gas-installation requirements. In addition, gas appliances in Australia must meet the relevant Australian Standards and certification. So before you buy, confirm that the unit and its configuration are approved for use and sale in Australia. Please also check the electrical supply (the standard US model is 115V), and make sure it suits Australian power or that you have the correct variant. Finally, the unit needs adequate combustion-air ventilation and correct flue venting — another reason professional installation is essential.

For authoritative guidance, your state energy safety regulator (for example, Energy Safe Victoria or NSW Fair Trading) and the relevant gas technical regulator set the rules for gas appliance installation. So always check current requirements before installing. We’re happy to help confirm the right specification for your project.

H2: Frequently Asked Questions

What size space does the HD75 heat? With 75,000 BTU input and 61,500 BTU output, it suits a large garage, a workshop, or a greenhouse up to around 60m² (650 sq ft).

How is it different from the HD60 and HD125? The HD75 is the largest low-profile Hot Dawg. The HD60 (60,000 BTU) is the mid-size model, while the HD125 (125,000 BTU) is a higher-mounting unit for large commercial spaces.

Can it run on propane? Yes. It’s available in natural gas or propane (LPG), so you can match it to your site — handy for rural and off-grid locations.

What’s the stainless steel option for? A stainless steel heat exchanger resists corrosion from the warm, humid greenhouse environment. So it’s a smart upgrade for longevity in a greenhouse.

Does it need professional installation? Yes. As a vented gas appliance, it must be installed by a licensed gasfitter in line with Australian requirements.

H2: Conclusion

In the end, the Modine HD75 Unit Heater is a powerful, efficient and dependable way to heat a large greenhouse, garage or workshop. It combines strong 75,000 BTU output, a low-profile design with brackets included, quiet operation, fuel and stainless-steel options, and a 10-year heat-exchanger warranty. Plus, with professional installation, it’ll keep your space warm for years. So browse our heating range or get in touch for expert sizing and supply advice today.