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Mr. Heater Big Maxx vs Modine Hot Dawg vs Reznor Reviews

⭐ Best Overall ⭐🥈 Runner-Up 🥈💵 Best Value 💵
Modine HD45AS0111Natural Gas Hot Dawg Garage Heater 45,000 BTU with UDAP-045 - Reznor Gas Furnace Hanging Unit Heater Mr. Heater F260550 Big Maxx MHU50NG Natural Gas Unit Heater,Black
Modine Hot DawgReznor UDAP-045Mr. Heater Big Maxx

The best way to keep your garage warm is with a natural gas heater. There are many to choose from, but we narrowed it down to our top three. We considered price, heat output, build quality, and user reviews to find the best of the best.


The Modine Hot Dawg is usually mentioned right alongside the Mr. Heater Big Maxx when talking about the best natural gas garage heater. It may be more expensive, but it’s a reliable, high quality heater that gets the job done.


The Hot Dawg heater measures 26 ¾” x 22” x 12 ¼” and weighs 60 lbs. It’s flatter, wider, and less boxier than the Big Maxx. It’s silver in color and has an industrial look to it.

Next to the ‘Hot Dawg’ logo on front is the heating vent with three adjustable louvers. On the back of the unit is a 3” flue transition piece, a cutout for the gas pipe, a cut out for electrical, and a large fan with a finger-proof guard.

By using a 3” vent pipe instead of a 4” pipe like the other two heaters, the Hot Dawg simplifies side-wall or roof venting. The smaller the hole you need to cut in your house, the better.


The Modine Hot Dawg is shipped to run on natural gas but can run on liquid propane with a conversion kit (sold separately). If you’re going to be using propane, you should contact the seller and ask if they will ship you a propane-fitted heater instead. Some of them keep both in stock and will be more than happy to oblige. Not only will this save you installation time, but money as well, as you won’t need to purchase a conversion kit.

Producing 45,000 BTU/hr, the Hot Dawg is capable of heating a space up to 1,125 square feet. It’s not quite as powerful as the Big Maxx, but unless you’re really pushing the limits of the heater you won’t notice it. It produces plenty of heat for a two or three car garage and has no problem heating your space, even if it’s uninsulated.


Modine provides two mounting brackets that need to be installed to the heater before hoisting it up. You can either install them left side control access or right side control access. Because you only need 1” of clearance, mounting it directly to the ceiling saves space and keeps the heater out of the way.

If you would like more ceiling clearance then you’re also able to suspend the heater by lag bolts or threaded rods. Suspending the unit from the ceiling also has the added benefit of reducing vibrations and noise caused by vibrations.


With so many products being made overseas nowadays, it’s refreshing to see that the Modine Hot Dawg is made right here in the USA with high quality materials.

The casing is made of solid, heavy gauge metal for maximum durability and the motor is permanently lubricated for maintenance-free dependability.

As with any product, there’s always risk of receiving a defective unit. Luckily, that risk is very small when it comes to the Modine Hot Dawg. Should anything happen with your heater, Modine offers a 10 year limited warranty on the heat exchanger, plus whatever return window you have from where you purchased it from.

✅ Permanently lubricated motor for maintenance-free operation❌ Expensive
✅ Quiet operation
✅ Natural gas and liquid propane fuel options
✅ Durable construction made from heavy gauge metal
✅ Finger-proof fan guards
✅ 10 Year limited warranty

Heat: 45,000 BTUs
Dimensions: 26 3/4″ x 22″ x 12 1/4″
Weight: 60 lbs


Reznor is a brand that is not as well-known to consumers as Mr. Heater or Modine, but they are pioneers in the heating industry. They released the first high efficiency heater 20 years before their competitors.

Reznor heaters are known for their innovative design, their extensive field tests, and their high quality construction. The UDAP-045 is their power-vented model that’s perfect for garages and small shops.


Like all of Reznor’s heaters, the UDAP-045 is built with a solid, clean exterior. Its two-tone color design and high gloss shine stands out from others, and the mitered corner bearing their name adds to the look of professionalism.

Measuring in at 26 5/8” x 26” x 12 1/8” and weighing 59 lbs, it’s similar in size and weight to the Modine Hot Dawg. Its low-profile design keeps the heater up and out-of-the-way in order to maximize garage space.

On the back of the heater is a large fan with a finger-proof guard, a 4” flue transition piece, a gas inlet, and a cut-out for electrical.


The UDAP series heaters are fitted to run on natural gas, but a liquid propane conversion kit is available. Having the option of two fuel sources is important in case you don’t have a natural gas line connected to your home or you don’t want to run a line to your heater.

The UDAP-045 produces 45,000 BTU/hr of heat and will heat a garage or shop with ease. The heating process is as follows:

  1. Call for heat
  2. Prepurge
  3. Ignition trial period
  4. Fan/blower ON delay
  5. Steady Heat
  6. Post-purge
  7. Fan/blower OFF delay

Should the unit overheat, the gas supply control system will cut the gas, acting as a safety shutoff switch.


For best results, the heater should be mounted at least 8 feet off the ground. If you’re installing it in a garage with standard ceilings, you’ll need to avoid suspension rods and mount it directly to the ceiling using either their low-ceiling suspension kit or a Quick-Sling quick swivel kit.

When mounted at 8 feet, the UDAP-045 can throw heat up to 33 feet. If mounted at 12 feet, it can throw heat up to 27 feet. With such a powerful throw, heat easily circulates throughout the space to heat the area as evenly as possible.

When choosing a location to mount the unit, it’s important to remember that the heater is most effective when it’s located as close to the work area as possible without directly blowing onto the occupants. If you decide to mount the unit in the center of the ceiling, the heat should be directed towards exposed walls in order to reflect it and circulate back into the room. If there is a source of cold air infiltrating the room, such as an entryway, then the heat should be directed towards the cold airflow.


Enough can’t be said about the quality of parts Reznor uses in their heaters. They’re built for industrial use and are made to last. Not only that, but they look great too.

Reznor offers a 10 year warranty on the heat exchanger and a 5 year warranty on everything else. That’s the best on our list.

As mentioned earlier, Reznor is not well-known in the residential market. Their forte is in the industrial market where quality and efficiency are the two most important factors. They’ve been ahead of the curve for years and the UDAP series is another example of why they’re one of the best in the business.

✅ Industry-leading heating company❌ Expensive
✅ High quality parts and first-class construction❌ Not sold in most stores
✅ Aesthetic design with two-tone colors and high gloss paint
✅ Built-in suspension points for threaded rod
✅ Wind tunnel tested louvers for maximum air flow

Heat: 45,000 BTUs
Dimensions: 26 5/8″ x 26″ x 12 1/8″
Weight: 59 lbs


Mr. Heater is a big name in the heating industry, and the Big Maxx is one of their best selling products. It’s very similar to the other two heaters on our list but costs just half the price. With such an affordable way to heat your garage, it’s no wonder it’s one of the most popular garage heaters on the market.


The Mr. Heater Big Maxx measures 25” x 18 ½” x 17”, weighs 70 lbs (the heaviest heater on our list), and comes in a neutral beige color. It’s designed to be installed in low-ceiling buildings and garages.

To the right of the ‘Mr. Heater Big Maxx’ logo on the front is the vent where the heat comes out. The louvers can be adjusted to direct heat upwards, downwards, or straight ahead. If the heater is installed in an inverted position, the louvers can also be reinstalled in an inverted position to match the heater.

The back of the unit has an attached 4” flue transition piece, a ½” gas inlet, electrical inlets, thermostat wiring posts, and a fully enclosed direct drive fan for safety.


The Big Maxx runs on either natural gas or liquid propane. It ships ready for natural gas, but comes with a conversion kit if you would rather use propane.

Its 50,000 BTUs can heat up to 1,250 square feet, which is optimal for a two or three car garage or a small shop. It’s capable of heating larger areas like a four car garage or a mid-sized shop, but it will take a bit longer to warm up.

When you’re ready to heat your garage or workspace, simply turn on your thermostat (sold separately) to the desired temperature. The combustion air blower will start immediately. After about 30 seconds, the automatic spark ignition lights the gas and starts the heater. Depending on the size of your space and the current temperature, your garage will heat up in about 15 – 30 minutes.

If you live in a high altitude area 2,000 ft or more above sea level, you may need to manually adjust the manifold pressure on the heater.


The Mr. Heater Big Maxx comes ready for installation. It includes two angled brackets that can either be mounted directly to the ceiling joists or to support rods (not included) which are then mounted to the joists.

The Big Maxx can also be installed in an inverted position if you’re having issues lining up your pipe fittings and venting system. Just be sure to invert the louvers if you install the unit upside-down, otherwise the heat may blow towards the ceiling.


The Mr. Heater Big Maxx costs about half of the price of the Reznor UDAP-045 or the Modine Hot Dawg, but unfortunately, some corners had to be cut to achieve this.

Some buyers reported having problems with the control board, the fan making a loud rattling sound, or the heater arriving damaged. Fortunately, Amazon is great with returns and they will replace your heater should you have any problems. You won’t be out any money if you receive a defective product, though you may be out the time it took to install it.

We think the price far outweighs any quality issues the heater may potentially have, but ultimately, that’s for you to decide.

✅ Very affordable❌ Lower quality parts that are prone to failure
✅ 50,000 BTU/hr❌ Loudest heater of the three
✅ Comes with fuel conversion kit❌ Boxy design
✅ Mounting hardware included
✅ 1/2″ gas inlet on back for easy installation

Heat: 50,000 BTUs
Dimensions: 25″ x 18 1/2″ x 17″
Weight: 70 lbs

Installation Guide

hammer and tool belt


When choosing an installation location, there are a few things to keep in mind:

  1. Electrical Outlets. Most garages will have at least one electrical outlet located on the ceiling and a few on the wall, so be sure to keep that in mind when mounting your heater. The last thing you want is to have to run an extension cord across the garage, or worse, run electrical to your heater.
  2. Gas Line. As with the electrical outlets, you’ll need to be mindful of where your gas line is. There’s no getting around piping your gas line to your heater, but you can make it easier on yourself by being aware of where your gas line is in relation to your garage. It should go without saying that the shorter the run, the better.
  3. Garage Door Clearance. It seems obvious, but you’d be surprised how many people have installed one of these heaters with their garage doors closed, only to find out that it’s in the way of the garage door track.

We’ve found that the best location for these heaters is in either corner of the garage closest to your house and installed at an angle. This allows for maximum air flow and coverage.

They must be mounted to the ceiling with at least an 8 ft. clearance from the ground. Not only will it distribute heat better, but it can be very dangerous to have the heater on the floor with vehicles coming in and out of the garage. One small accident and you risk not only damaging the heater, but breaking the gas line as well, causing a dangerous gas leak.


Mounting a garage heater to the ceiling can be challenging if you don’t know what to do. With the right tools and information, you’ll be able to mount and install it yourself with ease.

  1. Attach the mounting brackets to the heater.
  2. If installing on an angle, attach a couple of 2x6s to the joists with lag screws at a 45º angle.
  3. Wrap a couple of cargo straps around the heater.
  4. Use a locking hoist to raise the unit to the ceiling.
  5. Attach the unit to the 2x6s using carriage bolts.


Natural gas heaters require ventilation to the outside. All three heaters are rated Category 1 for vertical ventilation and Category 3 for horizontal ventilation.

Category 1 is negative pressure, meaning that if there are any leaks in the venting system, air from the garage will flow into the flue, preventing any harmful gas from leaking into the garage. Category 1 venting can be single-wall, double-wall, or B-vent.

Category 3 is positive pressure, meaning that any leaks in the flue will cause harmful gas to flow into the garage. Because of the added risk, Category 3 venting requirements are much stricter. They require gas-tight seams, a minimum thickness, and corrosion resistant material.

An important thing to keep in mind when installing the ventilation system is to keep your vent runs as short as possible while limiting the number of elbows used.

Below is a great ventilation installation tutorial. He installs a Modine Hot Dawg, but the information can be applied to all three heaters on our list. Please note that the Hot Dawg has a 3” vent connection while the Reznor and Big Maxx have a 4” vent connection.

The video below shows how to install a Modine Hot Dawg, but the information can be used to install any of the heaters on our list:

Gas Line

Running the gas line will be the most difficult part of this project. You should hire a professional if you aren’t comfortable doing it yourself.

Before getting started, make sure you shut off the gas. You’ll need to find the best (and shortest) route to run your gas line to the heater. Run it along the wall and get it close enough to the heater so that you can install a flex line.

Before you install the flex line, use a manometer to check for any leaks in the line. If there are no leaks, install the flex line to finalize the gas installation.

Check out the video below for the basics of installing gas pipes:


All of the heaters on our list require a ‘heat only’ thermostat of your choice. Luckily, this is the easiest part of the installation process.

You’ll want to follow the instructions that come with your thermostat, but basically, you’ll want to do the following:

  1. Connect red wire and white wire to each terminal on the thermostat
  2. Mount the thermostat to the wall away from the heater’s airflow
  3. Run the wires to the heater
  4. Connect red wire and white wire to each terminal on the heater

The following video will show you the basics of installing a thermostat:


Comparison Table

We scoured user manuals, specification sheets, user reviews (and more) in order to put together a comparison table to help you make the most informed buying decision.

⭐ Best Overall ⭐🥈 Runner-Up 🥈💵 Best Value 💵
Modine HD45AS0111Natural Gas Hot Dawg Garage Heater 45,000 BTU with UDAP-045 - Reznor Gas Furnace Hanging Unit Heater Mr. Heater F260550 Big Maxx MHU50NG Natural Gas Unit Heater,Black
ProductModine Hot DawgReznor UDAP-045Mr. Heater Big Maxx
Overall Rating969389
Price$ $ $ $$ $ $ $ $$ $
Size (L x W x H)26 3/4” x 22” x 12 ¼”26 5/8″ x 26″ x 12 1/8″25” x 18 ½” x 17”
Weight60 lbs59 lbs70 lbs
Fuel TypeNatural Gas or Liquid Propane (with kit)Natural Gas or Liquid Propane (with kit)Natural Gas or Liquid Propane (with kit)
Fuel Conversion KitSold SeparatelySold SeparatelyIncluded
Heat TypeForced AirForced AirForced Air
ThermostatSold SeparatelySold SeparatelySold Separately
BTU Input45,000 BTU45,000 BTU50,000 BTU
BTU Output36,900 BTU37,350 BTU40,000 BTU
Heating Efficiency82%83%80%
Heating Area (Uninsulated)1,125 Sq. Ft.1,125 Sq. Ft.1,250 Sq. Ft.
Heating Area (Insulated)1,350 Sq. Ft.1,350 Sq. Ft.1,500 Sq. Ft.
Powered ExhaustYesYesYes
Entering Airflow (CFM)720629N/A
Outlet Velocity (FPM)725656N/A
Heat Throw (Mounted @ 10 Ft.)27 Ft.33 Ft.N/A
Venting Requirements)Vertical (Category 1), Horizontal (Category 3)Vertical (Category 1), Horizontal (Category 3)Vertical (Category 1), Horizontal (Category 3)
Vent Connection)3”4”4”
Mounting HardwareIncludedSold SeparatelyIncluded
Ceiling & Side Clearance1”1”1”
Access Panel & Rear Clearance18”18”18”
Gas Connection½”½”½”
IgnitionDirect Spark Ignition (Electric)Direct Spark Ignition (Electric)Direct Spark Ignition (Electric)
Safety Shut-offYesYesYes
Installation LocationResidential, Commercial, & IndustrialResidential, Commercial, & IndustrialResidential, Commercial, & Industrial
Warranty10 Year Limited
(heat exchanger)
10 Year Limited
(heat exchanger, burner, flue box)

5 Year Limited
(electrical & mechanical components)
10 Year Limited
(heat exchanger)

3 Year Limited
(parts & burner)
Country of ManufactureUSAUSA & EuropeN/A


We hope that this review has helped you find the best natural gas garage heater. As you can see, we’ve narrowed it down to three great heaters to choose from, each with their own unique features.

The best overall is the Modine Hot Dawg. It’s very quiet, has a durable metal shell, and comes with a great warranty.

The next best thing is the Reznor UDAP-045. It’s built with high quality parts, has a great looking design, and it’s been wind tunnel tested for maximum air disbursement.

The best bang for your buck is the Mr. Heater Big Maxx. It’s affordable, puts out 50,000 BTU/hr, and comes with a fuel conversion kit.

Thanks for reading and stay warm out there!