What Size Rinnai Direct Vent Heater Do I Need?

No matter how quick you want to keep your home warm, buying a Rinnai propane heater should never be an impulsive purchase.

These types of heaters are expensive, long-term commitments that have significant implications on your heating bill and comfort levels alike, which is why it’s important to do your research before installing one.

What Size Rinnai Direct Vent Heater Do I Need?

You can determine the right size by multiplying the square footage by the BTU per square foot to arrive at the total BTU rating you’ll need from your Rinnai heater. For example, a 1000 square feet room will need a 20,000 BTU Rinnai heater. But other considerations, such as ceiling height, number of people occupying the room, size of your windows and doorways, might call for more heating power.

Why Sizing is Important

Adding a wall furnace to your space can provide you with a wealth of warmth during the winter months.

However, if your wall furnace is not properly sized, you may wind up paying more while still being uncomfortable.

A popular, misguided way of picking a wall furnace is to use simple rule-of-thumb sizing approaches like calculating square footage.

Unfortunately, plenty of other factors may influence your BTUs significantly, such as the weather and building design.

Aside from getting a complete sizing estimate of your space, your best bet is using an online wall furnace sizing.

If your wall furnace happens to be too small, it’s bound to run constantly while trying to meet the demand. However, it will never get the room temperature that you want.

Another crucial thing you need to note is that the furnace will also suffer from too much use and also experience premature damage.

If the wall furnace is too large, you may expect significant temperature swings throughout the day and reduced energy efficiency owing to frequent cycling of the unit.

The frequent starting and stopping could damage your system over time. Also, you shouldn’t forget about the extra upfront cost of buying a larger wall furnace than you need.

How to Determine the Size of Rinnai Direct Vent Heater

Some of the things you will need to determine the size of the Rinnai direct vent heater include:

  • Calculator
  • Tape measure

Rinnai heaters are produced by the Rinnai Corporation of Japan and come in various sizes to suit heating demands, big and small.

Rinnai makes heaters that either use electricity or natural gas. They measure the heat output in British Thermal Units.

The size of a room is what determines whether a Rinnai heater can heat it.

First, you need to calculate the area of rooms you need to heat by multiplying the length by the width of each room in feet. After that, add the total.

You also need to determine the number of BTU per square foot that you need depending on your local climate. You can consult a heating guide such as some of the ones you can find online.

Multiply the square footage by the BTU per square foot to arrive at the total BTU rating you will need from your Rinnai heater.

It’s important to note that all Rinnai heaters are rated for a specific number of BTU. This usually ranges from 8,000 up to 40,000 and above. Therefore, this gives you a lot of flexibility about the type of model you can buy.

Different Rinnai Direct Vent Heater for Different Space Sizes

Here are some ideal Rinnai direct vent heaters to consider.

Rinnai Direct Vent Heater/EX11CTP/Propane/11k BTU

If you’re looking for an excellent indoor heater, then this is an excellent option to consider. This direct vent furnace has stainless steel bunsen burners, a warm air outlet with forced combustion, and convection through bottom front louvers. 

It also comes with an enameled tray humidifier. This heater also comes with smart features such as an electronic spark ignition, a seven-stage modulating gas valve, timer settings, and a variable speed inducer motor with a pressure switch.

It’s also an energy-efficient furnace with an electronic thermostat with a range of 600F to 8000F. This heater also comes with safe settings such as child lock and self-diagnostic electronics that continually monitor functions. 

They also provide auto shutdown codes and restart automatically when the ignition of combustion fails. It’s a gas furnace ideal for homes, condominiums, apartments, as well as commercial settings. The heater is also modular/home-approved.


  • This heater features a compact design and works great.
  • It comes with stainless steel Bunsen burners
  • Energy-efficient and also includes an electronic spark ignition.
  • Includes safe settings such as child lock and self-diagnostic electronics


  • It requires more protective packaging
  • Some buyers have reported the heater came with a ding on the side

Rinnai EX22CTWP Space Heater 

This indoor heater offers the best comfort for your home, thanks to its energy efficiency and stainless-steel Bunsen burners. It also includes a warm air outlet with forced combustion and convection through bottom front louvers.

It also features an enameled tray humidifier and smart features. If you have kids or pets in your home, this heater will keep them safe, thanks to the child lock safety feature and self-diagnostic electronics that continually monitor functions. 

It also provides auto-shutdown codes and restarts automatically when the ignition or combustion fails. 


  • Quiet and keeps your room comfortable
  • Also comes with stainless steel Bunsen burners and a warm air outlet
  • Includes smart features 
  • An energy-efficient furnace that comes with an electronic spark ignition
  • Secure settings such as child lock


  • Durability is questionable
  • It may encounter issues after long use

Rinnai EX17CTP Space Heater Wall Furnace

The third Rinnai direct vent heater to consider is this one. It is quite easy to install and very energy efficient. This heater also comes with stainless steel Bunsen burners and a warm air outlet with forced combustion.

When it comes to design, this heater can really work well in medium spaces or even your home. It also has an enameled tray humidifier, which works perfectly to offer a comfortable environment. 

Additionally, this heater comes with safe settings as it features child lock and self-diagnostic electronics that continually monitor functions.


  • The heater is relatively easy to install and energy-efficient
  • It comes with stainless steel Bunsen burners and a warm air outlet with forced combustion.
  • Includes convection bottom front louvers
  • Enameled tray humidifier
  • Safe settings – It features child lock and self-diagnostic electronics that continually monitor functions.


  • Some customers have reported horrible shipping of the product
  • You may encounter issues after using this heater for a while

What Factors Can Impact Your Heating Needs?

Several factors can impact your heating needs. This is what we’ll discuss in this section. Check them out below.

Climate & Weather

Different climates require different amounts of energy. For example, places closer to the south – Zone 1 or 2 – require about 30-40 BTU per square foot.

The middle part of the country – Zone 3 and 4 – require between 40-45 BTU per square foot, while the northern areas of Zone 5 need up to 60 BTUs per square foot.

The colder the weather outside, the more energy you need to keep your house warm. Once you have your climate zone, then you can find out about BTUs. This is a number for how many BTUs you need in your home.

You can calculate that if your home is 2,500 sq. ft., you need at least 100,000 BTU of heat to keep it warm enough.

Average Square Foot and Cubic Foot

The amount of space you have is another factor to consider when determining your energy requirements. Space – both in terms of square feet and cubic feet – plays a role.

Naturally, the larger the room, the more it demands – but don’t fall for the belief that bigger is better.

Overheating a heater or air conditioner poses several issues, including strain on compressors that cycle on and off frequently, excessive noise, and overall decreased efficiency.

A 1,000 square-foot workspace with an 8-foot ceiling height uses up 8,000 cubic feet of space when heated.

The difference between the desired and actual temperatures is 40°F if the outside temperature is 30°F, and you’d want the garage to be 70°F.

To maintain a comfortable working environment, you’ll need approximately 42,500 BTUs per hour. In addition, you should keep the relative humidity of your workplace at a relatively low level to ensure that the heat does not build up too quickly.

Propane is a clean and energy-efficient fuel that has more than twice the energy of natural gas. It’s an obvious choice for heating systems across the board.

The amount of gas burned is also dependent on the fuel type. For example, a 100,000 BTU natural gas furnace consumes about 97 cubic feet of gas every hour, whereas a similar-sized propane heater uses 40 cubic feet per hour.

The higher the efficiency rating on your heater or air conditioner, the greater the percentage of the energy consumed is directed to your heating and cooling requirements.

The Building Material and Quality

Material quality and type, as well as the age of the structure, affect this calculation.

The calculation will be altered by any additional windows that allow more light or cold air into the home and the use of insulation throughout. 

Older homes with drafty or poorly insulated walls will need the greater heating capacity to keep them comfortable.

Air conditioners in houses with many south-facing windows must be able to cool air heated by the sun.

Installers should measure the entire house, considering the layout of rooms, windows, potential shade, insulation, and climate data to determine the appropriately sized heating or cooling system.

How to Install Rinnai Direct Vent Heater

Tools Needed

  • 2 pipe wrenches
  • Adjustable pliers
  • 2 screwdrivers
  • Wire cutters
  • Gloves
  • Level
  • Safety glasses

Other Tools that You Might Need

  • Saw
  • Hammer drill with concrete bits
  • Torch set
  • Core drill with diamond head
  • Steel pipe cutter
  • Threading machine with heads and oiler
  • Copper tubing cutter

Materials You Need

  • Approved venting
  • Teflon tape or pipe compound
  • Soap or gas leak detector solution

Mounting the Wall Heater

Here are some of the steps you need to follow:

  1. First, you need to mark the mounting locations on the wall. 
  2. Disassemble the wall heater
  3. Assemble the vent pipe to the heater vent collar. Ensure you use the right gaskets or duct sealant as directed by the manufacturer’s installation instructions.
  4. Securely mount the wall heater to the wall with the proper fasteners such that the vent pipe extends through the outside of the wall.
  5. Connect the gas line to the wall heater gas valve with hard piping or an approved gas flex connector.

How to Install the Vent Termination Fitting

  1. On the outside of the house, slide the vent termination fitting right over the end of the vent pipe assembly.
  2. Fasten the vent termination flange to the siding using the appropriate plated or galvanized fasteners.
  3. Caulk the seam where the vent termination flange meets the outside wall.


The most important thing is to get advice from professionals. You should talk with a contractor, HVAC technician, or another experienced person about what you need before making any decisions. 

A wrong-sized Rinnai direct vent heater can result in poor heating performance, high energy usage, and potential safety issues if it malfunctions.