Everything You Need to Know Before Building a Furnace Room

Allie Ogletree
Written by Allie Ogletree
Updated September 28, 2021
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Building a furnace room requires a professional who is familiar with the local and federal codes for the installation

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One of the best ways to keep warm and comfortable in cold weather is with a furnace, but having a forced-air furnace in an open basement space where you and your family gather can diminish the comfy atmosphere. 

Unlike a boiler in a boiler room, which requires a water heater, a furnace room uses combustion air to heat your home while keeping unsightly furnaces out of sight. Here’s what you should be aware of before building a furnace room.

4 Building Code Requirements for Furnace Rooms

There’s no one set guideline for building codes. In fact, each local municipality is different and may have hundreds of pages of codes for trained general contractors to follow. 

To avoid common construction code violations, do not DIY a furnace room installation project. However, knowledge is power, and it can still be helpful to know what coding requirements to look for when you do hire a contractor near you

Here are four main areas for coding that are worth noting:

1. Furnace Room Clearance Requirements

It’s crucial to establish adequate space within an enclosed area when building a furnace room. If the walls are too close to the furnace, the room can become dangerously hot and prevent maintenance workers from easily accessing the area.

Each county or municipality establishes space requirements and safety regulations for furnace rooms. A general standard is to have at least 30 inches of space between the walls and a furnace’s sides. 

When you hire a professional HVAC contractor near you, a pro will design the space according to your local area’s codes and ensure that the room maximizes your furnace’s performance and efficiency.

2. Furnace Room Ventilation

Your furnace room also must include an effective ventilation system to circulate air, prevent fire hazards, and protect your family. Your contractor should install an intake vent to facilitate air combustion and an exhaust vent to expel carbon monoxide and other harmful chemicals. 

Most furnace rooms should have one vent about 12 square inches from the floor and one about 12 square inches from the ceiling, although bigger and more powerful furnaces often require larger vents. Generally speaking, there should be one square inch of ventilation space per 1,000 British thermal units per hour of input (Btu/h).

Your HVAC professional can determine the correct vent sizes and install an appropriate ventilation system.

3. Ceiling and Wall Requirements

Unlike the requirements for boilers, your furnace room should never be fully enclosed without proper ventilation. Enclosed spaces increase your risk of exposure to flue gas, which includes toxins like carbon monoxide. Your furnace needs combustion air that comes in through the ventilation systems for a safe and effective burn.

4. Furnace System Energy Requirements

Your furnace also needs an efficiency rating that meets the minimum requirement stated by federal law. According to Energy Efficiency and Renewable Energy, this minimum requirement depends on location, type of furnace, and the input of the furnace. 

For the average gas-fired, warm-air furnace, the minimum requirement for an efficiency rating is 80%. For larger furnaces of this type, efficiency ratings are 95% in the North and 90% in the South. Oil-fired, warm-air furnaces have a minimum requirement of 81% for smaller appliances and 85% for larger ones.

The Process for Building a Furnace Room

The build begins with drawing lines on the floor to mark the optimal placement of each wall, followed by installing sill plates on the lines. Then, your pro might use 2-by-4-foot lumber to build wall frames, place the frames onto the plates, and install drywall on the frames to form the furnace room walls.

Additionally, the furnace installation pro should install a doorway with enough space to conveniently remove the furnace when it’s time to replace it.

Finding a Professional

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Check reviews and recommendations for a qualified pro in your area, and get at least three estimates for what the project will cost and how long it will take. You can also ask family, friends, and neighbors if they can recommend pros they’ve used in the past. Then, go with the professional that you feel will do the best job for you.

Final Furnace Room Costs

Lastly, before you get started building a furnace room, you’ll want to factor in all costs to determine your total budget. Including material and labor, a professionally built furnace room typically ranges from about $1,000 to $3,000.

Furnace Room Cost Factors

The cost of hiring a professional to help you design and build a furnace room depends on these main factors:

  • The contractor you hire

  • The material required for the project

  • The size of your room

An HVAC professional typically charges about $50 to $80 per hour along with a standard minimum fee that usually equates to about 2 hours of work. The pro will either build the room or recommend a carpenter who can. If you do end up needing a carpenter, a carpentry professional usually charges around $30 to $50 per hour and a minimum fee.

Regardless of which professional does the work, don’t forget to factor in the material costs for your furnace system. The cost of a new furnace unit alone falls between $2,600 to $6,400, with the average furnace costing approximately $5,500.

The Bottom Line

Understanding the dos and don’ts of building codes for installing a furnace room is a complex and ambiguous undertaking for the average homeowner. That’s why it’s essential that you work with a professional to safely and correctly install your furnace room.

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