How To Get Ductwork Through Floor Joists

Running ductwork through floor joists is a common challenge during HVAC installations.

While it is possible to achieve this, some specific rules and guidelines must be followed to ensure structural integrity and safety.

Ductwork undergoing construction

Although it might seem like a convenient solution, there are reasons why running ductwork through floor joists might not be the best option.

In this article, we'll delve into the considerations, rules, and steps involved in getting ductwork through floor joists.

Can You Run Ductwork Through Floor Joists?

Hint: Yes, But It's Not Advisable And Not The Best Option!

While it's possible to run ductwork through floor joists, it's not the most efficient way to install ducts.

When you run ductwork through floor joists, you have to cut holes in them, which weakens their structural integrity, leading to sagging floors.

Additionally, running ductwork through floor joists can make it more challenging to insulate your ducts.

If your ducts are not properly insulated, they can lose heat or cool air, which reduces the efficiency of your HVAC system and increases your energy bills.

There are better options for installing ductwork in your home.

For example, you can install ductwork in your attic or crawlspace, which won't interfere with your floor joists.

Alternatively, you can install ductless mini-split systems, which don't require ductwork at all.

Rules To Follow When Getting Ductwork Through Joists

Well, if you're still pushing it, please be sure to adhere to the following rules when maneuvering ductwork through floor joists.

These guidelines are designed to ensure that the process is executed correctly and without compromising the structural integrity of your home.

Here are the key rules to follow:

Know The Maximum Diameter

Before drilling any holes, you need to know the maximum diameter of the holes you can drill.

The maximum hole diameter should not exceed one-third of the joist's depth.

For instance, if we take the example of a 2×12 joist (with an actual size of 1-1/2 x 11-1/4 inches), the maximum allowable hole size would be 3-3/4 inches.

The measurement above is established to prevent compromising the structural integrity of the joist and to maintain its load-bearing capacity.

Therefore, it's essential always to ensure that any holes drilled adhere to this rule.

Distance Between Consecutive Holes

When drilling holes for ductwork, you need to ensure that the distance between consecutive holes is at least twice the diameter of the larger hole.

Doing so will help avoid any weakening of the joist due to too many holes being drilled too close together.

Distance From Hole To Edge

Another important consideration is the distance from the hole to the edge of the joist.

The minimum distance from the edge of the hole to the edge of the joist should be at least 2 inches. This will help to prevent any splitting or cracking of the joist.

Guidelines For Notches

If you need to make notches in the joist to accommodate the ductwork, there are specific guidelines you should follow.

The maximum notch depth should not exceed one-sixth of the joist's depth.

Additionally, the notch should not be located in the middle third of the span of the joist.

Arranging Pipes In A Stack

The golden rule here is no stacking – avoid putting two pipes on top of each other.

Stacking them like that could create extra stress points that we definitely want to avoid.

Instead, the smart move is to place the pipes horizontally next to each other.

Doing so allows even distribution of the load, reducing the risk of any trouble spots cropping up.

How To Get Ductwork Through Floor Joists

Despite previous warnings, it appears you're proceeding with installing ductwork through your floor joists.

Again, this is a complex task that requires a careful approach. Here are some guidelines to assist you in navigating this process effectively.

Consider Going Around, Under, Or Use Existing Holes

Before drilling, consider if you can go around the joist, under it, or use an existing hole.

Going around or under the joist can be a simpler solution, but it may not always be possible.

If there is an existing hole, you may be able to use it to run the ductwork through.

Also read: Can You Tap Into Existing Ductwork For Basement Heat?

If Not, Pick The Right Spot To Drill

If you can't go around, under, or use an existing hole, you'll need to drill a new one. It's important to pick the right spot to drill.

You want to avoid drilling too close to the edge of the joist, as this can weaken it. Look for the center of the joist and drill there.

Check If There’s Something On The Other Side

Check if something is on the other side of the joist.

You don't want to drill into a water pipe or electrical wire accidentally. 

If you can see an obstruction on the other side of the joist, consider its size. If it's small, you may be able to drill through it.

You may need to drill at an angle to avoid it if it's large.

If you can't see an obstruction, use a stud finder to locate the center of the joist. Adjust your drilling location accordingly.

Double Check Your Measurements

Before you drill, measure twice (or even thrice).

Confirm the size of your ductwork and ensure that your hole will align perfectly with where you need the ductwork to go.

Doing so can save you a lot of heartache down the line.

Don’t Cut It Too Big

When drilling, don't cut the hole too big. You want it to be just big enough to fit the ductwork through. A hole that's too big can weaken the joist.

Drill On An Angle, Not A Total Vertical Gap

Instead of drilling straight down, consider drilling at a slight angle. This can help efficiently route your ductwork and preserve your joists' strength.

Just ensure the angle doesn't cause problems with the ductwork’s function or integrity.

You might also like: How To Extend Ductwork To Drop Ceiling

If You're Not Confident, Don’t Try!

When installing ductwork through floor joists, precision and expertise are key.

Without proper knowledge, it's easy to make mistakes that could damage your home and impair airflow.

It can also lead to inefficient heating or cooling, increasing energy bills, and compromising indoor air quality.

Proper sealing of the ductwork is also paramount to prevent any air leaks.

If you're unsure about the process, it's best to err on the side of caution and enlist the services of a professional HVAC contractor.

They can evaluate your home's needs and ensure the ductwork is correctly installed.

Is It Safe To Get Ductwork Through Floor Joists?

When done correctly, running ductwork through floor joists can be safe and effective.

However, it requires careful planning, adherence to guidelines, and accurate execution to avoid compromising the structural integrity of the joists.

Related article: Condensation On Ductwork Between Floors – What To Do?

Wrapping Up

Running ductwork through floor joists is definitely within the realm of possibility, but it's a task that demands careful attention and a solid grasp of the guidelines.

Your top priorities should be the safety and long-term stability of your home's structure.

Remember, if you're not confident or experienced in this area, seeking the advice of professionals is a smart move.

Their expertise can give you peace of mind by knowing the job is done right.

So, has this article provided you with the insights you were seeking?

If you're now better equipped to navigate the challenges of running ductwork through floor joists, we're glad to have been of help.

Your home's comfort and safety are worth every careful consideration.

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Many thanks to OpenAI's ChatGPT for helping fine-tune the creation of this article.