How To Install Flex Duct in Mobile

How To Install Flex Duct in Mobile/Manufactured Home?

Flex duct for an HVAC system is as important as the veins are for the human body. But unlike regular home flex ducts, installing manufactured home flex ducts is way more complicated. 

The reason is mostly, flex ducts in manufactured homes are installed under the floor. Also, they need to be protected from being a fire hazard or a comfy dwelling space for rodents and insects. Let alone the airflow efficiency and other HVAC concerns that come up with a flex duct. 

However, we’ve crafted a handy guide with a broken-down analysis of every step to install a flex duct in a mobile home. Hang tight and let’s start. 

Why Does a Manufactured Home HVAC Needs Flex Duct?

Usually, double-wide manufactured homes require 110-120 ft of ductwork and single wide ones need 60-65 ft. Among this, a good amount of duct is flex ducts. And here are the purposes of flex ducts for both of the mobile home types- 

Crossover Ducting for Double Wide Mobile Homes

Crossover Ducting for Double Wide Mobile Homes
Source: Mobilehomeliving.org

In multi-section manufactured home units, there are two trunk ducts across the length of each unit. And a flex duct is used as a crossover that connects the trunks.

Crossover Ducting for Double Wide Mobile Homes
Source: Machineryequipmentonline.com

Mostly, the metal trunk duct comes pre-built from the factory and connects to the mobile home HVAC pretty easily. But for that crossover flex duct, you need to install or replace (if damaged) it manually. 

Ducting of Single Wide Mobile Homes

Ducting of Single Wide Mobile Homes
Source: Mobilehomeliving.org

Single wide mobile homes that use packaged heat pump units, must need a flex duct to connect between the heat pump and return air grill. Sometimes, it might also be used to connect two places within the existing heating supply, based on your heating/cooling necessities.

8 Steps to Install Flex Duct in A Manufactured/Mobile Home

From here, we’d get into the steps of installing a flex duct in a mobile home. We’ve gone through as deep as we can with the instructions so that even a first-timer can install the flex ducts right away. 

Step 1: Get the Right Size Flex Duct for Mobile Home

The size of a duct for a mobile home is defined by its diameter and length. Although we have a detailed guide on mobile home duct sizing, here goes the nitty-gritty of it- 

The Right Diameter of Mobile Home Duct

When it comes to the diameter of flex ducts, there is no minimum value. But usually, people don’t go under 8”. But about the maximum diameter you are not supposed to get a duct thicker than 12”. 

And there are a couple of reasons why mobile home ducts are different this way. 

The first reason is, too thick of ducts will fail to provide the minimum ground clearance required for mobile homes. And secondly, too thick ducts will come up with too many kinks and turns, which will restrict the airflow to some extent. 

The Right Length of Mobile Home Duct

Regarding the length of a flex duct for a mobile home, there are no hard and fast rules. That’s kind of obvious because the length depends on- 

  1. Whether the mobile home is Single wide, Double wide, or triple-wide. 
  2. The distance of the heating source and another end. 
  3. The number/amount of turns and clinks you want to have. 

However, flex ducts are available in 25 feet of length. So, you may buy as many units you want and then cut it out as per your requirements. This way, length is actually not that big of a deal, as long as you get the diameter and R-rating right. 

Based on all these calculations, here are some recommended duct sizes- 

Recommended DuctDiameterLengthR-rating
Master Flow F6IFD Flex Duct14”25’R6
Master Flow 3570352 Flex Duct12”25’R8
Atco 13102406 Flexible Air Duct6”25’R8

Step 2: Cut It at the Right Place in The Right Way

At this point, you get to know how long of duct you’ll need, and cut it accordingly. 

Tools you’re going to need- 

  1. Duct Knife: Klein Tools Duct Knife & Wire Cutter Combo
  2. Snip: Malco C5R 5-Blade Pipe Crimper

Now we’re considering whether you’ve measured or already know the length of flex duct you’ll install under your manufactured home. That said, follow these steps to cut the duct properly- 

  • Measure the required length as per the inner liner, not the outer foil. 
  • Take a duct knife and cut through the perimeter of the duct, and make sure the cut is all the way through the inner liner. Keep yourself safe while operating the duct knife. 
  • Take the snip to cut the last wire remaining (from the wire coil inside). 
  • To keep the insulation intact, roll the outer foil and tuck it into the inner jacket. 

The Duct Shop has shown the process in this video- 

youtube.com/watch?v=cSgYkDhWs_8   

On a side note, while measuring the length of the required flex duct for your mobile home, keep two things in mind- 

  • It should be long enough to avoid any kind of sharp turns and kinks. This will restrict the airflow. 
  • Also, it can’t be longer than it needs to. You’ll lose the BTU (heating/cooling capacity) of your HVAC system otherwise. 

Once you got the right point to cut, 

Step 3: Join the Flex Duct to The Collar/Plenum Safely

This is where we connect the duct-end to its source. 

If you’re installing a flex duct for the first time, you need to create a hole on the plenum first and install a collar of matching size first. Afterward, you’ll connect the duct to the collar. 

We’re going to talk about both of the processes. Have a look at the required tools first-

For Cutting Hole in the PlenumFor Connecting Duct to Collar
Sheet Metal Hole Cutter
(Our Pick: Malco HC1 2-12”)
Flex Duct Connector
(Our Pick: Ideal-Air 10” Duct Collar)
Duct sealant
Zip ties
Panduit gun
Flex fix tape(UL 181 rated)
Duct Sealant(Pookie)

Part 1: Connecting Collar To A Mobile Home Furnace Plenum

If it’s a plenum, you need to create a hole first as per the size of the duct. You’ll need a sheet metal home cutter for this. Our pick is the Malco HC1 2-12”

Once you drilled the hole, add the duct collar to the hole and mount the flanges. Make sure the connection is as sealed as possible. 

See how it’s done in this video- https://youtu.be/i4wJOcW3B0U?t=18 

Part 2: Connecting Duct to a Collar

Once the collar is set, connect the duct to the collar and make it as airtight as possible. 

For that, we’ll bring out the inner liner of the duct and tuck in the insulation and outer liner. Bring it around the neck (slightly thicker ring around the collar), and tie in a zip tie all around on the inner liner. Make sure no part of the inner liner has missed out on the zip tie. 

Finally, use a Panduit gun and tighten up the zie tie. When it’s tight enough, trim the zip tie with the gun. 

Moving on, wrap the zip tie with a flex fix tape to make sure the zip tie doesn’t get out of its place. You can seal the collar-plenum joint at this point by using some industry-standard duct sealant, also known as Pookie. 

Now, unroll the outer jacket, and make sure that you’re bringing out the inner jacket with it as well. Cover the inner line with the insulation and outer jacket properly. 

Now, put another zip tie around the jacket and use a Panduit gun like before to secure its position. Finally, wrap the zip tie around with flex fix tape with as many rolls as you feel like. 

Finally, check for a secure connection all the way, and we’re done. 

We’ve got a video from The Duct Shop that demonstrates almost all of what we’ve said. Have a look-  

https://youtu.be/ZJbyZ0wM_fQ?t=14   

Step 4: Channel The Duct and Support It with Straps

Now, you need to plan out the way your duct will go. Usually, it varies on whether it’s in the return air system or supply air system. 

Once you figure this out, you need to support the duct all the way.

Here are tools you’ll need for supporting flex duct- 

  1. Duct Straps
  2. Staple gun(for poly web straps) and Sheet Metal Screws(for metal straps).
  3. Duct Saddle Strapping System/Sling Case

First thing first, it’s the strapping. When it comes to flex duct straps, there are three options available- metal strapping, plastic strapping and poly web strapping. 

For ease of use, we’d recommend poly web strapping for those of us who’re not HVAC enthusiasts. They can be used just with staplers. For a more secure and durable connection, go for metal duct hanger straps. Plastic ones aren’t recommended by most professionals. 

Here’s a head-to-head insight of both of these strapping options- 

Factor of ComparisonPoly Web StrapsMetal Hanger Straps
Made of PolypropyleneGalvanized Metal
FlexibilityMoreLess
DurabilityGoodBest
Ease of InstallationEasyModerate
Nail HolesNo (doesn’t require)Alternating holes (bolt and nail)
Our PicksDiversiTech Woven Duct Strap
With nail holes- Oatey 33923 Galvanized Hanger Strap
Without nail holes- Diversitech 710-001 Strap

When it comes to supporting the ductwork with straps, there has to be some extra effort to keep them off ground. Because, if the flex gets in touch with the ground, rodents, insects, dust, debris, and dozens of other unexpected things will find their way into the ducting, and eventually your house. 

Hence, HUD has very specific requirements about how you should suspend the ducts from the trailer floor. 

Here are the rules- 

Rule 1

Supporting straps have to be 4 feet or closer to each other. This leaves no portion of the duct unsupported which might bend and touch the ground eventually.

Rule 2 

The thickness of the supporting strap has to be at least ½” wider than the spacing between two consecutive spiral wires.

Why this is important is- the straps won’t be able to slip between the spiral metal wires. Thus, there won’t be any unexpected bend in the ductwork. And also, the chance of the duct being bent enough to touch the ground will be minimized. 

Apart from these rules, there are a few more advices to support the ductwork better- 

  • Use pads underneath the straps for better and safer support. 
  • If you go with metal straps, use sheet metal screws to secure it. 

Tip: To have a minimum friction loss, kinks and sags, consider using the Duct Saddle Strapping system available on Amazon and GEMAIRE. You can also use a Duct Saddle Sling Case like this one. These things will add up to the overall efficiency and airflow of your ductwork. 

Here’s how these things work- 

https://www.youtube.com/watch?v=CKKoY_rj5ek 

How Much Does It Cost to Install new ductwork?

For the flex duct, the average installation and purchase cost for each foot of duct is $40-55. Based on how much you need, it can vary, depending on how many collars, straps, etc. 

For single-unit ducting, it takes about 60 feet of flex duct, resulting in a cost of $2100 to $3100. 

For double unit mobile homes, you’d need 110-120 ft of flex duct, which will cost $4400 to $5000. The cost of securing the duct will be more than single unit ducts because the overall weight will be double. 

Frequently Asked Questions

How to Install New Ductwork in a Mobile Home?

In case you are installing flex ducts to your mobile home for the first time, you need to create a plenum first and add a collar to it. The rest of the procedure is as explained in the guide above. 

What Size Flex Duct for Mobile Home?

Mobile home flex ducts are about 10-12” in diameter, and 25 ft in length. If you need longer flex ducting than that, you have to joint more than one flex duct together. 

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