Why Mobile Homes Flexible Ducts Are Different?

You might be aware of it or not, but you can’t just get the ‘mobile home’ version of any duct pipe in the market. 

Because mobile home ducts come up with way more restrictions and regulatory limitations when manufactured. They’re different in R-ratings, thickness(dia), insulation, and of course, cost. Unless you have a 100% idea of how and what these differences are, you might end up sacrificing your HVAC comfort in a manufactured home. 

In this article, we’ve highlighted 3 core differences between mobile home ducts and those used in regular homes. Stay tuned. 

Mobile Home Ducts Require Higher R-rating

R-rating indicates how likely your ducting is to keep your home warm in winter and cool in summer. It’s an established insulation metric, recognized by federal entities like IMC and ASHRAE

When it comes to the R-rating requirements of mobile homes/manufactured homes, it’s quite different from apartments or houses. While ducts on the attic require R-6 and buried ductwork require R-3.5, mobile home ducts require insulation of R-8

Now, why this higher R-rating requirement for mobile homes? Look at the facts behind- 

  • Mobile home flex ducts are exposed to outside air, as they’re installed right under the floor. Thus, they’re more exposed to environmental extremes. 
  • To make sure the ducting isn’t likely to leak and cause dripping water flow underneath your floor. 
  • To prevent any insects/pests from getting into the ducting. 

As mobile home ducting, R-8 ducts offer better protection and insulation. But they come for a higher price as well. Usual R-4 ducts cost about $1.25 for 1 sq. ft., where R-8 insulations cost about $3.50 for each square foot of coverage. 

Mobile Home Flex Ducts Can’t Be Thicker Than 12” 

Flex ducts for mobile homes usually aren’t thicker than 12”, where typical attic or basement ducts are available as thick as 20” of diameter. 

This can be an unlikely situation for those who maybe have a double-wide manufactured home with a 3-ton heat pump or so. Because such a system requires flex ducts thicker than 12”. But with a mobile home, you have to stick to a maximum of 12”-14” flex ducting anyway. 

And there are a couple of reasons behind that. 

The Minimum Ground Clearance Factor

As per Housing and Urban Development(HUD), there should be at least 12 inches of clearance between the ground and a manufactured home. In the state of Florida, it should be at least 18”.

Now, as the flex duct will be underneath the floor of your mobile home, it should be thicker than what it really needs to be. Otherwise, it’ll kill the whole purpose of the basic ground clearance we’ve mentioned. 

On an inspection, if you’re found with ducting that is about to touch the ground, this might lead to several complications. Plus, this will make it easy for the pests, bugs, and insects to get into your HVAC system and cause damages worth hundreds of bucks.

installing mobile home flex duct

The Compression and Kinking Factors

To make sure there is no severe compressor or kinking taking place in your mobile home flex ducts, they have to be supported or suspended. Usually, it’s done by straps, block support, etc. 

But if the diameter of the flex ducts is larger than 12”, it becomes hard to give proper support to them. Hence, compressors and kinking take place and make the entire HVAC system inefficient and sometimes dangerous. 

Fire Risk is More for Mobile Home Flex Ducts

As ductworks are located underneath the floor, a small spark of fire can burn down the entire mobile home. There are several restrictions about manufactured home flex ducts when it comes to fire safety.

We’ll talk about both of them below-

Ductwork Has to be Class 0 or 1 For Mobile Home

Usually, mobile home HVAC appliances(ducts, dampers, fittings) are recommended to be made of metal like galvanized steel, aluminum or so. But in the case of flex ducts, it’s not quite possible by default. 

Hence, the HUD regulations insist that mobile home flex ducts have to be of class 0 or class 1, and they can’t be class 2. As a matter of fact, class 2 ducts aren’t into production anymore for mobile homes. 

Anyways, let’s have a look at what are class 0 and class 1 mobile home ducting- 

Class 0 Ducting: For these ducts, as per UL 181-1998, the fire hazard classification has to be zero. The same goes for air connectors as well. 

Class 1 Ducting: Class 1 ducting can have a fire spread rating, not more than 25, as per UL 181. They can’t also have a smoke spreading rating of more than 50.  

Duct Has to Me At Least 3 ft. Away from Heat Sources

The next concern regarding fire hazards is, the ducts and the connectors have to be at least 3 feet away from the furnace bonnet or the plenum of a mobile home. 

As a matter of fact, furnace bonnet or plenum are the most likely sources to spark a fire to the ductwork. The chance is even higher in case the duct is pretty close to these heat sources. 

Hence, they need to be at least 3 feet away from the furnace bonnet or plenum. 

Installation of Home Flex Ducts Are Also Different

Unlike regular home ductworks, mobile home ducts are highly exposed to moisture problems. Especially ducts that open in the kitchen or bathroom. Being installed underneath the floor, these duct openings often can be flooded with spilled water from the tub or the sink. 

And why is such moisture bad? There are multiple reasons- 

  • Moist ducts can let molds and bacteria grow, especially in winter when the duct has hot air in it. 
  • Moist ducts can affect an air conditioner’s dehumidifying capacity. 
  • Ducts with water in it can restrict the airflow within it. 

Because of these and some other reasons, flex ducts around the wet areas of a mobile home are somewhat different. Here’s the differences- 

They Need to Be Installed Off The Floor

To keep bathroom and kitchen duct openings from water, they’re often installed off the floor. This way, they retain minimum exposure to spilled water and moisture. 

They Can’t Be Blocked By Obstacles As well

While being off the floor, mobile home kitchen and bathroom ducts also have to be away from any kind of blockage. Usually, doors, furniture, or drapes stand too close to these ducts that prevent an even distribution of heat. 

Our Recommended Flex Duct for Manufactured Homes

So far, we’ve been talking all about how mobile home flex ducts should or should not be. And now is the time we discuss some of the best flex ducts for mobile homes that check all of these boxes. 

HVAC Premium R-8 Aluminum Duct pipe

This 25’ long duct is R-8 rated and is available in a range of sizes(7”, 10”, 12”, 14”, and 16”). For best insulation and fire protection, it’s got an aluminum coat both inside and outside. Within the aluminum layers, there’s a thick fiberglass layer. As a result, the insulation rating is more than expected(R-8.3). 

Alternative: Master Flow 12 in. x 25 ft. Insulated Flexible Duct R8

QuietFlex R-8 Mobile Home Flexible Duct

Mobile Home Flexible Duct 8" R8 25' Bag | eBay

This one is a bit more expensive than the previous one, but it comes with more safety and durability as a mobile home flex duct. QuietFlex has poured in stronger protection against UV and leaned more towards HUD/FHA standards. It’s available in 3 diameters- 10”, 12” and 14”, and each of them is 25 feet in length. 

Frequently Asked Questions

How long should a manufactured home flex duct be? 

Most popularly, manufactured home flex ducts are 25’ long. If you need any shorter length, you can trim it down. And add up 2 or more if you need longer. 

What size flex duct for mobile home?

As long as the size is about diameter, the ideal size for a mobile home is 12” of flex duct. You can go for thicker ones like 14” or 16”, but your mobile home floor should be higher than usual in that case. 

What happens if mobile home ductwork is oversized?

If your mobile home duct is thicker than 12”, make sure they’re securely strapped or supported with the floor. Don’t let them touch the ground or come nearby. 

Does mobile home flex duct reduce airflow?

If there are less turns and twists than what a flex duct can handle, they are not supposed to reduce the airflow of your HVAC system. 

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