Crossover Duct

Double wide mobile homes have a large crossover duct that transfers heated or cooled air from one side to the other. It is one of those items that may be installed by the factory, the dealer or the setup crew. Improperly done it can be the source of many problems and there is lots of room to shift blame. Any time you notice the house is not heating or cooling the same on both halves there is probably a problem with the crossover duct.

The crossover duct is another one of those mystery items hidden beneath the house where poor workmanship may take a long time to appear. The duct is not supposed to rest on the ground, it should be well insulated, and it should be connected at both ends with a metal or plastic band and sealed with metalized tape. If you have not checked on yours for a couple of years it would be good to look at it. Duct tape just doesn’t hold forever and you can lose a lot of heat or cool through a leaking, poorly insulated crossover duct.

{ 27 comments… read them below }
Finton Carpenter
We are having duct work issues with our double wide. Air blows strong in master bath and in back bedroom, both on the side with the ac/ heater. Air flow is less in the center rooms on that side and almost nonexistant on side b. While I believe the crossover duct may be an issue , I do not understand how it is possible to blow great on both ends and not in the middle. Any help would be greatly appreciated.
It’s got to be obstructed somehow. What if you took the register covers off and dropped a really bright light into one of them. Then put a mirror in another. That might let you see a problem.
Good luck with it

Sheryl Campbell
We are getting water in the crossover duct. When this happens we get no air flow to the house, either one side or the other or both- no certain pattern. We have had to pierce the duct, let it drain, then close up the hole. After that the air flows fine. Until this week; no water has built up but we get sporadic air flow. It will blow somewhat OK for 6-8 hours then not well at all. We turn the unit off for several hours,then the air will flow again, but not as well as it should. The duct is laying on the ground- as far as we know it always has.
Please advise best course of action. Why is water getting in there? Is this a do it yourself kind of fix? If so where can we get a new duct in Tucson AZ.
Thank you.
A/C repair is one of my weak points since I live in New Mexico where evaporative coolers are more popular.
Your description makes me think the tube which is supposed to drain condensate from the A/C unit is plugged and the water is overflowing into the crossover duct. I would look around and see if you can find and clean it. The second part of your problem makes me wonder if the excess water and reduced flow makes the unit work harder to try and cool the house which then freezes the excess water and prevents air flow. 6-8 hours is probably about the right length of time to let things thaw out.
Let me know what you find.

there must be a duct issue, I get a/c and heat in in the kitchen, livingroom, and 2 bed rooms. I do not any thing in the den, back bedroom or the master. all of those rooms are on one side of the trailer. where do I start to look for the problem. I was told to cut open the roof by the vents to locate where the cross or pinch is. Is that correct
All the homes I worked on had the heating/cooling ducts in the floor. On doublewides there is a duct under the floor that takes the hot/cold air to the other side. I presume there is something similar with ducts in the ceiling, but have no experience with it.

Jan Hudson
I have had crossover flex duct problems many times, I bought my DW new in 94. The people that set it up laid the flex duct on the ground, I have done the same every time I have changed it (about 6X) last winter was very cold for TX, The mice came in like crazy, is there something I do or some other type of duct I can put there to help keep the mice out and the cold air in, we have had 27 plus of 3 digit temp and inside the coolest is 85. I have had the AC checked and everything is fine! Any help would be great. Thank you, Jan
What if you built a mouse proof box to hold the duct? Quarter inch plywood for most of it would keep the weight down so it wouldn’t be hard to install. You could also add extra insulation inside the box and around the duct.

How do I find the crossover pipe?
Crawl under the house and look for a large plastic tube going from one side to the other. Imagine a dryer exhaust duct only 16″ in diameter and 20 feet long.

We have an odor in one bedroom that seems to be comming from the heat duct. It has been there since our home was set up. Is there some way to find out what is going on without spending a fortune ?
You might be able to pry up the duct cover and set a mirror at an angle on the bottom. With a bright light that would let you look down the inside of the duct. If that doesn’t work you will have to open the duct at some point and see what you can find.

One side of DW gets little to no pressure and other side bliws pic iff walls, checked in all vents with light and mirrors and its clear on both, was told in a estimate that the floor needs to be dropped and another duct put in for $2,000…. i have brand new 4 ton unit and compatable with blower and working great….help
Hi Kristie,
In spite of all the nasty comments about how cheaply mobile homes are built, they ARE carefully engineered. I am certain the ductwork in your home evenly distributed the air when it left the factory. The fact you have to much volume on one side screams blocked duct somewhere. You just haven’t found it yet
Has anyone actually crawled under the home and checked out the crossover duct up close and personal?
Thats where I would start.

Remove the crappy flexduct crossover duct and install a metal crossover. Keep it off the ground, insulate it correctly and make sure the ends are securely zip tied to the openings. This should keep mice and water out, as well as very slightly help with air flow

I have double wide – four bedrooms. Problem is one bedroom stays warm at one end and the other end you freeze.
Hi Terri,
Have you always had this problem or is it a recent development?
I assume the ducts were engineered properly at the factory and the house was set up correctly. If this is a recent problem I would be wondering what changed. Is there something in the duct that is blocking some of the flow. Are the problem bedrooms on the same half of the home?
It would probably be worth having someone crawl under the home and look for problems. It might also be worth pulling up the vent covers & using a bright light and a mirror to see you can see any issues.
If all that checks out it might be worth having your furnace inspected. Could there be badly clogged filters blocking the air flow or some other problem with the furnace?
I know nothing about compressor driven air conditioning but could there be something there that is blocking the air flow or diverting it improperly.
Let me know when you figure it out. I’m curious.

can you replace the crossover duct with metal hvac pipe using 2 12″ ell’s and a pipe in the middle and insulate the outside which would take care of animals eating into the flex crossover
I don’t see why not. I have to think the only reason for the flex tube is cost. Installing a flex tube does not require any cutting, measuring, or other skills so it can be done by the lowest paid guy on the installation crew.
Steven Smith
I have a dust problem coming up through the vents. It almost looks like insulation. Would you have any way to find the problem or what is causing this?
If your duct is made like this one and the inner lining fails you could get pieces of insulation blown loose.

I moved into a double wide one side of house blows hard and cold other barely even blows at all..look under house and the crossover is not a straight shot it looks 10ft too long and is on the ground…how do i fix it i think its losing its power by the extra length…also how do u know if u have mold in ducts besides cutting them…any answers would be useful????
You should be able to cut off the extra length and re-attach it. I think some plumbers tape (metal strip) every couple of feet would hold it up off the ground.
Take the cover off of the floor ducts, hold a mirror down in the bottom of the duct and shine a bright light down the duct. You should be able to get a good idea if you h ave a problem or not. Amazon has a telescoping inspection mirror with LED lights for $12 that I think would work well.

my trailer is penned in with brick, it rains here often heavily in SC, and it floods underneath. i have ground water flooding my crossover which was lying on the ground and a mice eat thru for entry. i am replacing my crossover with 12′” pipe steel duct, available at the big box home centers for about 100.00, and spray foam the duct and junctions to seal and insulate. the spray foam is the expensive part but will pay for it self eventually in electric bills and will pertinently fix the issue. good luck everyone
That would also defeat the racoons that others have complained about.
Thanks for the tip.

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  • I just bought a new heat pump for my 12 yr old double wide mobile home. Just as before only one half of my home gets heat/air. I am alone and have family for help; What is easiest way to find and solve problem? My ductwork is foil square looking stuff. Thanks for any help.

  • Hi Martha,

    Someone is going to have to crawl under the home and take a look at the crossover duct. That would be a large tube that takes hot/cold air from one side of the home to the other. They are just insulation and plastic wrapped around wire and easily damaged by animals. Installers sometimes get sloppy about how well they fasten them and an end will come loose. Your fix may be as simple as fastening the duct back in place or you may have to replace the whole duct if it was damaged.
    Crossover duct


  • If you disconnect the crossover duct on the end closest to the furnace does the air flow feel normal?

    If yes, reconnect that end and disconnect the other end. Does the airflow there feel as strong as it did at the other end?

    If no, there is some internal problem with the duct.

    IF the duct is OK you will have to start looking for a blockage in the floor ducts. A bright light and a mirror will let you look inside the floor ducts.

    Good luck.


  • i have a double wide mobile home i get a lot of heat on one side the other side has a little heat but weak i put in a new cross over it does the same thing . and when i took the old cross over aff it gad a lot of water in it . whats is my problem ? thanks

  • Hi Robert,

    Sometimes the condensation drain for the A/C system gets plugged and the water overflows into the ducts.


  • I have an issue where somehow my toilet overflowed and ran for over an hour. The water went right into the floor vent – a lot of water. I drilled a hole and drained it, but now half of the house blows hot air and the other half is cold. (It’s winter and I’m running the heat) Is this a crossover issue? Why is the one half still moving air, but it’s ice cold?

  • Hi Andrew,

    Looking at the crossowver duct under the home seems like a good idea. The duct is just plastic and insulation wrapped around some spring steel wire so it is pretty easy to imagine the weight of water tearing it open and/or saturating the insulation.


  • I have a flex duct that needs repair, has anyone replaced the flex duct with a metal duct or installed a reducer wrapped with the insulation?

  • Hey Paul I just bought a used double wide. Is there any way to tell where to hook up your cross over duct

  • Hi Jared,
    I connects the duct work on the two halves of home. It will be easy to see when you get under there. I would start looking under the furnace.


  • We just moved in a 16×80 unit and one half of the unit blows a good amount of air as to the other half it’s almost non existent. We closed the vents in the half that blows a good amount from the ducts to see if it would help. It did somewhat but it didn’t fix the issue of half being freezing and the other half being warm what could be the cause we were told to get a window unit for the half not cooling properly which I believe is unnecessary

  • Hi Abby,
    Try lifting up the vent covers and using a mirror and a bright light to look inside the ducts. I’m thinking a leak or blockage.