Poorly designed Ductwork, please help!!!

[Czcrd]

Hello everyone and thank you for a wonderful website, it has been tons of help already.
Long story short, almost 3 years ago bought a Doublewide mobile home on a good property. The AC worked much better than the house we rented, but crawling under the house several times, I checked over the ductwork and realized that the design was in my opinion awful.

I have attached some pictures to illustrate, hopefully they make it easier to understand. Please not they are not to scale, just something I slapped together in 20 minutes. House 101 is the current design and Proposal 101 is well my proposed solution.

The AC (PACKAGED UNIT) has two return flex-ducts (not sure of the thickness) and two flex-ducts feed lines each running to one trunk line. One is fairly short feeding one trunk (this one has a very good cooling) and the other feed comes right under the furnace, which I think is absolutely pointless since the airflow is going to the front of the house exits under the furnace and is then being pushed through to the back.(this is the one that has worse cooling capability)

In my proposal 101 I would re-route the duct to the middle of the trunk further away from the AC unit ;therefore, evening up the flow in that trunk. And possibly adding a Y-split and using 2 feeder ducts per trunk (OPINIONS PLEASE).

Where the real horror comes in is heating... Gas furnace works well, but... The trunk that is directly under the furnace gets great heat in all the vents, but the other side of the house gets absolutely none, since the split in the duct from the furnace to the trunk further away from the furnace (which serves as an AC feed duct during cooling) has a crooked Y bent , so the HEAT blows straight through the Y from top to bottom since air naturally will not curve without resistance (plus the bend is more than 90 degrees), so instead of feeding the other trunk the heat gets blown backwards through the AC Evap coil (Recently cleaned!!!) and continues through to the return vents. I can actually feel WARM AIR COMING FROM MY RETURN DUCTS!!! Kinda like a warm air AC back-flush! (Please do not hesitate to ask questions since this is probably somewhat confusing)

I was thinking of eliminating the mess from the furnace and just run a shorter duct directly to the end to the second trunk which would also serve as a crossover duct for AIR CONDITIONING and adding a second crossover duct at the far left of the house to balance the cooling and heating properly throughout the house since the top left room gets the best AC, but no heat and the bottom left room gets the best heat, but although still OK, less AC flow.

I also though about possibly adding a 3rd Return Duct for the AC since it seems to draw lots of air through the other 2, I will post a picture of that later.

I am open to any and all suggestions, since I do not have much experience in DUCT-WORK efficiency and such. Also any tips for increasing the cooling and decreasing my electric bill would be much appreciated.

IF you have any questions about the drawings, just let me know.
I do thank you for taking time and assistance.

Victor

[Robert]

Hi,

I believe the best solution is to locate a reputable hvac tech who is experienced in ductwork and manufactured housing and allow him/her to resolve this or consult on it.


Most often when a homeowner tackles a duct job and tries to change a manufactured home duct system while keeping the trunk lines, it ends in disaster.


Most often you will/should have 1 to 2 returns (one is normal) going to the package unit.

Then one supply duct to the closest trunk.

A crossover duct between the two trunks at 1/3 or 1/2 point. Sometimes will have 2 crossovers.


There should be a damper under the furnace and also inside the supply connector at the trunk.


The dampers prevent cold air from entering furnace and warm air from escaping out to the package a/c unit.


Thanks,
Robert

[Czcrd]

Hello Robert and thank you for the prompt answer.
I looked around and found that there is a damper under the furnace (one way door allowing air to only come out of the furnace?), but I highly doubt that there is one in the ac supply line. However there are no crossover ducts anywhere.

From what you said I drew up another picture with the design you suggested is common. I vaguely remember an AC tech few years ago saying that there should be 3 crossover ducts on a mobile home here in Florida, but I am no 100% sure on this.

The purple line labeled AC supply line is also used for the crossover ducts.

My fear is that the AC only having one supply duct to the closer trunk would hamper the cooling to the further side of the house since I do believe that the AC puts out good pressure. Please do correct me if I am wrong.

Also what size should the AC supply line be??? 10", 12", 14" wide??? 14" wide flex duct is the most I can obtain from Home Depot or Lowes. Also what size should the crossover ducts be? I am not 100% sure on the width of my trunk line so this could be a factor also.

How about adding some floor registers? Would this be something to help more thorough cooling and heating of the house?

Again I do thank you for all your help.

Victor

[Robert]

Hi Victor,

Most often 1 crossover will suffice, 2 at the most. With the proper sized blower motor for the unit and system plus proper sized return and supply ducts, all should be fine.

I prefer to install hard metal ducts for crossover(s) and return and supply ducts. Wrapped with vapor barrier insulation.

Less chance for rodents damaging, less kinking, collapsing, etc.. .


The unit and home size, etc. will dictate amount of airflow needed and thus the size of return and supply piping.


That's where the services of an hvac tech would help here.

Manufactured Housing is a hit and miss task for ducts and can only be totally overcome by installing all new conventional home duct system.


Thanks,
Robert