Fixing an Insufficient Ducting System
Ductwork redesign
In 2014, our house was renovated (we bought in 2021). There are two systems, three zones. The system for the top floor is located in the attic, which is not ideal. The system is a conventional heat pump. Three bedrooms are heated adequately, the fourth gets very little heat. The ductwork for the three bedrooms that get good heat is rigid, covered in insulation. The ductwork for the fourth bedroom is flexible and runs right next to the rigid. The flexible and rigid separate at the air handler, even though the air handler and the fourth bedroom are located on opposite sides of the house.
If you are wondering, the same HVAC company installed an ERV wrong. I have asked about correcting their mistakes in other posts.
I have asked a half-dozen HVAC companies about fixing the ductwork. None will return my calls. The same companies will happily send someone out to service the heat pump or air handler, but no one is willing to re-think distribution, even though I tell them I am willing to tear the whole thing out and start from scratch.
Unfortunately, I think that means I will have to do this myself since I can’t find anyone willing to take my money.
So I have several questions:
1. Can I remove the flexible ductwork and connect the fourth bedroom to the rigid? How big a duct do I need?
2. Should I remove both rigid and flexible and upside? If so, how big?
3. If I need to increase airflow to the farthest bedroom from the air handler, can I use filters at the registers instead of a damper?
4. The fourth bedroom has two registers and a third in the en-suite. Are too many registers dissipating the heat?
Any other thoughts?
Since the ductwork was rubbish, I have delayed all the other projects in the attic. Once we have heat in every bedroom, I plan to air seal and insulate. I will ask again when that’s closer, but insulating the air handler might be part of that project.
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Replies
Have you considered adding a small mini split system to the cold bedroom?
Generally flexible ductwork is rubbish and designing fabricating and installing sheet metal is not a DIY freindly project.
I think you need to keep looking and find the right contractor for your job. Hint do not make the diagnoses yourself, do not tell them how to fix the problem. Describe your concerns and let the pro make the diagnoses and the plan then you can talk about it.
Walta
I have considered a mini-split. In addition to the two conventional systems in this house, there is a dual-zone mini-split. The garage and a converted outside room each have 9k indoor unit. However, neither unit produces much heat. So far, I have not found a company willing to service an existing mini-split. The company that installed the mini-split also installed the ERV wrong and did bad ductwork, so I do not want to contact them.
Since I cannot find anyone to service the existing Mitsubishi system, I am considering installing a MRCOOL system myself. While I am replacing two indoor units, I might be able to add a third. But the wiring would be complicated because my panels are full (both main and pony). When we replaced the gas range with induction, the electrician was able to rearrange circuits, but I am not sure he can do that again. There isn’t a second car charger to disconnect.
I would much prefer to hire professionals to deal with both problems, but I am out of ideas. I have been looking since we bought the house in 2021 and no one is willing to service the mini-split or consider how to improve heat distribution. When an HVAC tech was out for another reason (blown disconnect, etc.), I have asked about the problem without any diagnosis except that fourth bedroom is too cold. I don’t try to tell them their business.
This might be a regional problem. I’m in metro DC and tradesmen of all types are hard to pin down. When we lived in Atlanta, we had no problem getting people to show. Now it’s a battle. Several different people have said they would get back to me about the ductwork or the ERV with a quote and a plan and I never hear from them.
I often read articles on Energy Vanguard and see that they can be be consulted for HVAC design for remodels. I don't now their fees but wonder if they'd be able to provide enough specific guidance. https://www.energyvanguard.com/hvac-design/
Update: I contacted a half-dozen different HVAC companies and none were interested in fixing the ductwork in my attic. The tech would tell me it was beyond his skill set, but the foreman would call. The foreman never called.
After I had lost all hope, I found a company through a neighbor who was renovated their house. After demolition began, he found out the gas company would take months to relocate the gas line, so he decided to go all-electric rather than pause construction. His renovation required lots of new ductwork.
That company was willing to quote a fix. The flex that ran to the bedroom with inadequate airflow was replaced with rigid. Although not strictly necessary, the return lines were improved also. The total length was shortened. Plus, three flex ducts that ran across the center of the attic were reduced to one. Anyone accessing the ERV or air handler had to step over three lines, not just one.
The problem is basically solved. The fourth bedroom used to be 10 to 15F colder than the other bedrooms. Now it’s 3 or 5F. The fourth bedroom has exterior walls on three sides, plus plenty of windows and an exterior door.
The same company was willing to repair a mini-split they did not install. Every other company refused. The original install was bad, so all the refrigerant leaked. With new refrigerant lines and 6lbs of refrigerant, now I get heat from both indoor cassettes.