Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.
If our community has helped you, please consider making a contribution to support this website. Thanks!

Old Home full remodel in Zone 5A — need advice on new ductwork design, Manual J/D, attic ducts

Options
MichaelT
MichaelT Member Posts: 39
in THE MAIN WALL

Hey everyone, I’m looking for advice before HVAC contractors come out to quote new ductwork.

We are remodeling an old historic house in Climate Zone 5A in Michigan. The house is being opened up during the remodel, so I want to make sure the HVAC/ductwork is designed correctly while access is available.

I’m doing the electrical and plumbing work myself, but I have not done ductwork before. I’m not necessarily trying to DIY the entire HVAC system, but I want to understand what a proper design should look like so I can ask the right questions and avoid bad ductwork.

House info

  • Old home, built around the 1880s
  • Full remodel
  • Climate Zone 5A
  • Main floor: about 1,250 sq ft
  • Second floor: about 1,250 sq ft
  • Sunroom: about 180 sq ft
  • Breezeway: about 180 sq ft
  • Basement: about 1,000 sq ft
  • Main floor ceiling height: about 8 ft 8 in
  • Upstairs ceiling height: about 8 ft
  • Basement ceiling height is low — approximately [insert height here]
  • We would like the sunroom and breezeway to become conditioned spaces
  • Windows are about 20 years old

Current equipment

  • Furnace is located roughly in the center of the basement
  • Current furnace: Rheem RGRK-10EZAJS, around 20 years old, still working
  • Furnace is a 90+ condensing gas furnace, approx. 105k BTU input / 92% AFUE, two-stage
  • Current AC: 4-ton Goodman GSX140481KD
  • There is a large old chimney running from the basement up through the house
  • The chimney is currently being used for the water heater venting

Basement / ductwork challenges

The basement framing makes duct routing tricky.

The joists run north to south, but because it is a very old home, the joists are notched and tied into three large beamsspaced evenly across the basement.

Because of those beams, it seems like ductwork may not be able to stay neatly inside the joist cavities. To cross the beams, ductwork may need to drop down and go around them, outside of the joist cavity, which could be an issue because the basement ceiling height is already low.

I’m trying to understand the best way to design ductwork around these beams without creating a bad system with high static pressure, poor airflow, or a low basement ceiling full of duct drops.

Upstairs duct idea

One thing I’m considering is running ductwork up to the attic and then dropping supplies down into the upstairs bedrooms from above.

I’m not sure if this is a good idea in Zone 5A, especially with attic insulation planned. I’m wondering whether attic ducts are acceptable if done correctly, or if they should be avoided unless they are inside conditioned space or buried/encapsulated properly.

Planned insulation / air sealing

  • Attic: about R-50 blown cellulose
  • Exterior walls: about R-23
  • Basement walls: likely insulated with foam board
  • Because the house will be much tighter than before, I’m also trying to understand whether we should add an HRV or ERV for fresh air.

What I’m trying to figure out

  1. Should I insist on a room-by-room Manual J before any ductwork design?
  2. Should I also ask for Manual S equipment selection and Manual D duct design?
  3. Is my current 105k BTU Rheem furnace likely oversized after the insulation work?
  4. Is the current 4-ton Goodman AC likely oversized after the insulation work?
  5. Should the ductwork be designed around the current furnace/AC, or around possible future replacement equipment?
  6. For a two-story old house, would you recommend one system or two systems?
  7. What is the best way to handle the upstairs: basement-to-second-floor ducts, attic ducts dropping down, high-velocity system, mini-splits, or something else?
  8. If using attic ducts in Zone 5A, what is the right way to do it?
  9. How should returns be handled upstairs and in bedrooms?
  10. Should every bedroom have a return, or are transfer grilles/jump ducts acceptable?
  11. What should I look for in terms of supply trunk sizing, return sizing, filter sizing, static pressure, and balancing?
  12. What are the common ductwork mistakes I should watch out for when getting quotes?
  13. For a tighter renovated house in Zone 5A, would you recommend HRV or ERV?
  14. Are there any concerns with the old chimney only venting the water heater if the furnace is already PVC vented?
  15. What questions should I ask contractors before hiring one?

My main goal is comfort and doing this right while the house is open. I don’t want loud ducts, high static pressure, weak upstairs airflow, poor return air, short cycling, poor humidity control, or an oversized system.

I’m not looking for a rule-of-thumb furnace or AC size. I’m trying to understand what a proper design should include and what numbers I should ask for before choosing a contractor.

Any advice on duct layout, upstairs strategy, Manual J/S/D, attic ducts, returns, HRV/ERV, or contractor red flags would be appreciated.

Comments

Categories