I am working on a renovation project of an 1890’s residence – project has a tight budget but high energy efficiency and green remodeling goals.

Amazing clever runs of existing ductworks in pocket door walls and chases original to house – quite impressive how well executed and thought out the original forced-air ductwork design was. During demo we discovered original ducts are odd shaped oval metal ducts WITH beautifully welded joints at set intervals (say approx. 2′). While the ductwork is smaller than what modern Mechanical Engineers would size – I find that that the craftsmanship of these ducts is amazing and am having a hard time being convinced that NOT RE-USING these would be the way to go. Mechanical Sub-Contractor talks about removing them at every meeting – I have been guarding these babies!

Anyone have an opinion:
RE-USING historic welded ducts:
PRO:
1. Re-using material – landfill benefit
2. Re-using material – cost savings in ductwork and labor – money saved seems like would better put towards higher efficiency system (currently looking at high efficiency dual fuel system .. heat-pump with Viessmann boiler (water and back-up to heatpump on extreme days).
3. Seems to me that these older ducts would have less air loss/leakage
4. I have YET to see this beautiful craftsmanship from installers these days – one has to think that something made this well SHOULD continue to provide years of service.

CON:
1. Mechanical Engineer wants larger ducts per volume calculated required for air distribution in rooms THUS would reduce volume and possible velocity noise.
2. Old – probably need to be cleaned – healthier?
3. Original ducts not insulated – would be hard to insulate where not exposed BUT this would probably be about less than 1/8 of entire ideal insulated ductwork scope.