One central HVAC air return in a closed hallway, jump ducts to rest of house?
Sanity checking an HVAC design possibility…
The question: If an HVAC system has a single central air return in a short hallway that often has closed doors, is it ok to add a jump duct to pull return air from the living spaces?
The context: We’re looking to use a ducted heat pump in a new house, only 1,200 sq ft, in CZ3C. Based on a Manual J load calc using CoolCalc, with modern energy efficient construction, we will need well under 10,000 BTU in total. (I’m sure a typical HVAC installer would propose 2.5 tons 😉
Based on that, we’re considering the Mitsubishi or Fujitsu 1 ton ducted unit, which are already oversized for our needs. Whichever we choose, it will modulate and never run at max capacity. They’re quiet and efficient and people love them on GBA. We are thinking to install vertically.
To reach all the rooms, it will take a fair amount of ductwork, and there’s very limited space, based on the architectural design. All of the supply ducts will fit, no problem. Having return duct runs to maybe 3 locations might be possible, but very tight, and it also edges up the static pressure of the system. It would be much simpler to have a single central air return.
The catch is that the single air return would be in a short hallway that may often have a closed door to the main part of the house, mainly for noise reasons. (It’s not the air handler we’re worried about — the Mitsubishi and Fujitsu are very, very quiet. There’s also a heat pump water heater and laundry, and those could add up.)
It’s possible to add a vent to the bottom of the doors to get more airflow, and maybe that would be enough? It would also partly defeat the goal of reducing noise.
So here’s the question: what if we could put a jump duct with flex duct to get to the other side of that door? That kind of turns the whole hallway into a return air duct. It saves some space from connecting the return air duct to the air handler and having it do a 180 degree turn.
Any reason this wouldn’t work?
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