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Venting high ceiling master with no returns

Jon Palmer | Posted in Mechanicals on

Hello

I’ve learned a wealth of knowledge on this site, thank you in advance.  I have an HVAC dilemma that I’d love some opinions on. 

We bought our 1st home (Westfield, NJ) at the end of 2017 and as luck would have it a 100ft oak tree fell on my house four months after moving in. We had to move out from March through September last year during repairs and our contractor also did some additional renovations.  The timing is important, I’ll come back to it. I wish I knew then what I know now!

The home is kind of two houses – a 1940’s colonial with an addition that went up in stages along the back. The whole house is about 2500 sq ft split evenly between the two. The first stage of the addition was done in the 70’s, a room off the back on a miniscule 2ft crawl with a foundation. In the early 90’s a second story was added to the addition in back, that become our master bedroom with 12 foot ceilings.

There’s only one HVAC unit in the basement of the old house. The 1940’s ductwork was designed for heat only and are undersized by modern standards. The units themselves are oversized to compensate (I know). The addition has a mix of flex duct in the crawl for the first floor and long runs of round/oval to the second floor. 

My HVAC problems are not surprisingly in the addition, which faces West. As part of the renovation, our contractor opened up the 1st floor. In doing so, he removed the only two returns that were in the addition, one on the first floor, one on the second in the master.  Every other room in the old 40’s side of the house has a single supply and return in it, both low.

Fast forward to now and it’s starting to get warm in the addition – we never lived in the house in the summer. The first floor isn’t bad because it’s open and the air mixes well. Our master is a different story. It’s a massive box with 12 foot ceilings and no return in the master bedroom, closet or bathroom. There is a ceiling fan, which helps somewhat. 

I’ve consulted with a bunch of HVAC techs.  There’s no reasonable way to run returns up to that second floor master to pull any of that hot air out or mix better. 

The solutions that everyone tries to sell me on are a second conventional furnace/AC unit in my attic, a zoned minisplits for all of the second floor bedroom (4 in total) or a single minisplit unit for the master.  It’s a high-cost of living zipcode, so the quotes are all very high.

If money weren’t an issue, I’d probably just go the zoned minisplit route but it is and I’m not sure I’d get the ROI on a 2nd system. I’d add a couple additional details, heat hasn’t been an issue and my current set-up can cool the 2nd floor down to 73 albeit running a lot. We air sealed and reinsulated the attic as part of the reno. Also, the family we bought the house from lived here for 32 years without putting a second system in.  

My question is this – would it be crazy to put ceiling returns in each of the four bedrooms (maybe two in my master) and use a multi-port ventilator fan to circulate the air back to central spot in the second floor hallway? The ventilator would be in my unconditioned attic and I’d have to insulate all the duct work.

My thinking is that this would mix the air better for the whole 2nd floor (particularly in the high ceiling master with no returns), isn’t particularly complex or costly and is a project I can tackle myself.

I’d love some other opinions!

 

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Replies

  1. Jon R | | #1

    If you are able to leave bedroom doors open, I wouldn't worry about returns at all - just increase supply as needed.

  2. Jon Palmer | | #2

    We try to but our 1yr old and 3yr old don't really allow for that as a longer term solution. Curiosity/mischievous hands, nap schedules and bedtime means a lot of the doors are closed throughout the day.

  3. Expert Member
    Dana Dorsett | | #3

    The only way to figure this out is to start with a room by room Manual-J heating & cooling load calculation, and analyzing the existing duct system per Manual-D.

    But there's promise in the statement "...heat hasn’t been an issue and my current set-up can cool the 2nd floor down to 73 albeit running a lot."

    Keeping up with the load even at the 1% outside design temperature or somewhat higher while running a high duty cycle is called "right-sized". But if "running a lot" means it's cycling the compressor on/off a lot while serving just those zones on a damper-zoned system. (Is it zoned?) It reads as if you have expectations of letting the rooms soak up heat all day with the thermostat set to 90F then be able to cool down quickly, which is the opposite of right-sizing. The ideal sized system would run more than a 75% duty cycle when outdoor temps are near the 1% design temperature.

    A ventilator fan approach is only going to create even higher room to room pressure differentials, and higher outdoor air infiltration rates, increasing your loads, and probably even reducing comfort due to the latent loads that come in with that infiltration. To get more flow, reduce the impedance of the return path.

    It sounds as if the supply ducts are adequate and it's only about return paths. Not all of the return path needs to be inside a dedicated duct. Lowering air flow resistance to a common return is usually possible using partition wall stud bays as jump ducts to provide the low static pressure paths, using the open conditioned space to move that air rather than a duct.

    Though the perception is that the old ducts are "...undersized by modern standards..." the supply ducts might actually be sized OK for a RIGHT-sized heating/cooling system running very long duty cycles to keep up with the loads at the temperature extremes but, at a somewhat lower cfm than what's there now. They may be undersized for a 3x oversized air handler and high static pressure return, yet perfectly fine (or even comfortably oversized) for a right-sized system.

    It's worth reviewing Nate Adams' videos and writings on home comfort & HVAC, keeping your house in mind:

    http://www.natethehousewhisperer.com/home-comfort-101.html

    http://www.natethehousewhisperer.com/hvac-101.html

    http://www.natethehousewhisperer.com/hvac-102.html

    It may be cheaper/better to tweak the duct system and return paths, and consider downsizing the existing HVAC system to a modulating or multi-stage solution rather than adding a second oversized system or an crazy-oversized multi-split.

    If you have the time and inclination, running static pressure measurements on your current ducts and air handler with 2-port manometer may point to other ways to optimize flow using the existing system. Taking those measurements is pretty standard fare when commissioning duct systems, but it's not clear whether that was ever done on your system, originally, or after adjustments to the duct system made during the reconstruction.

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