Any HVAC people

EdFred

EdFred

Taxi to Parking
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Feb 25, 2005
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Michigan
Display Name
The Ed
Home Airfield
9D9 / 6Y9 / 88TN
So I have a house that was rebuilt after a fire years ago. When it was rebuilt the HVAC system was redone. Basic rectangular plenum off the top of the furnace. Varying size duct pipes coming off all 4 sides of the plenum. Downstairs, pretty much each room (except 1 living room vent and 1 bedroom that share) are on their own run off the plenum. Upstairs has a 12" duct coming off one side of the plenum. That was capped as the upstairs was unfinished and I lived alone. When I was alone, I left all my doors open to every room, so the temp downstairs just balances naturally. Upstairs remained closed off. (Had an insulated half wall, laid over the stairway opening)

Then I got a wife, 2 kids, and 3 dogs. The upstairs got finished, and the 12" duct that goes out the side of the main plenum got uncapped. It goes vertical through a chase, then turns horizontal, narrows to 8" diameter, and enters a straight 8" diameter run that goes the length of the house. It has 3 T's to supply the office and en-suite area, and each end of the run finishes at the bedrooms.

Now, however, everyone has to have every door closed even if no one is in the room. One kid would complain it's too hot, other too cold. (in any and all seasons) So, we installed dampers on the the downstairs and futzed with it over a few days until everyone is happy.

Winter is fine, since warm air rises, and the upstairs is OK temp wise. I like cool, April and daughter have electric blankets that they use anytime it gets below 72. Summer however. Oof. Shut all the dampers downstairs, try to force everything up, but it's just not enough. Downstairs stays cool even with the dampers completely closed, but just can't force enough air to keep the upstairs comfortable. Is there some sort of standard plenum modification that would allow us to throw a lever and force ALL the air from the plenum into the upstairs run? The dampers still allow some air through, and just can't get enough cool air upstairs. Downstairs you can put your hand in front of the vents (when dampers are open) and feel the air coming through every single one. Upstairs, barely anything. Willing to tear the plenum out and redo it, if someone has a workable idea.
 
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Need someone to come in and run the numbers on the duct work and see if there are improvements that can be made. Sounds like there is a balance problem. 12" to 8" with several tees and a couple of 90 deg turns sounds like the flow is being choked off quite a bit.
 
Craig said:
Need someone to come in and run the numbers on the duct work and see if there are improvements that can be made. Sounds like there is a balance problem. 12" to 8" with several tees and a couple of 90 deg turns sounds like the flow is being choked off quite a bit.
Click to expand...
Yeah, I may have to crawl in the attic and replace the ducting. When the upstairs was open and I uncapped the capped duct, it would heat/cool the entire thing in a hurry.
 
You normally have much better luck adjusting the return air side than the pushing side. Often the main floor returns are closer to the unit and very large. This leads to the upstairs returns having more resistance and it doesn't turn the air over as much.

The other thing you can do that helps is buy a thermostat with a CIRC feature. This runs the fan for a certain percentage of time regardless if the thermostat is calling for temp. It helps even the house out.
 
Do you need more returns upstairs?

If the kids don’t like their temperatures, a slight fix is to leave the doors open (yes, I’ve had kids and know how well received the suggestion will be, lol).
 
The classic multi level home problem. We're 3 stories; top is always too hot. I've considered putting in a whole house fan with a duct from top to bottom and controlled by temperature differential.
 
455 Bravo Uniform said:
Do you need more returns upstairs?

If the kids don’t like their temperatures, a slight fix is to leave the doors open (yes, I’ve had kids and know how well received the suggestion will be, lol).
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It used to be both kids were downstairs and the dampers were fine with getting temps adjusted. Then [1] wanted the upstairs bedroom because [0] made too much noise when [1] was trying to sleep. (College schedule vs high school) Since that happened, and the upstairs went from only keeping one bedroom at a good temp to diffusing the airflow to two, complaints have began again. Mostly by me and the electric bill.
 
A booster in the most problematic ducts can really help, and isn't too pricey.
 
+1 for booster fans in each room, abd if you want to get fancy attach thermostats to them.
 
Unfortunately I don’t know anything about HVAC, sorry.
 
I am not in the HVAC business but know a bit from having been a landlord with four homes. I put an HVAC system in two of those, helped my father install in one, and the last home we put in two new systems.

Our primary home is a bit like yours. Home plans came from a modular company so basically we live in a doublewide downstairs, single wide upstairs. Upstairs was unfinished to start, now mostly finished. We had a classic heat pump split system (coils outside, air handler inside) and added three outlets and a return to the 2nd floor. It always stayed hot and the downstairs never felt the same. What we learned is that "best practice" is to have separate floors on separate systems. Basically, you need to deal with it as you are or just add in a 2nd system and put your duct work back the way it was.

The mini split system sounds great and makes the individual zoning easier. Ours had a four inside head maximum. In your situation I would keep the original system as long as it works, then add a mini split for the upstairs.

SPEAK UP NOW IF YOU HAVE SOLAR
Minisplits are sensitive to power fluctuations, consider a surge protector. Daikin gives us 12 yr parts and labor warranty.

I predict that doing any additional duct work will not fix the problem. Your original HVAC was sized for what you had.

While folks read this, I'll advocate for an interior humidistat, readily available. Lower humidity in summer helps keep thermostat higher in summer. We have a dehumidifier that runs after morning showers.
 
4RNB said:
I am not in the HVAC business but know a bit from having been a landlord with four homes. I put an HVAC system in two of those, helped my father install in one, and the last home we put in two new systems.

Our primary home is a bit like yours. Home plans came from a modular company so basically we live in a doublewide downstairs, single wide upstairs. Upstairs was unfinished to start, now mostly finished. We had a classic heat pump split system (coils outside, air handler inside) and added three outlets and a return to the 2nd floor. It always stayed hot and the downstairs never felt the same. What we learned is that "best practice" is to have separate floors on separate systems. Basically, you need to deal with it as you are or just add in a 2nd system and put your duct work back the way it was.

The mini split system sounds great and makes the individual zoning easier. Ours had a four inside head maximum. In your situation I would keep the original system as long as it works, then add a mini split for the upstairs.

SPEAK UP NOW IF YOU HAVE SOLAR
Minisplits are sensitive to power fluctuations, consider a surge protector. Daikin gives us 12 yr parts and labor warranty.

I predict that doing any additional duct work will not fix the problem. Your original HVAC was sized for what you had.

While folks read this, I'll advocate for an interior humidistat, readily available. Lower humidity in summer helps keep thermostat higher in summer. We have a dehumidifier that runs after morning showers.
Click to expand...
No solar. It was (re)sized for the two floors when the furnace was replaced 10ish years ago. But the HVAC company didn't do the duct work for the upstairs, just the 12" out of the plenum and capped it in the chase. had that done by a student of mine that used to own an HVAC company. Maybe I have to go resize the upstairs ducting. Going to add in some extra cold air return vents first (easiest thing to do to start).
 
On a rental house I owned way back when. Had multiple T's off a main line running across the house. The bedroom on the southern end of the house was at the end of the line, and was always the hottest in summer.
The solution the HVAC company installed was a "booster" just behind the register for the last bedroom. Just an overpriced fan that pulled air to the bedroom, think bathroom or kitchen exhaust fan. The HVAC company setup dual pole switch to power it. When the HVAC fan was on, it was on, or when the room temp exceeded 72 it turned of to force some "local" air flow.
Other change we made was fan on the furnace was always on low at a minimum to help balance the temp.

Tim
 
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