Overcoming Stack effect in 5000ft 3 floor home...

[russelms]

Hello,

How do I overcome chimney or stack effect in summer, and balance cooling in a three story fully finished house?

Background:

My house was built in 2015 and is three finished floors, with the 1st floor at roughly 2000 sqft., 2nd floor at 1600 sqft., and basement at 1400 sqft for a total heating and cooling capacity of ~5000 sqft. It has a lot of windows particular on the back of the house that is where the sun sets so major temperature loading in the evening.

We are located in Syracuse, NY (Northeast)

I did not build the house, so I didn’t have any say in the HVAC. From what I was told the house was built without a finished basement and therefore the HVAC was sized for 1st/2nd floor and then when it didn’t sell for a year the builder finished the basement including adding 7 ceiling registers and 3 returns.

The house has roughly 30 registers, and maybe 20 returns. The second floor has two rooms that have underperforming air flow due to long and bendy HVAC routes (i.e. furthest from furnace, and multiple 90 degree bends).

I typically open all the registers on all three floors in the winter to push heat everywhere, and in the summer close all the basement registers as its just a cold-sink.

The furnace is an American Standard (AUHMC100-SPEC-1D) which I’ve toggled the dip switches to push maximum CFM for heat and cool. The AC is also an American Standard (can’t find the part #) 4-ton unit. The CFM’s for heat and cool based on the table in the manual are ~1700. I change my 20x25x1 air filter monthly based on having a yellow lab, and wife being allergic to dust mites.

When I bought the house, I popped my head into the attack which was probably 30+ inches of blow in insulation as far as I could see. I have high ceilings (8.5’ basement, 9 or 10’ 1st floor, 8 or 9 2nd floor) on all floors so I couldn’t easily get into the attack to really look around.

Problems:

During the summer we have a powerful chimney/stack effect going on where all the hot air collects in our 2nd floor hallway with all the bedroom doors off it combined with less cold air flow than desired in these rooms. So roughly 10pm-2am the heat just keeps rising inside and the AC really can’t effectively cool the 2nd floor unless its permanently on all evening/night. I have the basement door closed which includes a rubber stopper along the bottom to prevent airflow running down those stairs.

The winter is less dramatic as we spend less time in the basement, but it certainly cannot contend with 1st/2nd floor temperatures and is almost always in the mid-60’s in the winter.

The finished basement is sheetrock floor to ceiling and has severely limited access to the ductwork for 75% of the basement. I have access to maybe 15 of the register cut-offs leaving many inaccessible.

Simple stuff tried in the past:

I went through and did damper leveling to try and get air flow directed upstairs in the summer, and into the basement somewhat in winter without killing performance in the bedrooms. This honestly didn’t result in any dramatic change in comfort.

I changed the furnace dip-switch settings from med too high for furnace CFM’s in both heat and cool to push as much air pressure through the system at the expensive of electricity.
Therefore, in the summer we have box fans for each bedroom upstairs blowing across the rooms from register to return, and one on the 1st to 2nd floor stairs pushing air upstairs (or I think keeping the cold air from flooding downstairs).

Possible Solutions: Where I need help

I’ve considered getting screen doors for any one of the three doors on the first floor to open in the summer with windows open upstairs to create a draft. Haven’t moved out on this because its not a year-round fix.

I had a HVAC person visit when we bought our house and he said zoning should’ve been done during the build but wasn’t and he said to retrofit it would be ~$4500 and didn’t include any of the cutouts and repairs for the basement ceiling sheetrock. He said it’s a lot of money for some added comfort but couldn’t say the results would be dramatic which made me nervous of the commitment and repair costs it would entail.

So, I am interested in what the pro’s may suggest? I am also willing to post pictures, drawings, etc. to help explain our house and HVAC circumstance.

Thanks! Mike R

[pecmsg]

3 stories
3 systems!

[kdean1]

Stack effect is overcome by sealing the basement and the attic. Attic insulation does NOT seal it.

[russelms]

Stack effect is overcome by sealing the basement and the attic. Attic insulation does NOT seal it.

I am not sure how one retrofits sealing in the attack with all of the blown in insulation, but is that a task for a HVAC person or specialized vendor? If the choice was between zoning the existing HVAC, installing a mini-split unit basement/2nd floor, or sealing which is the most cost effective?

Thanks

[kdean1]

What do you mean by cost effective?

Long term benefit comes from sealing the attic as it will reduce leaks for the life of the house.

Attic insulation needs to be removed so the top plates can be sealed to the drywall. Seal all holes in the plates which have been drilled for plumbing, wires, etc.

Short term cost effective (lowest initial cost) will be a mini-split. The house will leak as much as before.

I suspect the worst choice will be zoning unless the duct system already is divided for the house levels.

If you plan to stay in the house for 10 years or more, have a blower door test performed, assess the duct system, assess the equipment and make a plan and budget to make it right.

[Juan Madera]

If you have an open stairwell from basement to the second story, there is really no good fix other than to isolate the three floors from each other at the stairwell, that will help a lot but not cure the problem.

[pacnw]

Move.

Build a new home and have a proper HVAC plan, multiple stories = multiple systems for proper comfort.

Spend money hand over fist and probably never get what you want.