Strong Stack Effect in 5-Level Brownstone

singeram · October 15

Looking for Advice on Diagnosis and Solutions

Hi everyone,

I'm hoping to tap into the collective expertise of this forum to help diagnose and address a significant airflow issue in our Brooklyn brownstone with a few apartments in it.

A little background on the house:

A traditional Brooklyn brownstone with a cellar/basement and four floors above it. The house has a central staircase connecting the residential floors, with a separate staircase between the cellar and ground floor. There are doors at both the top and bottom of the cellar staircase, although neither is currently weather-stripped or particularly airtight.

We also have typical vented skylights at the roof/top-floor level.

The problem:

We experience what appears to be a fairly pronounced stack effect, with air moving strongly from the lower levels of the house toward the top. The central staircase seems to function almost like a chimney, drawing air upward through the entire house. This occurs in both winter and the summer, and all year long.

One particularly noticeable symptom is that cooking smells from the ground floor travel all the way to the uppermost floor. The upward movement of air seems substantial enough that we're concerned about how it affects comfort, temperature regulation, air quality, and overall efficiency. For example, in the winter, the top floors can get more than 77 degrees with all of the steam radiators turns off while the ground floor is 66 degrees.

What I'm trying to understand:

Root cause: How much of this is simply the natural stack effect in a tall, older townhouse, versus something that may be exacerbated by air leakage, pressure imbalances, or ventilation issues?
Cellar isolation: Would properly weather-stripping and sealing the doors at the top and bottom of the cellar staircase meaningfully reduce the upward airflow? Or would that simply shift where replacement air enters the house?
Skylights and upper-level leakage: Could the vented skylights or other roof-level openings be contributing significantly to the problem by allowing air to escape and drawing more air upward from below?
Mechanical systems: Are there HVAC or ventilation strategies that can help manage the pressure differences without creating other problems? Or is this primarily a building-envelope issue?
Diagnosis: What testing would you recommend to understand exactly what's happening? I've been looking into blower-door testing, pressure mapping between floors, smoke testing, and building-envelope assessments, but would appreciate advice on which would be most useful.
Practical solutions: For those who have worked on older multistory townhouses, what interventions have actually made a meaningful difference? I'm particularly interested in solutions that don't require major invasive construction.

We're not looking to eliminate normal air circulation between floors, and I recognize that some stack effect is inevitable in a tall building. The goal is to reduce what seems like excessive upward airflow and prevent odors and conditioned air from traveling so freely throughout the house. For instance, I recently did some work and I had to put up a plastic drop cloth to protect the floors above and below from saw dust, etc. These drop cloths filled with air like hot air balloons. Wild!

I'd also welcome recommendations for independent building-science or airflow specialists in the NYC area who have experience diagnosing these issues in older residential buildings. I am not trying to solve this alone.

Thanks in advance. I know there is a tremendous amount of practical experience in this community, and I'd really appreciate your thoughts on how best to approach the problem.

Robert O'Brien · October 15

It's air leakage at both top and bottom. Have a blower door test done to locate leaks and then seal them

Big Ed_4 · October 15

Is the vented skylite left open ?

Jamie Hall · October 15

Nothing like an open staircase going up 5 levels to act like a chimney! Very efficient… if that's what you want.

Which it isn't.

Properly weatherstripping and sealing the basement doors will help. Not all that much — it will reduce the effect by one level (yay) but that still leaves four.

ANY roof level openings or leakage are hurting you badly. That, in fact, would be the first target I would attack. You need the skylights — for a whole variety of good reasons — but they need to be carefully sealed, both inside and outside, and preferably double glazed — but be sure to leave the option to open them for cleaning. Any other roof openings, such as vent stack or what have you, should be carefully assessed and sealed. (that's your item 3).

Sort of as an extension in Item 3, any other air leaks or draughts should be found and sealed up. A blower door test may help here.

Because what you are going to want to do is reduce that natural pressure difference between floors. To that end… are there exhaust fans in the building? Bathrooms? Kitchens? Is there an opportunity for duct work — or at least one duct — between floors? One way to approach the problem — and possibly improve indoor air quality at the same time — is going to be to introduce outside ventilating air into the building through supply ducting at or near the top of the stairwell, with corresponding air removal at or near the bottom. Ideally this would be done by combining all the vents into one, and adding an exhaust vent on the ground floor — then running that through a HRV (NOT an ERV!!!) and routing the inlet air to the top of the stair well in an independent duct.

Now there is a consideration. Fire. Any ventilation system (such as I mentioned above) should — I'd be inlined to say must — have fire dampers between floors. They may even be required by code.

hot_rod · October 15

Warm air will rise, the cooler air will fall, so there will always be some movement and warmer temperatures up top.

These smoke pens are handy for finding any leaks to the outdoors. Typically used with a blower door, but with that much movement it would be an easy first step.

Even receptacles on outside walls can be a leak path.

Watch some You Tube on blower doors in use to see how they track down infiltration.

pecmsg · October 15

Posative pressure will help.

DCContrarian · October 15

There is no such thing as "natural stack effect." Stack effect is entirely caused by air leakage, in a building built to modern standards there is very little leakage and little stack effect.

Of course, that's not the building you have. Buildings of that era were hardly sealed at all.

If what you want to stop is the spread of cooking odors, you want to seal between apartments, sealing the whole building will probably make that worse.

There is a service called Aerobarrier that I've used. It's designed to seal existing construction. They pressurize a building with a large fan and then pump aerosolized caulk in a mist into the building. The mist finds leaks and clogs them. It's not super-expensive — it was about $3500 to do a 4400 square foot building — but in an occupied building you're going to have to cover and mask everything which will be a job.

I'm in Washington, DC, where they have started aggressively enforcing the energy code on new construction. I talked with the applicator and he said their main business was sealing new construction that had failed the blower door test for tightness, and sealing multi-family residences against odor transmission. They've had a big increase in demand for odor mitigation since recreational marijuana was legalized.

singeram · October 16

Thank you, all. Follow up question, I suspect a major culprit is the permanently open vents in the skylights. I have been told that this is a standard approach in old brownstones — the skylights are multiple paneled and create little domes above the roofline. Does anyone have thoughts on the historical purpose of these vents and the risks of closing them with a new type of skylight? I know the passive houses do this, but my house is anything but passive.

Jamie Hall · October 16

Think back to when your building was built. There was no air conditioning at all. There were no powered vent fans. And most — and I suspect yours? — had party walls on two sides.

And everyone wanted fresh air, or at least a sensation of it. And heating was cheap, relatively speaking.

So… what did you do? You put vents at the top of the stairs, and let natural ventilation (open windows, that sort of thing) keep your house full of nice fresh air (or what at least passed for that — in the summertime, "fresh air" in New York was a kind of joke…) and odours and so on out.

Nowadays? If — and only if — you provide powered ventilation you can and probably should seal those vents. But you still want air exchange in the house, so you will still need ventilation… somehow.

Larry Weingarten · October 16

Hi, It seems weatherstripping apartment doors that lead into the common space would be a good start. How about venting? Is it common, with vents connected together before leaving the building? I'd separate venting so you don't know what's happening in other peoples' kitchens or bathrooms. 🫣 Blower door, smoke and IR are all good tools for finding air leaks.

Yours, Larry

singeram · 2:15PM

@Jamie Hall Thank you for your input. Apologies for my lack of knowledge, I have not seen other houses with modern skylights also have air exchangers - I am no expert, but in the process of searching for this house, I did see a lot of houses and did not see air exchangers in the houses. Did you mean something else? There are only two apartments in this house and all bathrooms have vented exhaust fans and one of the kitchens has a vented exhaust hood - but they only exchange air when they are in use and not on any sort of schedule, of course. Based on all the helpful advice in this chain, I did find a person to do a blower test, but thought it might make sense to replace my vented skylights as a first step before I do that test. If anyone knows great referrals in Brooklyn, that would be appreciated.

Jamie Hall · 2:44PM

Quite right. Air exchangers tend to be rather rare — in row houses, such as yours, for two reasons. The first applies to any installation — they aren't cheap. The second, though, applies to old structure: they do require some ductwork, and finding space for ductwork can be very difficult.

The reason for considering them is combining air quality with control and energy efficiency. Indoor air quality tends to be remarkably poor, depending on both the activities of the occupants, the fact that there ARE occupants, and very often on the materials used — many modern materials off-gas not very friendly things. So you want a certain amount of air exchange with the outside air, which in most cases is of better quality. But… that air is often either much too cold for comfort, or too hot, so if you can extract some of the heat from the outgoing air and add it to the incoming air, so much the better. Which is exactly what hear recovery ventilators do. But as I say, ductwork can be a problem — you really want to have more or less even air feeding to the various spaces, and likewise you want to have reasonably even air removal from the various spaces…

On a much simpler note — yes, sealing or replacing those skylights would be a good idea.

Strong Stack Effect in 5-Level Brownstone

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