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Chimney Smoke Sucked Into Makeup Air Unit (MAU)
I live in a twelve unit, four story, apartment style condominium. Each unit has a wood-burning fireplace with the chimneys around the perimeter of the roof. The roof is flat. Also on the roof is a MAU which feeds ventilation air to the hallways in the building. It sits roughly in the middle of the roof.
Occasionally we have a problem where smoke from one of the fireplace chimneys gets sucked into the MAU filling the building with a smoky smell, sometimes quite heavy.
Is this a normal consequence of having fireplace chimneys and an MAU sharing the same roof, or is there something wrong with the chimneys and/or MAU design?
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6 Replies
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MarkH
Many years ago when I was on our board we had a similar problem; not wood fires, but odours from the exhaust vents from the building’s kitchen and bathroom extractor fans and sewage vent odours, as well as fumes from the old MAUs being sucked into the air intakes of the MAUs.
The solutions were (1) more powerful MAUs; although the old ones met the 1979 building code, in 2005 they were no longer acceptable. In addition, (2) the air intakes for the MAUs were raised about 3.0 m /10 ft above the rest of the rooftop, providing access to cleaner air.
Perhaps those solutions could work for you. An alternative might be to extend the chimneys to a greater height. I’m not an engineer so these are not technically appropriate suggestions; talk to a professional HVAC engineer.
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MarkH
In large developments like yours, Terry, and ours, this is an item that must be included in the Reserve Fund Study and Plan. I noticed that recently, about 15 years after the original replacements were installed after the 1979 vintage units were ‘retired’, that at least one ‘new’ unit has been replaced again. I haven’t looked into the details.
In these days of increased awareness of, and need for, energy efficiency, I wonder:
- Why wood-burning or natural gas (which is methane) fires are still permitted?
- Should those responsible for the MUAs and other ventilation systems be considering energy-recovery ventilators, where the exhaust air is used to warm (or seasonally, cool) incoming ventilation air?
When we renovated our apartment in 2012, we took out the gas fireplaces and ‘window-shaker’ air conditioner/electric heater units and modernised the perimeter hot water heating system. We removed four large holes in our apartment that did little to ‘improve’ the heating or cooling in the apartment and substantially reduced the likelihood of a freeze-up in our heating system due to windows left open. But that’s another story…
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Posted by: @MarkH-2
Many years ago when I was on our board we had a similar problem; not wood fires, but odours from the exhaust vents from the building’s kitchen and bathroom extractor fans and sewage vent odours, as well as fumes from the old MAUs, being sucked into the air intakes of the MAUs.
Are you talking about exhaust from the MAU burner being sucked into the MAU intake?
The solutions were (1) more powerful MAUs; although the old ones met the 1979 building code, in 2005 they were no longer acceptable.
So more powerful MAUs were needed simply to meet 2005 code requirements, not as a solution to the odour problem?
In addition, (2) the air intakes for the MAUs were raised about 3.0 m /10 ft above the rest of the rooftop, providing access to cleaner air.
Interesting idea. But it might look kind of strange on our building which is relatively small.
Perhaps those solutions could work for you. An alternative might be to extend the chimneys to a greater height.
Yup, that would also work, but probably raising the MAU intake would be cheaper.
The chimney tops and the MAU intake are all on about the same level. One idea I have is to lower the MAU intake to the surface of the roof. I’m thinking it might be just low enough to allow any smoke to drift past a few feet higher.
I’m not an engineer so these are not technically appropriate suggestions; talk to a professional HVAC engineer.
I’m actually a mechanical engineer, but I have very little experience with HVAC. I would like to hire an HVAC engineer to look at it (if the board agrees), but I don’t know exactly where to find one. Do you know which company was used by your building?
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Posted by: @MarkH-2
Should those responsible for the MUAs and other ventilation systems be considering energy-recovery ventilators, where the exhaust air is used to warm (or seasonally, cool) incoming ventilation air?
For replacement MAUs I think the issue is that it is cost prohibitive, or even impossible, to retrofit a heat recovery system to a building that wasn’t designed for one when it was built. I could be wrong, but that’s my impression.
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MarkH
@jonfkleingmail-com The concern that the engineers expressed was over exhaust fumes being sucked into the ‘house’ air intake. The answer expressed by the experts was to separate the intake from the burner’s exhaust. It was done – I have lived in top floor apartments in two of our three buildings where the output from the MUAs is strongest. I installed CO2 detector/alarms in our apartments, and have never been ‘alarmed’. Success?
The underlying problem we had was that the 1979 vintage MUAs did not provide sufficient hallway pressurisation to ensure smoke from an apartment fire would exit the windows rather than enter the halls, so we needed to upgrade the hallway pressurisation. Odour (cigarette smoke, cooking) was also a problem, but from apartment to apartment. When the wind was strong and windows were open, the pressure on the windward side of the building could overwhelm the MUA pressure in the hallway, so odours crossed the hall into apartments on the leeward side of the building 🙁
The taller air intakes to the MUAs do indeed look strange. One sees them building-to-building. From the ground, they are not so noticeable on our eight and ten storey buildings.
If you lower the MUA air intakes, they will be at the same height as sewer vents and exhaust fans from the bathrooms and kitchens (if they are ducted upwards, as ours are). That could be a new problem.
I think that since our work was done, the companies have changed and I do not recall the name of those who did the work around 16 years ago. I suggest you consult APEGA or the Canadian Condominium Institute – Southern Alberta chapter for professional members specialising in this type of work.
Take a look at the (now old) Green Condo Guide from the Pembina Foundation. It doesn’t mention ERVs particularly (they have improved since then). You might also find this article interesting: Largest Passive House Retrofit in Canada https://www.passivebuildings.ca/post/largest-passive-house-retrofit-in-canada
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@MarkH-2
Thanks for the info. I had been thinking it was unlikely the original design of the chimneys and MAU was incorrect, and was focussing on modifications made since construction. However, now I am starting to think that the original design may have been flawed. Your experience provides an example of flawed HVAC design at original construction (if I understand it correctly).
My building was also built in 1979. The MAU was replaced in 2007, but looking at the documentation that we have the replacement provides essentially the same air flow as the original. The air flow coming under my unit door also feels substantial when felt with a hand, and there haven’t been significant issues with odors crossing the hallways.
A potential solution was suggested to me: run inlet ducting from the MAU over the edge of the roof and down the side of the building a few meters. This would distance it from the chimneys. For our building this could very well be an option. One side of the building faces another apartment building of similar height. So the duct work would be hidden, only noticeable if looking down the gap between the buildings.
I’ll have to check the CCI web site, didn’t think about them. But I don’t think APEGA lists members by area of practice, just by name or company number.
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