Jet overhead!

The layout of our 1st floor ventilation system is very different from that of the garden apartment, where we have an open floor plan. Here we have two fresh air supplies, one feeding the actual apartment and a second supplying the common area towards the rear.

On the 1st floor, we have four fresh air supplies to keep the fresh air moving through all the rooms. Each of the three bedrooms has one supply plus a fourth one in the foyer.

ventilation-20

The fresh air supply diffusers in the bedrooms are placed in the middle of the ceiling, more or less right above the bed.

We were in for a little of a shock the first time the ERV was running and we were in bed. It sounded like we had a jet taking off above the bed. It didn’t matter that if the ERV was running at low or high speed, the jet noise was too much white noise for us to tolerate.

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Was something wrong again with the ERV? No, I cannot pin it on the ERV this time.

The ERV was actually running quietly, which added to the question of where all that jet noise could be coming from. We didn’t have the noise issues in the garden apartment, where the fresh air supplies and returns where basically silent.

I raised the issue during one of my many phone calls with the UltimateAir tech support this winter, and was pointed in an interesting direction.

There are a few ground rules when it comes installing the duct work for the ventilation system.

  • Size your ducts correctly
  • Use rigid metal ducts and fittings wherever you can
  • Avoid excessively long duct runs
  • Keep turns and tees to a minimum

The goal is to reduce friction and loss of velocity in the duct work. The easier the air can flow through the system, the more efficiently the ERV blower motors run.

Also recommended is to use a short piece of flex duct to connect the ERV to the rest of the duct work. The flex duct prevents any vibration from the ERV from propagating all the way through the building.

It turns out that I was a little overzealous when it came to reducing loss of velocity, and that I took “short piece of flex duct” too literally.

ERV-20

I used a 12 inch piece of flex duct to bridge the six inch gap between the ERV duct collars and the rigid metal ducts. That’s good for efficient air flow – but bad for noise!

Here is the recommendation from the UltimateAir 200DX RecoupAerator manual that I should have remembered:

“Insulated flex ducts tend to reduce air noise levels but add airflow resistance, and galvanized ducts provide the least resistance to airflow, but may amplify noise.”

“When installing the [ERV] unit, allow for a three-foot section of insulated flexible duct to go from the starting collar on the unit to the rest of the ductwork (on all four collars). This will help dampen noise being transmitted from the unit into the home or business, at the source.”

Three feet of flex duct! Not 12 inches! And including a 90 degree bend in the flex duct works wonders on cutting back on the jet noise.

While I was taking the ERV apart to replace the enthalpy wheel, I crawled into the closet, cut the rigid metal ducts back, and replaced them with three-foot sections of flex duct. Because of the crammed ventilation closet, I don’t have any photos I can share. But I will use the basement ERV to demonstrate the point.

ERV-22

The jet noise disappeared – gone! If you pay attention, you can still hear some airflow, but the difference from what it was before is like day and night.

I will file this under “good intentions that nip you in the butt” – or – “too much efficiency can get noisy.”

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About Marcus de la fleur

Marcus is a Registered Landscape Architect with a horticultural degree from the School of Horticulture at the Royal Botanic Gardens, Kew, and a Masters in Landscape Architecture from the University of Sheffield, UK. He developed a landscape based sustainable pilot project at 168 Elm Ave. in 2002, and has expanded his skill set to building science. Starting in 2009, Marcus applied the newly acquired expertise to the deep energy retrofit of his 100+ year old home in Chicago.

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