Range hood preps

We completed the tasks on our to-do lists in preparation for the insulation installation. The old basement stairs are closed up and the basement bathroom has a ceiling (and the 1st floor bathroom a floor).  We installed the DWV plumbing and DWHR unit and eliminated the thermal breaks around the 1st floor edges.

I know it is hard to believe, but I had a few quite moments in that process where I was sitting in my basement sipping coffee contemplating. That got me into trouble – sort of – because I noticed that my original to-do list was too short. There were a couple of items that I missed.

Take the kitchen range hood for example, which is a critical piece of equipment managing the indoor air quality (IAQ). Because the garden unit will be effectively air tight, we have to assure that excess moisture and cooking odors are exhausted to the outside.

This involves a wall penetration for the range hood exhaust, which I should take care of before we start with the insulation.

Equipment selection

I had researched and purchased the range hood a while back. The selection and decision making process was guided by our goal to reduce our overall energy demand.

The Energy Star program is an excellent resource when it comes to researching efficient appliances. It provides a product list of Energy Star certified products. Each product is listed with its efficiency rate. In the case of the range hood, we are talking about how many cubic feet per minute (cfm) get moved by one watt.

There are a lot of very slick looking range hoods out there. But in the end, we were most enthralled by the one that moved the most air for the least energy input. Call me cheap – I won’t deny it.

Ventilation level

Something to think about: How much air should the range hood move? That is an important and tricky question considering that the garden unit is effectively air tight.

If I exhaust air to the outside, I need some make-up air coming in— particularly if the range hood is operating at a very high rate, such as the 600 cubic feet per minute (cfm) of some downdraft models. If there is no make-up air source, the interior space gets depressurized to the point where it can cause all sorts of problems.

To get around the make-up air problem we could crack a window open. Or we could install a make-up air valve, which opens once there is negative air pressure in the living space.

Both options carry an energy penalty on cold winter and hot summer days.

Another approach is to use modest level of exhaust air flow. After digging around the GBA web site I came across recommendations for tightly built homes. The consensus that emerged was that 150 cfm is a good exhaust rate without risking excess negative pressure in the building.

It is also worthwhile noting that range hoods generate the least noise and require the least energy at lower flow rates, such as 150 cfm.

Punching the hole…

… through the wall requires me to take our brand new range hood out of the box and see where I should run the exhaust duct through the wall.

I mark the location of the duct on the wall, get the hammer drill out and start drilling along the outline. Once the drilling part is done I can remove the brick and mortar, connect the end cap and damper to the duct, place it into the opening from the outside, and foam out any gaps.

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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