[Greenbuilding] Recirculating Range Hoods & CO

[Stuart Fix]

Hi All,

A recirculating range hood generally has a charcoal filter that the air is
run through. It is designed to take out odor & grease from the air. Note
that you can't expect a range hood to stop all grease from splattering on
your stove, it's about controlling the spread of particulate matter
suspended in the air from the rest of the house.

When you're using a recirculating fan, you generally would be required by
code to have an additional exhaust fan near the stove that takes air
outside. Code is location dependent of course. The recirculation fan will
do little/nothing to help you control humidity, gaseous pollution (CO,
CO2, etc); it's simply for airborne particulates.

Generally there are two design approaches with ventilation in a
residential kitchen:

1) Cheapest & most typical:
	- Direct exhaust fan range hood. When you cook, you directly
exhaust all/most cooking contaminants directly outside. That includes
grease in the air, odors, humidity, CO, CO2, etc.
	- This approach is effective at removing particulates, but it is
extremely wasteful of energy in cold climates. You're dumping warm, humid
air directly outside.
	- This approach also depressurizes the house, which can cause
issues with combustion appliances, if you don't have a makeup air supply.

2) Most Efficient
	- Separate particulate filtration from gaseous exhaust
	- Use a charcoal recirculation filter over the range hood that
takes care of grease in the air & odors - it's effectiveness is totally
dependent on the quality of the unit you have.
	- Coupled with the home's direct ducted Heat Recovery Ventilation
system, you place an exhaust intake in the kitchen, near to the stove to
catch gasses, but not near enough to get greasy, which 	clogs up an HRV.
This ventilation system, which meanwhile supplies fresh air to the whole
home, and exhausts from the bathrooms as well, will constantly exhaust air
from the kitchen. When you 	cook, you hit a 'boost' switch on the wall
that kicks the ventilation rate higher.
	- This approach is both effective at removing particulate,
removing gas pollutants, and conserving energy.

If you have a recirculation range hood WITHOUT an HRV exhaust intake in
the kitchen, you'd be against building code in most areas I'm aware of,
and would have to open a window to get rid of CO, CO2, excess humidity
from cooking. Hope that helps.

Cheers,

Stuart Fix, P.Eng., LEED® AP
PHI Certified Passive House Designer
MASc. Building Science
Mechanical Engineer
ReNü Building Science Inc.

#206, 506B St. Albert Trail | St. Albert, Alberta | T8N 5Z1 | C.
780.554.8192 | sfix at renubuildings.com