I'm sharing info from a post by Linda Wigington in the Low-cost residential particle monitoring group :

The ROCIS ISSUE BRIEF: Recommendations for Ducted Range Hoods for New and Existing Homes is posted on the ROCIS website!  Here is the link http://rocis.org/kitchen-range-hoods

The most common source of indoor-generated particles in cohort homes is a result of cooking activity. This Brief addresses both new installations and how to increase the performance of an existing range hood, as well as ways to reduce cooking-related emissions. 

Please give feedback!

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Good article that gets to the point for the folks that need it most; homeowners. LBNL will soon publish capture efficiency values for range hoods, but all of us who have existing unrated hoods must learn how to use what we have in our homes already.

Rick Karg

ASHRAE 62.2 Committee



thanks for feedback. 

In the ROCIS recommendations, I included the HVI ratings for hood capture efficiency as one of the primary criteria for a "good hood".  After we published our recommendations last month, I confirmed with HVI that they plan to have the certification program in place for this new ASTM test method by the end of 2018.  I am hoping it is earlier rather than later in the year, in order to be available for the peak home building & remodeling  activity.

I don't know if LBNL will publish their test results on CE too. Check with Brett Singer, Iain Walker et al.

That's a great article and it highlights the inadequacy of most of the common kitchen exhaust systems that we use.

First, contractors need to be educated on how to properly install ventilation equipment. I have seen too many range hoods installed with 4" ducting. I have encountered OTR microwaves vented up through the cabinet, but the fan was not rotated up as well, resulting in no air movement. The same goes for bath fans and clothes dryers.

One of the supplements recommended 8" ducting. Most of the range hoods that I have installed have 6" or 7" takeoffs, which is quite adequate for  ducting equivalent lengths of <30 ft.. The style of exterior vent hood will affect flow as well.

I did not see any recommendations on height above cooktop for range hoods. The code minimum is 18", but the higher the hood, the less capture.

My present concern looking for solutions is how to provide makeup air in a tight house for other exhaust fans, such as clothes dryers and bath fans. If all are running at the same time, that can create a significant negative pressure in a fairly tight house. The new BPI standards for CAZ testing no longer measure pressure differences in the CAZ. What happens to the effectiveness of any or all or the exhaust fans when several or all of those exhaust fans are running at the same time? Could the negative pressure also affect Radon levels in the home?

I second Rick's remarks about homeowners. There is some good information there for homeowners (I certainly learned new things)!

Hi Brad:

thx. for the insights.  Maybe we should start a picture collection of bad installs (how NOT to install) !

re: stove height, it is addressed in the document (Supplement 4, Installation, p. 1, par. 1, 32 inches or less). 

In retrospect, we should probably cross reference this, or repeat it, in the Criteria supplement too, so that designers also see this info early on. BTW, I had a problem with my hood depth matching my cabinet bottom edge (my wife did not like the look of it), so early design or layout criteria are important for cabinet design too.

The laws of physics do tell us that lower is better for range hood effectiveness.  I was originally recommending 30 inches, but found that manufacturer specs varied from 24 inches to 36 inches above the stove top. The hitch is that lower hoods that come to or overhang the front stove edge might be  "head bangers", or at least get in the way of the cook (depending on the cook's height). And for island installations where the view under the hood is important to users, low hood height would often be avoided. Also, one study found that spillage outside the front edge of a low hood could actually increase the personal (breathing zone) exposure of the cook.  So after expert review, we ended up at 32 in or less, less than maximum heights recommended.  

re: make up air and  combustion safety, direct vent combustion appliances are recommended (Supplement 3, Caveats... , p. 11, par. 1).   If they are present, combustion safety testing should be conducted (Supplement 3, p. 19, par. 1). I would add that high efficiency electric appliances should be used instead if renewable energy is available to power them.  BTW, we are  working on fixing the page numbering.

Hi Brad,

            I had a problem back in 1984 with negative air pressure in my home.  My woodstove would not light as the draft coming down the chimney would blow the match out.  Obviously something was wrong but no one could suggest what it might be.  My company built insulated metal chimney especially for woodstoves so I knew there was nothing wrong with it.  I finally realized about negative pressure and although is was not powerful it was everywhere in the house and kept up by any exhaust fan, bathroom, kitchen, clothes dryer etc.  I had a good sheet metal company and designed a makeup air device.  Look up plusaire.com it is what every house needs and will solve most of the new and older house problems.  We have sold almost 6000 units and very few people realize how easy the problem is to fix.  Tony Baptist.

Plusaire is not the solution. It only works with a furnace and only when the furnace is running.  In a reasonably tight house you could have the range hood, clothes dryer and bath fan(s) running and depressurizing the house. A wood stove would then backdraft and radon levels could increase. If the house is fairly well insulated and fairly tight, a furnace would not be running that often, but those other fans could. The Plusaire depends on pressure differential between supply and return on the furnace. I see many unbalanced furnace duct systems. The Plusaire brings colder air to the return plenum, which can thermally shock the heat exchanger. I do not see where the Plusaire affirmatively maintains a neutral air pressure in the home. Lastly, for almost 6,000 units sold, there is quite a paucity of reviews on line.

Hi Brad,

           You have made the same assumptions most HVAC guys make.  That is that the Plusaire only works when a furnace fan is operating, not so.   A Plusaire fresh air hood has no damper so if the house tries to run negative, outside air is instantly drawn into the Plusaire and delivered via the supply side and then to the area that has the exhaust fan area that is creating the problem.   A Plusaire has two plenum connections.  One to the supply side and one to the return.   The return connection is 4 times the size of the supply side so owing to the imbalance created within a Plusaire, outside air is drawn into the Plusaire where it mixes with heated air from the supply side and is dumped into the return duct where it is tempered again with returning house air prior to being passed through the filter and heated by the furnace heat exchanger for delivery around the house via the ductwork..   The fresh air hood area plus the Plusaire supply side area are equal to the Plusaire return air area.   When the furnace fan is not operating the Plusaire goes into its passive mode.   Any exhaust fan in the house will generate a negative pressure in its area.   If for instance the bathroom fan it operating in the second floor bathroom, that room will run negative, but now air is free to enter the bathroom via the supply register and traced back to the Plusaire and to the outside via the fresh air hood.  As soon as the fan stops the air stops coming in.  This works for any exhaust fan and including the biggest, the clothes dryer.   It is a pity that none of the offending appliances are designed with their own dedicated air supply.  A correctly sized Plusaire will handle any and all exhaust fans.   Fireplaces may have a fresh air inlet but history has found that a flue reversal has occurred on several systems and has set fire to the structure.   My system will handle the whole house.  We manufacture five sizes and have custom built units to fit needs beyond the norm.   We have also corrected air in houses that have very large kitchen fans, the largest being 1200 cfm.  


Tony Baptist 


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