Kitchen Range Hoods :: Unintended Consequences

M y offer to range hood manufacturers, dealers and sales and marketing people.

. sticking a 1200 cfm exhaust fan into a typical residential kitchen is not like playing with a hairdryer it s more like having a home appendectomy with the suction side of an industrial grade leaf blower.

. what these hood S M folks (sales and marketing) need is a simple lesson from the Whitney Houston School of Building Science; you know the Crack is Whack rule and when suck trumps blow, holes and cracks in the enclosure become the conduit to contamination.

. commercial range hoods in residential applications without proper make-up air fly s in the face of everything Health Canada wants Canadians to avoid.

Outdoor air does not equal fresh air

Only when the outdoor air is free of contaminates can it be considered fresh. It should never be assumed to be fresh when common outdoor pollutants include particulate matter (organics and non organics), ozone, moisture, polycyclic aromatic hydrocarbon (PAH's) etc.

The following industry design guides do not replace the need for a design professional - in all cases the authority having jurisdiction must be consulted and where guidance is absent consult with a design professional .

Gas ranges should have at least 100 cfm exhaust air per 10,000 Btu/hr input and a minimum of 500 cfm.

Add 200 cfm for cook tops with grills.

Never have less than 100 cfm per 12 width of cook top surface area. See Schlieren images at different exhaust rates

per linear foot.

The cfm required is the net flow after allowing for duct and fitting pressure losses, i.e. its not sufficient to buy a fan for a required cfm only to loose its capacity to duct resistance.

Mount hoods between 18 to 24 for standard units and no more than 30 for commercial models.

Install a make up air system equal in capacity to the exhaust air system.

For gas ranges provide combustion air as per the authority having jurisdiction.

Do not use recirculating vent hoods, vent all products to the outdoors.

For quieter operation use a remote fan instead of a fan located above the stove top.

For residential units select the fan using standard selection procedure accounting for duct losses at 600 fpm to 900 fpm.

Use 16 guage or 18 gauge insulated stainless steel ducting, i.e. do not use flex duct.

Pitch ducting downwards back towards the stove top.

Install an appropriate back draft damper at the exterior surface of the enclosure.

Use a hood that covers the entire stove top plus a minimum additional 6 on each side.

Reduce drafts around the range hood from ceiling fans, windows, doors or supply air outlets.

Do not blow make up air directly at the hood or stove top. Let the range hood do its job of capturing fumes and let the range hood fan do the exhausting.

Air speeds external to the range hood should not exceed 100 fpm.

Preference is given to 100% dedicated make up systems. Alternatively make up air could be delivered from supply air grills within the vicinity of the hood plus air supplied from floor registers used to condition the space.

Provide a dampered make up air duct to the return air stream of the air handler. Interlock the damper with the range hood, i.e. end switch on damper closes contacts on range hood fan.

Conditioning of make up air must account for energy and mass transfer, i.e. heat, moisture, particulate etc.

For additional support on this topic visit our visitor services page.

Why are we not surprised.

Measured airflows were substantially lower than the rates claimed in product literature for most of the fans evaluated. Only two of the 13 independent models (three installations used

same model) had actual airflows that were 90 percent or greater of the advertised values.

LBNL, 2011

Offer:

Are you a range hood manufacturer, dealer, sales and marketing person?

If you have professional design guidance for residential range hoods that can pass my sniff test I'll give you the opportunity to submit it to me for consideration.

If I like what you have to say I'll include a link from this page to your page at no cost to you.

Limit to the best three manuals.

Instructions:

Post a link to your manual in the promotional tab at our Linked-In discussion group .

Once posted, I'll have a look and if it meets my criteria I'll post the link here.

Readers. if you don't see three samples it's because we haven't received any suitable examples to date.