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Range Hood Ventilation Is A Many Splendored Thing, But There’s No Great Solution!

Faced with making the choice about which range hood to select, most people gravitate to the one that looks the best and that fits within their budget.  The reason to have a range hood is for good indoor air quality, so paying attention to the technical side of ventilation is important as well.

What kind of range hood Range hood to select?

Hoods come in many flavors and styles, but generally there are four types:

  • Wall Hoods
  • Island Hoods
  • Downdraft Hoods
  • Recirculating Hoods

The best location for a range hood is against a wall; Wall hoods have a much better chance of catching the vapors from cooking because the wall creates a natural containment for the fumes and they have one less side to escape from.

Island Range hoods look great, but as you might expect fumes can escape from all 4 sides and this compromises their performance.

Downdraft range hoods are fighting against the natural tendency of fumes to rise.  In the long run, they don’t win and aren’t very effective either.

Recirculating hoods are generally regarded as ineffective.   Recirculating hoods typically have a charcoal filter to deal with odors and another filter for grease, but because they don’t exhaust the air, they are just pitching the potentially harmful cooking vapors back into the house.

Size of hood

The Home Ventilation Institute HVI certifies the ventilation rate for home ventilating appliances like range hoods. Make sure there is an HVI label on your hood.

HVI recommended rates for ventilation:

Width of hood against a wall

2.5 feet (30 in.)

3 feet (36 in.)

4 feet (48 in.)

HVI recommended rate

250 CFM

300 CFM

400 CFM

Minimum

100 CFM

120 CFM

160 CFM

Or, another way to look at it….

Location Of Range

HVI recommended ventilation rate

per linear foot of range

Minimum ventilation rate

per linear foot of range

Against a wall

100 CFM

40 CFM

In an island

150 CFM

50 CFM

Berkley lab has studied range hood fans from the perspective of capture efficiency.  They have looked at how well hoods actually pick up the fumes.  The good news is most hoods are pretty good at capturing fumes, the bad news is that is only if you cook on the back burner.   Capture efficiency is a great metric, but it’s not one you will find on a range hood yet.  Additionally, they recommend the hood be as wide as the range and ideally as deep as the cooktop.

Building Code

Some range hood fans provide a huge amount of fan power, clocking in up to 1,200 cfm.  The industry says it is to vent the heat, which is legitimate, but to have a fan large enough to suck up mice creates some problems.  Namely, that you are throwing out a lot of good conditioned air and air that goes out must come back in.  The code requires​ that fans that exhaust over 400 cfm be provided with make-up air.  Let’s just say this gets tricky to do well.  It’s a lot easier if the cfm power of the range hood is under 300 cfm.  Be sure to check with your local authority on this, some jurisdictions have made local modifications to the code, namely requiring make-up air at rates lower than 400 cfm.

2012 International Residential Code : Range Hoods

SECTION M1503

RANGE HOODS M1503.1

General. Range hoods shall discharge to the outdoors through a single-wall duct. The duct serving the hood shall have a smooth interior surface, shall be air tight, shall be equipped with a back-draft damper, and shall be independent of all other exhaust systems. Ducts serving range hoods shall not terminate in an attic or crawl space or areas inside the building.

Exception: Where installed in accordance with the manufacturer’s installation instructions, and where mechanical or natural ventilation is otherwise provided, listed and labeled ductless range hoods shall not be required to discharge to the outdoors.

M1503.2 Duct material. Single-wall ducts serving range hoods shall be constructed of galvanized steel, stainless steel or copper. Exception: Ducts for domestic kitchen cooking appliances equipped with down-draft exhaust systems shall be permitted to be constructed of schedule 40 PVC pipe and fittings provided that the installation complies with all of the following:

1. The duct is installed under a concrete slab poured on grade;

2. The underfloor trench in which the duct is installed is completely backfilled with sand or gravel;

3. The PVC duct extends not more than 1 inch (25 mm) above the indoor concrete floor surface;

4. The PVC duct extends not more than 1 inch (25 mm) above grade outside of the building; and

5. The PVC ducts are solvent cemented.

M1503.3 Kitchen exhaust rates. Where domestic kitchen cooking appliances are equipped with ducted range hoods or down-draft exhaust systems, the fans shall be sized in accordance with Section M1507.4.

M1503.4 Makeup air required. Exhaust hood systems capable of exhausting in excess of 400 cubic feet per minute (0.19 m3/s) shall be provided with makeup air at a rate approximately equal to the exhaust air rate. Such makeup air systems shall be equipped with a means of closure and shall be automatically controlled to start and operate simultaneously with the exhaust system.

Noise

​Range hood fan noise is measured in Sones. The lower the sone rating the better because using a quiet fan is much more pleasant than using a loud one and a quiet fan is a lot more likely to see regular action than a fighter jet style fan. The people at Berkley Lab suggest a sone rating less than 3.    The relationship of sones is linear, so 1.5 sones is half as loud as 3 sones.

Ducts

Range hoods are connected to ducts, make sure the duct actually connects to the outdoors. It’s a no-no to vent into the attic, and it’s a waste of money to not vent. Make sure the ducts are sealed and it’s wise to read the installation instructions yourself to make sure that the duct is installed according to the manufacturers recommendations.

High Performance Homes

The job of a range hood is to ventilate. Range hoods suck air out of the house as part of their job. What goes out must come in and if a source of fresh air is not provided, it will be sucked in through every available crack in the house. That is unless you provide a controlled source of fresh air, which in technical lingo is called make-up air.

There are two approaches to range hood ventilation in a tight house.  An approach used in many passive houses is to use a recirculating hood and locate an exhaust duct for the ERV or HRV in the kitchen.  The benefit of this approach is that it does not poke extra holes in the house, which are considered leaks,  and relies on the heat exchange system to efficiently exhaust and provide make-up air.  There hasn’t been any testing to verify if this is a good approach and code officials may not be on board with it.

The second approach is more standard.  Poke the hole in the wall and deal with the consequences of lost energy.  Code officials should have no problem with this.

Adding pre-conditioned make-up air near the range hood is probably a good idea in a tight house to make sure that ​indoor air quality is preserved.  This should be reviewed with the mechanical engineer or designer.

The Perfect Hood

The perfect range hood should be located on a wall, be as wide and deep as the range top, be quiet, fall within the HVI recommended cfm range, be ducted to the outdoors, have proper make-up air, do an excellent job of capturing fumes and look good.   And that’s just to get the indoor air quality thing right.  Energy efficiency is another matter, keeping the cfm’s low helps, but poking a hole in the wall is an energy penalty.   More solar panels anyone?  I favor the approach of installing a range hood for best indoor air quality, taking the energy penalty and compensating for it with more renewable energy.