Hood placement for gas range

Question

Most appliance companies recommend a distance between 24" and 30" between the range and the hood. However, is this based in anything concrete? I mean, the hood should be powerful enough the provide enough suction for an entire room, plus you can install hoods in the ceiling which is a lot more than 30" from a range, so I'm just wondering if there's something I've missed.

I have an Ilve Nostalgie range and I want to install a Noblesse hood. The contractor says that the hood won't work properly if it's not installed at 30" height maximum, but my Ilve supplier says that it doesn't really matter. Any thoughts?

Answer 1

There are two simple factors with opposing relationships:

• Work clearance
• Vacuum effectiveness

The manufacturer wants the hood as close as possible so it's more effective at scavenging gases, but they know you need clearance to move and cook. That's really it. Fire danger isn't much of a factor until the hood is mere inches from the burners, and who's going to do that?

Regarding reduced effectiveness at greater heights, I'd expect an accelerating reduction in scavenging with height. If you think of your hood's area as a portion of the surface of a sphere centered on the stove top, the further away you go the smaller that is as a portion of the sphere's surface¹. It shrinks substantially as the effect of local breezes increases. (Simply walking by pulls a lot of the fumes along with you, out of reach of the hood².)

Therefore, that 30" number isn't "concrete", but it's notice that you lose a lot of exhaust function if you go beyond it. There's not much science to be applied due to the great potential for variation in local conditions³. Any claims to numbers would necessarily assume averages from a large range of values.

---

¹ It's an oversimplification for sure, but let's take a look using the hood's box area (which may not even be appropriate; the duct opening might be a better reference). The area of a sphere at 24" radius is 1809.6 in². The portion of a range hood of say 20"x30" is 3.31%. If you move out to 30" it drops to 2.12%. That's a proportion reduction of ~36%. Move out to 36" and you're down to 1.47%, or another 30.6% smaller and less than half what it was at 24". The reduction in effectiveness as a result is compounded by dynamic air movement in the room and time.

² Beyond its event horizon, if you like.

³ HVAC type and location, room size and shape, window usage and location, door usage and location, ceiling height, human activity, etc., etc. It quickly becomes a study in chaos theory akin to predicting the weather.

Answer 2

A web-search on "why must a range hood be 30 inches above the range" reveals several results, mostly from manufacturers' websites, explaining that the lower limit is defined by the heat generated by the range, and the upper limit is defined by how much suck the hood blower has and how much range air will be vacuumed up. I could not find a scientific paper on the subject, but there is likely science behind it.

The biggest concern on where to place a particular hood code-wise is using a UL/ETL/equivalent-listed hood and following the manufacturer's instructions. A listed hood has been tested for safety, and the manufacturer's instructions will reflect the safety limits determined by the listing authority.

Mounting the hood outside the instructions' measurements (too low, too high) will make the installation not up to code and not covered by your house's insurance company in the event of an accident.