I don't know where you are, but in FL "crawlspace" is another word for attic, because that's all they mostly are. Is it possible that's what they mean?

That's a new one. I think it would put cooking odors and moisture throughout your entire house. Yes, I'd wonder what other "creative" things they did to this house.

Everywhere I have lived crawlspace is underneath the house, where you don't have a basement. I've never heard it used to mean attic.

In FL it can mean either one, but since post-WWII houses are usually built on slab here, nowadays the latter meaning is much more common. Under-house crawlspaces existed back when houses had real attics that you walked up stairs to get to and could stand upright when you got there. Those houses were usually on a slightly raised foundation to allow air to circulate beneath and also in case of flooding.

Anyway, I'd be curious to hear from anon if this is (hopefully) a possibility. Otherwise, I'd have to agree with Anglophilia--time to worry.

Considering the OP used the word "down" a few times, I am thinking we're talking about the "lower" crawlspace definition.

And yes - this is downright bizarro. I would anticipate that being 100% ineffective.

That’s a PASS on that house. If they’d do that, there are likely stupider things that you can’t see.

I thought that writersblock was suggesting that the OP may have misunderstood what the builder meant when they said crawlspace; that s/he understood the crawlspace under the house when the builder meant attic crawlspace.

If the duct has 3 90 degree bends and runs an extra 7 feet to get from the hood down to the crawlspace under the house, yes it's a problem. It's bad system design and will adversely affect the performance of the fan. CFM rating is based on a specific static pressure, and the longer your duct and the more bends it has, the worse the performance will be (lower CFM).

But if there's any chance that there was a miscommunication between you and the builder, I would try to get clarification before I wrote off the house.

I thought that writersblock was suggesting that the OP may have misunderstood what the builder meant when they said crawlspace; that s/he understood the crawlspace under the house when the builder meant attic crawlspace.

Yes, exactly. Thanks, cawaps.

When I moved into an upper floor unit in my condo, I became knowledgeable about the ventilation ducts from people's range hoods because I had to move a couple of them and not add to their equivalent length.

I determined that the duct length from my lower floor unit was 40feet in a purely vertical direction and had three 90 degree elbows for a total of 55 feet equivalence.

The range hood I had had a 60 foot total allowable length. It was noisy, but it did work because it (barely) met the total overall length requirements.

I am not recommending maximizing duct length and the number of bends by any means, but I am just pointing out that you can't assume that it won't work just by looks. You have to calculate. And a sealed duct should still carry cooking smells and vapors out and not allow them to "leak" into the house. Anecdotally I think that since grease is heavy there will be some settling of grease on long horizontal runs of ducts internally toward the outlet.

I've seen this in homes that were built with a downdraft and retrofitted with a wall hood. Works okay (not great) but I can't imagine building it that way on purpose!

I took out a downdraft duct like this that ran the length of the house and replaced this with an island hood but it took 4 bends to get it the short distance out of the house.

OP here. Thanks for the feedback. This is in NC where "crawl space" means the area below the house when it does not have a basement. In NC attics are called attics. Builder definitely says this goes through the crawl space and vents to the outside.

And this is new construction, so no, it was not a downdraft retrofit.

Even if they calculated the length of the ductwork correctly to account for all of the 90 degree turns, it still seems like the majority of folks think this is a questionable building/design choice, and I tend to agree.

Test it out. It might be okay.

The next question is, where would it have gone otherwise? If the builder ignored several obvious shorter routes for the crawlspace, maybe it is a questionable decision.

But if it goes through the crawlspace to avoid blasting someone in the face on a deck or patio or to avoid a vaulted ceiling upstairs from the kitchen or some other convoluted path, maybe it is the better of several not great options?

(My house has corner to corner glass on both front and back elevations on the first floor and a glass wall with exposed sheathing ceiling on the third floor. (And common wall houses on each side). There are very few places to run any ducts.We are fishing a vent duct straight up and through a knee wall that avoids any of the glass walls, but my neighbors have one duct that bumps out in front of one of these windows, and another vent that exits exhaust right next to their front door. Not attractive. We are able to run this duct relatively straight because we are demoing back to the masonry wall between houses.)

My brother just installed 2 Range Hoods this way going down & out through the crawl space to the outdoors, it is becoming more commonplace to do this, I had never heard of it before & researched it, although I should have known he knew what he was doing, he does a lot of this work & is exceptionally intelligent. I was interested because I want to put in a range hood but don't want to put anan opening in my very expensive metal roof, my crawl space underneath is 5' deep & this is the only way I would consider a range hood that vents outdoors.

We have had to do this up-down-sideways-out scenario in renovations where there just isn't a closet or space upstairs to take a vent though to the roof. As posted above, you just have to calculate how many turns the system and length will allow, and I'd suggest you stay well inside of that limit for good air movement. If I were designing a new house I certainly wouldn't plan it this way, and if the plans called for it I'd wonder more about the designer/architect than about the builder!

Nobody has mentioned the reason this is sometimes a good way to do it. It allows you to use a remote blower which makes your hood much quieter. Yes it could be simpler to go up with it, but not everyone has an attic for the fan, or the ability or desire to put another penetration through their roof.