# Ducting Range hood down through crawlspace



## mcelhane

Due to multiple problems venting to the roof,  I would like to vent my range hood down through the back wall, into the crawlspace, and out the crawlspace (exit should be about 1 foot above ground).  This would require a 3 1/2" x 10" right angle at the back of the range hood (the hood exhausts to the back), a 3 1/2 x 10 straight duct down through the stud wall, another right angle in the crawlspace, a transition to round ductwork (7 or 8) and then out to crawlspace wall.

The building inspector said that my approach is against code unless I purchased a downdraft cooktop and connect to it.  I am confused, where in the code does it prevent me from doing this for a range hood?  (Please, do not suggest the downdraft cooktop - those things do not work - a recirculating range hood works much better than those.)

Thanks.


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## cda

Welcome

It may be Monday till you get some responses

You should ask the inspector for a code section he is referencing that does not allow it.

Do you know which code and edition you are under?


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## cda

from the 2009 IRC

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 and shall be equipped with a backdraft damper. 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; and

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

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

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 M1507.3.

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.


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## Msradell

I also read through the IRC and based on what I read and what CDA posted I see nothing in the code that prohibits someone from doing what you're proposing. The only caveat would be the calculated length of the ductwork because different shapes and sizes as well as corners increase the effective length of the ductwork. As long as the length was within the manufacturers recommendations you should be okay to go unless the inspector come up with some other code reference that's different! Knowing what code version you are under would probably help.


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## cda

Msradell said:
			
		

> I also read through the IRC and based on what I read and what CDA posted I see nothing in the code that prohibits someone from doing what you're proposing. The only caveat would be the calculated length of the ductwork because different shapes and sizes as well as corners increase the effective length of the ductwork. As long as the length was within the manufacturers recommendations you should be okay to go unless the inspector come up with some other code reference that's different! Knowing what code version you are under would probably help.


The only thing I can think of is possible grease build up, and how to clean it???


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## fatboy

Manufacturer's spec's, if they don't prohibit it, the code doesn't, as far memory recall goes. As said, politely ask for a code reference.

Welcome to the forum.....


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## Msradell

cda said:
			
		

> The only thing I can think of is possible grease build up, and how to clean it???


As long as it doesn't go down and come back up creating a low spot I don't see how it's any different than going up and out. As a matter fact it may be better because the grease would never come back into the residence, it would flow toward the outdoors end.


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## ICE

cda said:
			
		

> and how to clean it???


A long haired cat would do the trick.  He did say that he was planning on 7"to 8" duct.  Might take a few runs....maybe even a few cats.


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## MASSDRIVER

ICE said:
			
		

> A long haired cat would do the trick.  He did say that he was planning on 7"to 8" duct.  Might take a few runs....maybe even a few cats.


Admirable outside-the-box thinking, But not needed. Never in the recorded history of mankind has a residential range hood duct ever been cleaned.

Never.

Brent.


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## MASSDRIVER

!@#*^#%#*@(@


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## mcelhane

Thanks all that replied.  Called the inspector again, and apparently, he was mistaken.  Imagine that!  Thanks again, I wanted to be sure that I had no missed something in the code.


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## ICE

mcelhane said:
			
		

> Called the inspector again, and apparently, he was mistaken.  Imagine that!


The inspector wasn't mistaken, you asked the question wrong.


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## cda

mcelhane said:
			
		

> Thanks all that replied.  Called the inspector again, and apparently, he was mistaken.  Imagine that!  Thanks again, I wanted to be sure that I had no missed something in the code.


All you have to do is ask!!!

And since we saved you tens of thousands of dollars, If you would like to support this web site, it would be nice. This is a self supporting site comprised of different people related to codes and construction. Trying to help each other out, and home owners that have questions::::

http://www.thebuildingcodeforum.com/forum/payments.php


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## cda

mcelhane said:
			
		

> Thanks all that replied.  Called the inspector again, and apparently, he was mistaken.  Imagine that!  Thanks again, I wanted to be sure that I had no missed something in the code.


All you have to do is ask!!!

And since we saved you tens of thousands of dollars, If you would like to support this web site, it would be nice. This is a self supporting site comprised of different people related to codes and construction. Trying to help each other out, and home owners that have questions::::

http://www.thebuildingcodeforum.com/forum/payments.php


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## mtlogcabin

Just double check the size of the fan that it will cover the distance and number of elbows you are using. I bet you will need 500 CFM or larger to accomplish what you want to do.


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