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Over the Range Microwave range hood help

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  • Feb 8th, 2013 8:47 am
[OP]
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Mar 13, 2008
145 posts
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Calgary

Over the Range Microwave range hood help

I'm planning to replace my GE Over the Range Hood Fan Microwave combo and started doing some research on what alternatives I have and how to remove the current unit and the size of the current pipe.* Then I found a unit (see following pictures) attached to the duct.* I have no clue what it is and this unit wasn't mentioned on the installation instruction either.* Anyone shed some light would be greatly appreciated.*


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13 replies
Deal Expert
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Dec 11, 2005
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It looks like some kind of water pump seeing how it has what look to be low pressure inlet and outlet hoses but I have no idea why it would be running into the duct like that???

Very interested to see who responds!
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Oct 22, 2007
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It almost looks as though one inlet/outlet male connection isn't complete; correct me if I'm wrong. The only thing that comes to mind is some sort of fire suppression system, but I'm not sure how it would be triggered or what liquid would be supplying the duct work.

I would investigate further and see where the what seems to be a 1/4" clear tube goes to as well as whether there are any other hidden rough ins. It almost seems as though the red wire is a low voltage line to supply power for some sort of solenoid.
Deal Addict
Jun 16, 2009
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Woodbridge
WHo so ever has done ( if done correctly ) has done a very good job . From pic it looks like a pressure switch is attached to hood . Which means in case your vent is blocked for any reason it should automatically shut off the fan .
nsfour wrote: I'm planning to replace my GE Over the Range Hood Fan Microwave combo and started doing some research on what alternatives I have and how to remove the current unit and the size of the current pipe.* Then I found a unit (see following pictures) attached to the duct.* I have no clue what it is and this unit wasn't mentioned on the installation instruction either.* Anyone shed some light would be greatly appreciated.*


Image

Image
Deal Addict
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Dec 12, 2006
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Messed Up Area
Looks interesting, anyway of telling us the markings on the block, as can't really see in images...
[OP]
Jr. Member
Mar 13, 2008
145 posts
22 upvotes
Calgary
Thanks guys to spend your time to read and respond. Greatly appreciated! I will try to get the markings on the block and post again tonight. The builder did it as the unit came with the purchase of our house. My concern is that if I leave that unit on and switch my range hood, would that become a problem? I assume the red cable somehow connects back to the microwave/fan unit to trigger the suppression if the vent is blocked.
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Oct 22, 2007
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We're not saying it's related to fire suppression as that's only a guess on my part. Fire suppression in a kitchen exhaust hood normally function to close the exhaust vent to not allow fumes or fire to spread as well as apply what ever chemical or liquid to help put out the potential fire. We're not sure exactly how if any this is done with this set up. Let us know what you find out so it may help others should they have a similar device.
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Mar 28, 2008
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ON
Pressure (differential) switch...Not smoke detector/suppression. The fitting with the tube gets the duct pressure and the open fitting gets the room pressure, a difference in pressure between operates the switch. It could be to shut it down....More likely for makeup air (air intake to replace exhaust air), so there isn't a vacuum issue and things like backdrafting.


EDIT: With the size of range hoods now, I think makeup air is greatly overlooked (both because of issues and not getting the capacity from your hood). Im just not up on HVAC codes to specify the actual rules.
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Nov 18, 2005
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Kitchener
do you have a gas range? this pressure switch is normally installed to ensure the exhaust hood is venting properly when using a natural gas stove
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Dec 9, 2003
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Its a Pitot tube connected to an airflow switch. Either to turn on the makeup outdoor air when the fan is on or else to turn off the fan if the flow is blocked. Normally the former. They are useless because they plug up with grease.

And since most microwave fans are <200cfm they are pretty useless in removing air an therefore dont really need a makeup air system
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Mar 28, 2008
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Cough wrote: Its a Pitot tube connected to an airflow switch. Either to turn on the makeup outdoor air when the fan is on or else to turn off the fan if the flow is blocked. Normally the former. They are useless because they plug up with grease.

And since most microwave fans are <200cfm they are pretty useless in removing air an therefore dont really need a makeup air system
Microwave fans at HD are 300-400 cfm, but they don't usually put that out, mostly because of lack of makeup air.
[OP]
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Mar 13, 2008
145 posts
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Calgary
sprdave wrote: Microwave fans at HD are 300-400 cfm, but they don't usually put that out, mostly because of lack of makeup air.
Thank you guys. After some research, I finally have a little bit of clue about this. My only concern is that if I'm to install a more powerful range hood (700-800 cfm), do I need to worry about this airflow switch?

Just a little more background about the setup. The switch has one end going into the range hood exhaust duct (as shown in picture), and the other end (the red cable) goes all the way to my furnace system in the basement.
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Mar 28, 2008
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nsfour wrote: Just a little more background about the setup. The switch has one end going into the range hood exhaust duct (as shown in picture), and the other end (the red cable) goes all the way to my furnace system in the basement.
Makeup air. Should start the furnace fan (notice the furnace come on when you run the hood?). There should be a duct from the furnace ducting from outside, possibly with a damper. Installing a more powerful hood makes it even more important, and may even need more.

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