help in cooktop down draft ducting

9 years ago

Hi,
I am posting this here because HVAC folks know more about ducting.

We replaced our island downdraft cooktop and the new cooktop's vent is in different location and lower than the original one.
I am trying to figure out best way to connect them. I tried using the semi-rigid flexible duct but the turns are too tight for it and I am not being able to make connection. The tube tears. Maybe I am not doing it properly.

The vent has a square to 6 inch round transition. And the floor I had to place a 6 inch to 5 inch reducer. Both of which are taking up lot of height.

I am attaching the photos below.

If anyone know how I can do it, please let me know.

Thank you very much in advance.

Featured Answer

sgw_ma
Original Author

9 years ago

Thank you Vith and everyone else. yes, I had to become creative.

I had to make several modifications to get things to fit.

I had to shorten the square to round adapter by cutting it.

Shorten the 6" to 5" adapter by removing the 6" collar.

I had to take off pieces of the 2 5" elbow fittings appropriately.

Taped it well.

It is more aerodynamic then two 90 degree turns.

You can see in photos attached. Without and with taping.

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Comments (9)

mike_home
9 years ago
last modified: 9 years ago
Have you tried the plastic dryer vent duct.? The fact it is plastic should not be a concern since the air is cool.

You could also try removing the 6 to 5 inch transition. Then see if you can install the rigid vent. If it fits then cut several one inch slits at the end of the duct connecting to the 5 inch vent. You may be able to then crimp the semi rigid vent with a vent clamp. You could use some teflon tape to seal it.

You could also come down from the top connection make a turn and snake the vent up into the cabinet and then make a downward turn and connect to the vent. It will be ugly and take up cabinet space but it should fit.
sgw_ma
Original Author
9 years ago
last modified: 9 years ago
Thank you Mike.

The instructions say not to use non-metal flexible ducts because they cause airflow restrictions so I did not use any non-metal flexible ducting.

I will try the direct attaching method without the reducer and see if I can make metal flexible duct fit.
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mike_home
9 years ago
See my ugly suggestion above.
weedmeister
9 years ago
I'm not sure the exhaust off a cooktop is going to be 'cool', though it is a relative term.

Maybe two 90* elbows with a short length of pipe in between?
sgw_ma
Original Author
9 years ago
Thank you Mike, that can be a kludge option.

Thank you weedmeister, I think two 90*elbows might not fit. I will check it out though. The center to center in x and y are about 6 inches only. And the height open is about 3.5 inches.

I am thinking that two 45* elbows might connected with short pipe be able to work. I have to try it. This is for 6 inch diameter ducts which I prefer. I might have to move to 5 inch diameter elbows which should have smaller bend, height and length. I would have to move the reduced to connect to the square to round transition then.
Vith
9 years ago
last modified: 9 years ago
Metal flex sucks to work with (does not conform to difficult bends the same way non-metal does) but probably required due to the range heat.

Another option is a different boot for the range hood that has90 degrees built in, then use another elbow to go down with it. The one in the link is for a 10 by 3-1/4 opening make sure that is correct if you go that route. This option is not very aerodynamic so I am thinking the two 45's would be better. Or perhaps one 45 with a small bit of flex.

Going to have to get creative lol

Make sure you seal the joints with some foil tape.
sktn77a
9 years ago
Nice job! Yes, that 5" to 6" adapter looked like the best place to tackle it.
sgw_ma
Original Author
9 years ago
Thank you.