Venting Pro-Style Cooktop
I have a Electrolux 6-burner cooktop that has a maximum output of 70,000 btus. The store that I bought it from recommended a Zephyr Tornado I (600 cfm) for the ventilation system with 6" ductwork. I live in an old house and the old kitchen duct is a 3.25 x 4. This duct is obviously too small, so the only way to vent is horizontally through the upper cabinents. The way that is shortest w/less bends (1-90, 3-45's and end cap - 10' total length) will come out about 2' from an on demand water heater vent. Another route is to have 3- 90's, 2-45's, end cap w/18-20' total length will come out at the base of the house. The manufacturer recommends not exceeding a total of 100 equivalent feet.
Different companies have recommended anywhere from 6" - 10" duct work and yes or no to whether to have fresh air brought in.
I am confused. Any ideas? Also if you increase the size of the recommended duct work can you extend the length of the duct and will it make it quieter?
Manufacture should have specs for duct sizing depending on lengths and bends. I would use those.
As for fresh air, do you have any gas burning appliances or open fireplaces in the house. A 600 CFM fan will take alot of air out of the house and could very possibly cause backdrafting of other appliances. You do not want to put your house into a negitive pressure.
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For 600 CFM, depending on the style of fan and how much static pressure is allowed, you may want at least 8 or 10". or it will be noisy and use more power. The installation instructions should recommend a size.
If you are removing 600CFM.... then 600CFM WILL find it's way into your home. Better to bring that fresh air into a place where it can be filtered and conditioned.
If you don't add some type of ventilation, the fan may struggle to run at it's full capacity, and things like bathroom fans, B-vents (gas appliances), chimneys, may begin to event backwards.
You house being old, will simply feel very drafty when the vent fan is running and become very humid in the summer.
I'd suggest a large, passive fresh air intake with a damper. My ductilators says you'll need a 12" round or something like a "8x14" rectuagular duct to get enough make-up air using your HVAC system.
You would then need the "fan" contacts on you HVAC to come on when the vent hood comes on as well as opening the fresh air damper. You'll want a large pleated air filter installed on the make-up air line to prefilter the air. You will also need ot insulate the duct to prevent condensation.
Some of the IAQ experts may have some good idea how to balance the air in your home.
Ultimately a commercial style range and hood can result in commerical style HVAC solutions.
10" is your typical size on most brands from 400-900 cfm.
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