Range Hood Blog

Determine Range Hood CFM in 3 Easy Steps!

Admin@Vent4Less.com (DONALD STANLEY) — Fri, 18 Mar 2011 20:59:05 +0000

To determe the CFM (cubic feet per minute) of air to be exhausted from a range hood the following three factors are considered: (a) the measured area of the kitchen; (b) the BTU (British Thermal Units) produced by the range hood and; c) the ducting between the hood and outside.

Kitchens require 15 Air Changes per Hour (ACH) to comply with the Home Ventilating Institute's building code. Follow the three steps below to calculate CFM for your range hood.

Step 1

Measure the length, width and height of the kitchen area that the range hood will service. Determine the volume of air in this area by multiplying all three dimensions together.

Example: If the area is 8 feet wide by 10 feet long by 8 feet high that equals 640 cubic feet of air that the vent hood must exchange at least 15 times in an hour. Next multiply the amount of air (640 cubic feet) by 15 which is 9600 cubic feet of air. Since CFM is measured in minutes next divide 9600 by 60 which is 160 CFM. This number is used in step 2.

Step 2

Determine the BTUs (British Thermal Units) produced by your cook top. You will find the BTU in your cook top manual or on-line. (As a rule of thumb an electric cook top produces 3,000 BTU per burner whereas a gas cook top produces 18,000 BTU per burner.) We multiply the total BTU by 0.01 and add this result to the number obtained in step 1.

Example: On average a 6-burner gas cook top will produce 108,000 BTU (6 times 18,000 = 108,000). Multiply the total BTU (108,000) by .01 which is 1,080 BTU. Add 1,080 CFM to the 160 CFM obtained in step 1 for a total of 1240 CFM.

Step 3

Use the table below to determine the equivalent duct length of stale air that the kitchen range hood must overcome.

Example: To illustrate we will use a duct run that is 4 feet of 6-inchs of straight pipe, to a 90- degree elbow, then a run of 3 feet of straight pipe to a cap. From Table 1 below the calculation is: 7 feet of straight pipe + 20 feet for the elbow + 40 feet for the cap = 67CFM. Add this number to the total CFM from step 2 (1240 CFM + 67CFM = 1307 CFM) to get a calculated CFM rating for your range hood of 1307CFM.

To comply with Home Ventilating Institute's building code in the example above you would need to install a range hood with a rating of 1307CFM or greater.

Understanding Static Pressure and Measuring Equivalent Duct Length:

In calculating the CFM required for a kitchen range hood that is ducted to the outside it is important to ensure that the range hood has the capability to move stale air throughout the duct. To do this it is helpful to understand static pressure and equivalent duct length.

Static Pressure: Inside every duct there is a constant pressure. When a kitchen range hood moves air through the duct the moving air encounters resistance from this pressure known as static pressure. Thus, an exhaust fan must have the ability to overcome the static pressure in a duct.

Calculating Equivalent Duct Length (EDL): Measuring the length of a duct is not enough to know how much static pressure a range hood must overcome. Ducts may have one or more elbows, turns or wall caps which add to the static pressure. Thus, you must calculate the equivalent duct run and not the actual duct run.

The static pressure in any duct run differs according to the material of the duct, number of elbows and turns and exterior wall cap. Below are standard values for these components.

Table 1: Duct Components & Equivalent Duct Length

Smooth metal duct: Actual duct length x 1

Flex aluminum duct: Actual duct length x 1.25 (for 4”diameter duct)

Actual duct length x 1.50 (for 6”diameter duct)

Actual duct length x 1.75 (for 8”diameter duct)

Insulated flex duct: Actual duct length x 1.50 (for 4”diameter duct)

Actual duct length x 2.00 (for 6”diameter duct)

Actual duct length x 2.50 (for 8”diameter duct)

Wall caps and roof caps: 30 feet for each cap (for 4”diameter duct)

40 feet for each cap (for 6”diameter duct)

Elbows and turns: 15 feet for each (for 4”diameter duct)

20 feet for each (for 6”diameter duct)

25 feet for each (for 8”diameter duct)

Using the values above you can calculate the equivalent straight duct length that a range hood must overcome to vent stale and counter static pressure.

This guide is provided as a service from R.E. Williams Cont. Inc. Be aware that building codes and local regulations differ from region to region and they also may change over time. We assume no liability for omissions, errors or the outcome of any home improvement project. Exercise reasonable caution and follow your current codes and regulations. When in doubt consult a licensed ventilation contractor in your area.

An Outdoor Range Hood for a Cabana

Admin@Vent4Less.com (DONALD STANLEY) — Sun, 13 Mar 2011 00:10:46 +0000

In this conversation:

Mary is interested in a wall hood over a barbeque for an outdoor cabana
How do we determine CFM requirement for an outdoor barbeque?

Mary

We are building a cabana. We will be placing a built in barbeque on outer edge of patio. There will be a tiled wall behind it. We will need an outdoor range hood. Will a a kitchen stainless steel range hood work? Is 600 CFM enough?

Customer Care

600 CFM is not sufficient over a barbeque. When the coals are simmering it could be producing (as little as) 60,000 BTU. When flaring, the barbeque could be producing 120,000 – 150,000 BTU. The CFM is calculated as 1% of the BTU. 600CFM would be adequate for simmering coals, only. 1200 - 1500 CFM is what you need for actual cooking of meat, chicken, etc.

Our Imperial line of range hoods are heavy gauge all stainless steel construction. The stainless is marine grade, the range hood will not rust when placed outdoors. However, the vent hood must be protected from direct exposure to water. In that the range hood will go into a cabana we are assuming water exposure is not an issue.

How to Determine Range Hood CFM

Admin@Vent4Less.com (DONALD STANLEY) — Sun, 13 Mar 2011 00:08:00 +0000

Discussed in this conversation:

Jim is interested in an Island Range Hood he found on eBay.
How does eBay price compare to Vent4Less pricing and do we price match?
We determined Jim’s CFM requirement is 750 CFM.
The eBay hood is overkill at 1250 CFM.
We determined appropriate kitchen island hood and saved compared to eBay.

Jim:
I am interested in this Island Range Hood 1270 CFM Imperial Series IS1900PS1-TW width 42. I can buy a similar hood on eBay for $2000. Can you match this price?

Customer Care (Donald):
We price-match any Internet-advertised price for the same island range hood. We can help you determine the actual value of the eBay offer and then compare to the Vent4Less price.

We do not sell used, returned or reconditioned island range hoods. We sell only factory new island range hoods. Our price includes the factory warranty. So our price-matching applies to new island range hoods with factory warranty. Imperial’ limits their warranty to the original buyer.

The Imperial warranty is 7-year 100% parts and labor with in home service. If any warranty issue a service technician comes to your home.

Let’s get to the Vent4Less price. Any idea how much heat (BTU) your cook top produces? If not we can help you determine the BTU.

Jim:
75,000 BTU 6-burner gas cook top.

Customer Care (Donald):
The IS1900PS1-TW you are asking about at 1250 CFM is way overkill for a cook top producing 75,000 BTU. If you use all six burners simultaneously your maximum CFM requirement is 750 CFM.

Let’s get you into an Imperial kitchen island range hood appropriate to your requirements. And save you several hundred dollars!

Jim:
ok!

Our SKU 201 (Imperial IS1942BP) in brushed stainless finish with stack kit for 7-9 foot ceiling $1760. You can see it is (externally) identical to the IS1942PS1-TW island range hood you are asking about. It produces 735 CFM, with optional power booster ($119) it produces 885 CFM. .

Jim:
OK!

How to Determine Range Hood Stack Height

Admin@Vent4Less.com (DONALD STANLEY) — Sun, 13 Mar 2011 00:10:06 +0000

In this conversation:

Lenore is searching for a thin ductless island range hood with custom stack
How do we determine required dimensions for an island range hood?
What filters does a recirculating (ductless) kitchen hood include?
How often must we replace the charcoal filter?
How do we determine stack height?
How do you determine motor freight shipping for an oversize vent hood?
If a standard stack will not fit what are your stack alternatives?
What is the warranty?
Do you offer custom range hoods?
Do you offer free shipping?

Lenore:

We need the least obtrusive stainless steel recirculating range hood possible to fit on L- shaped island. I have pet birds and this space is in their flight path. Can you help?

Customer Care (Donald):

You have birds flying inside the house? This is a new issue for us!

We have a solution for you in our model 1202. These are just 3.25 inches high measured from the base (bottom of curved canopy) to the bottom of the stack (chimney). And the birds may fly though this 3 ¼ inch space because it is a curved surface.

A secondary issue here is obtrusiveness of the stack (chimney). The stack is the part extending from the top surface of range hood upward to the ceiling. The model 1202 stack measures 13 9/16 x 11 ¼ inches which is standard. The height of the stack is adjustable to accommodate the height of your ceiling. If you set the sack height so that the bottom of the range hood is approximately 36 – 40 inches above your cooking surface you will have the shortest stack we recommend. Also, the finish of the whole enables birds to observe and thus avoid.

Since an island range hood is (typically) not adjacent to a wall, the recommended dimensions of the range hood must be slightly wider than your cooking surface. (Width is the left-to-right measurement). The recommended depth of the range hood is similarly slightly more than your cooking surface measured front-to back. (Depth is the front-to-back measurement). For your requirements we recommend the range hood in 42” width.

With our standard stack (for an 8-9 foot ceiling) the 42” recirculating (ductless) model is $1091. We have stack options that are longer or shorter, if you need.

This range hood has two filters: aluminum mesh screen at bottom and charcoal (as filter for recirculating air) above the this and thus unseen. For cleaning the aluminum mesh goes in the dishwasher. The charcoal must be replaced 1-2 yearly, depending on your style of cooking. Extra charcoal filters are $45 each.

Give us your zip code we will quote shipping. Due to size and weight, this range hood must ship via motor freight which is the reason we cannot offer free shipping. However the rates change daily and we use a number of carriers to ensure you receive the best rate. We do not mark up shipping. With a bit of research we will likely find less expensive shipping than that quoted on the site today..

We have these island range hoods in stock for same day shipping. Double click (or control click, or cut/paste into your browser) links below for complete information regarding our model 1202

http://www.vent4less.com/m8/1202--island-range-hood-600-cfm-windster-series-hi.html

Lenore:

We do not have the space for a standard stack. What do you suggest?

Customer Care (Donald)

The recirculating hood we discussed this morning requires the stack. This is because the vent is located at the top of the stack via side louvers.

The minimum stack height then is the height of a single stack piece; you don’t need to use both pieces. The shorter stack extends 18” above the range hood.

Alterative Stack Solutions

We can provide an island hood stack manufactured to your exact height requirement.

We can also provide an island range hood without stack, if the distance between the bottom of the range hood and ceiling will be within 28-42 inch range. This is our SKU 201 (Imperial IS1942BP). The 201 height is 6 inches and produces 430 CFM (airflow).

If the range hood must be more than 6” high to achieve the minimum height above cook top without stack this is our SKU 204 (Imperial ISP1942BP). The 204 height is 12 inches and produces 750 CFM.

Subtract six inches from your measurement which is the height of the 201; twelve inches for the model 204. Either may be controlled with a remote wall switch (option) or twist knobs on the bottom of the unit (standard).

http://www.vent4less.com/6.html?m8:search[sel_text52]=42;search[group]=1223841;search[nested]=0;search[fuzzy_sku]=1;srredir=m8_view_item.html

http://www.vent4less.com/m8/204--island-range-hood-750-cfm-imperial-series-isp1900ps.html

Warranty

Our price includes the industry's only 7-year 100% parts and labor plus in-home service warranty. If any warranty issues during the first seven years a service technician comes to your home. 2011 is the 50th year Imperial has been crafting range hoods in the USA. Vent4Less offers top-of-line quality plus Internet-direct pricing.

Custom Range Hoods

A significant part of our business is custom range hoods. If you are seriously considering these we will visit the factory and obtain a price for these as a recirculating (e.g. custom) hood.

We will subtract the stack charge (now include in the price) then add for charcoal filter and exhaust louvers, which is the customization required here.

Free Shipping

For a limited time we are offering free shipping on all Imperial kitchen island range hoods.

How To Determine Range Hood Dimension & Filter

Admin@Vent4Less.com (DONALD STANLEY) — Sun, 13 Mar 2011 00:11:41 +0000

Discussed in This Conversation:

Bruce is searching for a Range Hood Insert
How do we determine required dimensions for the range hood?
How do we determine required required CFM (airflow) for the range hood?
Difference between baffle and screen filters.

Bruce:

I need a kitchen range hood for use with a 42 inch range. The range has 6 burners and produces 62500 BTU.

Customer Care (Donald):

Hi Bruce, let’s find what you are looking for.

Use SEARCH dropdown (top of page), select “wall range hood” and size “42”.

6250 BTU means we need something with 625 CFM, about.

When you have the results of search, any range hood of 625 or more will work.

We can discuss the results page when you have it on your screen.

Bruce:

Actually, I need either a range hood insert or a wall hood.

I will place wood over the range hood.

Customer Care (Donald):

A range hood insert is far less expensive, and functionally the same.

Do you have a cabinet to put the insert into?

Bruce:

The cabinet maker will fabricate a cabinet.

Customer Care (Donald):

Well then, you are good to go with an insert!

Under search drop down again, select INSERTS and 42, then push search button

Bruce:

Do I need to get the same dimension as cook top 42 by 24 inches?

Customer Care (Donald):

Yes, the range hood dimensions must be at least as wide and deep as your cook top.

We recommend Imperial C2000PS-28 (our SKU 313), for your requirements.

Click the photo, then the SCHEMATIC tab halfway down page, for dimensions.

Actual dimension are either 40 3/8 or 46 3/8 wide, by 28 1/4 deep.

Bruce:

OK thanks again, I found it.

Customer Care (Donald):

If you want stainless steel baffle filters then the insert is 10" high.

With standard stainless screen filters then the insert is 6" high.

Bruce:

What is the difference between stainless screen and stainless baffle filter?

Customer Care (Donald):

Let’s look at some photos to answer that.

Click on WALL dropdown menu at top of page.

Models 1710 and 701 show baffle filters.

Models 703 and 709 show screen filters.

Baffle filters are made of stainless steel; screen filters are made of aluminum.

Both baffle and screen filter types are dishwasher safe.

To thoroughly clean either, just drop in your dishwasher.

Baffle (hard surface) can be easily cleaned between washing, with damp sponge.

Baffle subtracts about 100 CFM from airflow, and adds about $110 to cost.

Professionals seem to prefer baffle filters.

Bruce:

OK, I will make my decision and enter my order on your site today.

Thank you again.

Customer Care (Donald):

You are most welcome!