Optimal use of remote range hood blowers

There are three basic forms of range hoods blowers:

• Internal range hood blower - the range hood blower is located inside of the range hood canopy
• Inline to the duct run - the range hood blower is located somewhere along the range hood exhaust ducting
• External to the range hood - the range hood blower is located either on the roof or on an external wall

Internal range hood blower

External range hood blower

Inline range hood blower

If the cooking equipment - the stove or the range dicatate (based on the btu to cfm calculation that can be found on posts in this blog) that around 600cfm is required then there is not a great deal of benefit to be achieved by placing the range hood blower remote from the range hood canopy

Noise is one of the main reasons why remote blowers for range hoods are installed. If the range hood blower, whether inline or external is close to the range hood very little benefit in term so of noise reduction will be achieved.

An external blower mounted on the wall directly behind the range hood without any bends in the duct run will not help the noise a great deal.

For optimal noise reduction from an external blower there should be at least one 90 degree bend in the duct run.

For optinal noise reduction a duct silencer system can be placed in the duct run.

Duct silencers

How wide should the range hood be

The range hood should as a minimum cover the width of the range. The reason for this is that the hot vapours from the range expand as they billow up. Under ideal circumstances the range hood should be wider than the range by 3" either side - however this is not always possible.

Wall Range Hoods:
Wall range hoods should as a minimum be the same width as the range top

Island Range Hoods:
Island range hoods should as a minimum be 6" wider than the range top. The reason is quite logical - island range hoods are exposed to cross drafts in the kitchen from ventilation systems and even people moving around.

Here is a picture of a 12' wide range hood - the range top is a 30" induction cook top and we provided a 600cfm internal vent blower with stainless steel mesh filters directly over the induction cook top - 30" wide. The remainder of the island range hood underside was custom fabricated stainless steel panels with lighting. The lighting is controlled by two dimmable range hood light controls - one controlled the kitchen hood lighting above the induction cooktop and the other rangehood light controlled the island rangehood lights on the perimeter:

Link to range hood design information

Range Hoods and Make Up Air Systems

Why does your range hood need a make up air system


What is make up air for range hoods

High cfm range hoods take out large volumes of air from the building space. If this air is not replaced at the same rate that it is expelled, the building will experience a negative pressure (the air pressure outside the building is greater than the air pressure inside the building).

A few common indicators of a negative air pressure problem are:

•Exterior doors are hard to open

•Drafts around doors and windows

•Range hood may not be drawing vapours properly

•Smoke from a wood burning fireplace is pulled into the room

Custom Island Range Hood - Claret Red with polished brass trim

A make-up air system replaces the air that is expelled by a building's exhaust system, maintaining the proper balance between inside and outside air pressures while also providing many other benefits:

•Provides conditioned air back into the home - cooled in summer, warmed in winter, de-humidified

•Aids the proper functioning of range hood exhaust fans

•Improves air quality

•Stops backdrafting of fireplaces, natural gas fired furnace and hot water tank exhausts

In the colder northern hemisphere where the windows and doors are closed through the winter and where the homes have become increasingly air tight building inspectors are paying more attention to the need for make up air where high powered range hoods (some areas as little as 600cfm) are installed.

Range Hood Terminology

Common Range Hood Terms

A very common term used in ventilation is cfm – cubic feet per minute – this typically measures the volume of air that the hood can process in 1 minute and is an important metric in sizing the ventilation to your particular cooking environment.make up air. In the North of our great continent our new homes are almost 100% airtight – we make them so to keep drafts out. In the middle of winter everything is shut tight – we are cooking up a feast and we have our hood fan running on maximum and its sucking out 600cfm – that is 600 cubic feet of air every single minute – if our home is airtight where is the replacement air coming from – there is only one place it can come from and that is the exhaust pipes used by our furnaces, water tanks and fireplaces that are working at expelling carbon dioxide and a ton of other lethal gases – the result is that we fill our house up with poisonous gases – there have actually been a few deaths from this. The only way to combat this and still keep our beloved kitchen ventilation is to install a make up air system – a system that replaces the air in a controlled fashion as the range hood sucks it out. This is a pretty complex area and can also get very costly. There is no real regulation on this yet but authorities have set cfm limits that can be used in certain areas – typically very low at that – this is very frustrating for a ventilation person because we must match the cfm to the cooking equipment and if we can’t get enough cfm our whole effort at kitchen ventilation will be futile.More ventilation terminology- British Thermal Units – this is a measure of the heat output of the cooking appliances.Canopy – The decorative exterior of the system – sometimes referred to as a shell and can also be a wooden or stone canopy – see liner below



Duct or Ducting – The pipework that the collected is expelled throughExternal Blower - A blower unit that is mounted on the outside of the home.


Inline blower – a blower that is installed between the range hood and the outside – typically in the duct run

Liner or Insert - A non decorative range hood that is installed into the underside of a decorative wooden canopyInternal Blower – A blower that is inside the range hood canopy.

You may also hear of a term static pressure – very basically this is like horse power but the measuring and applying it gets pretty complex and is therefore mostly ignored.

Standard range hoods are available in widths of 24, 30, 36, 42, and 48 inches. For normal cooking needs, select a size that will as a minimum match or closely approximate the area taken up by the burners. (With high-performance cooking equipment, the manufacturer may recommend some overlap, perhaps 3 inches or more on each side.)

In deciding how powerful a fan you will need in the range hood, consider three things: the amount of cooking, the type of cooking generally done in the kitchen and the power(know as btu - British thermal unit - a measure of energy for gas or watts for electric) delivered by the cook top. The more frying and steaming that is likely to occur, the higher the cfm (cubic feet of air per minute) you will want handled. Fortunately the ventilation industry has developed a rule of thumb for cfm required - 1cfm for every 100btu's of cook top output - this can be calculated, by looking up in the owner’s manual for your particular cook top, the given btu's of each burner/cooking spot and add them ALL together - this presupposes the worst case ventilation scenario - all burners are on at the same time and running on the highest setting.

Finally we have a relatively new term –

BTU

How high should the range hood be installed

What height do you need?

Determining the proper height for your rangehood is a simple matter as long as you know the height of your ceiling.  Let say for example that your ceilings are 9ft high, that’s 108 inches.  You would then take the total 108 inches and deduct 36 inches for the height of your range leaving you 72 inches.  Then you will need to determine how high you would like your range hood off of your cooktop.  Modern-Aire recommends hanging your vent hood 30-34 inches above the cooking surface for optimal performance, so let’s just say that you have decided to hang it 33 inches above the cooking surface. You have 72 inches remaining, so deduct the 33 inches for the distance between your cooking surface and the bottom of your range hood and you now have a total hood height of 39 inches.

What is so special about our range hoods

We have been challenged in the past as to why our range hoods are so expensive. This blog explains why our range hoods are superior to most other kitchen hoods in the market:

1.     We use the highest grade of stainless steel and other metals such as copper for all of our range hoods

1.     Stainless steel comes in various grades - we use 304 which will not develop rust streaks over time - these are thin lines of rust that push through because there is a high percentage of iron in the stainless steel

2.     A simple test to check if your range hood is premium stainless or has a high iron content is to place a magnet on the hood - if it sticks then it is not 304

2.     Our copper range hoods for instance are made from solid copper - we do not use a thin sheet of copper applied over steel

3.     Most of our range hoods are supplied with 304 series dishwasher safe baffle filters - these unlike typical aluminum mesh filters are near indestructible and will never require replacing

1.     Baffle filters also do a far better job of capturing contaminants at higher speed

2.     These filters are typically quieter than mesh filters and will not choke under excessive smoke and steam conditions.

4.     We offer the option of mesh filters and even these are made from 304 stainless steel casing that covers the entire surface of the filter.

5.     During the construction of the hood we use whats called double wall construction  - this ensures that the hood body is rigid and will not flex or vibrate which contributes to a noisy hood fan

6.     The lighting systems on the range hoods are 120v halogen floods as distinct from low voltage lighting - the use of low voltage lighting introduces a transformer into the electrics which typical stay connected 24/7 resulting in a high failure rate of these transformers

7.     The blower and lighting controls are solid state rheostat which enables the user to have very precise control of the setting on both the blower and lights. This means that the lights and blower can be "dialed" up to the exact intensity required - there is no plastic or switching parts that can fail or become encrusted with grease. The knobs on these controls are also solid metal.

8.     Every hood is made by hand - we do not use a robotic production line as we focus our attention on the finished product and the desired look of the hood

9.     The blowers  are top of the line and considered one of the quietest and most reliable in the world

10.   We do not compromise quality - our focus is on making the best range hood from top of the line materials and we therefore do not attempt to compete on price

Hopefully the above provides a brief insight into why our hoods rank as one of the best manufactured range hoods in the world.

Questions and Answers

Here are some of the typical questions we get on kitchen range hoods and kitchen ventilation in general:
Q.
How often should i clean my filters
 
A.
We always recomend weekly or at least every two weeks. Why so often - well the purpose of the range hood filters is to collect the grease and solid contaminents in the vapor from the cook top. It therefore makes sense that regular cleaning will stop these contaminents from congealing on the filters. Most filters are dishwasher safe. Another tip is to ensure that the filters are "dried off" before re-installing them otherwise water will drip down onto the cooking surface or worse still if the fan is powered up before they are dry it could suck water up into the motor.
 
Q.
How wide should the hood fan or range hood be
 
A.
Ideally the hood should be 6" wider for a wall mount hood. For an island mount hood it is advisable to make the island deeper than the cook top as well - say 27" instead of 24". Earlier we discussed how vapor expands as it rises - thats why we recomend wider. Islands in particular are exposed to cross drafts and this further contributes to the challenge of capturing all those rising vapors.
 
Q.
Are baffle filters better than mesh filters
 
A.
In our opinion yes. Baffle filters are more effective, because of their unique design at capturing the smoke and steam than mesh filters and they are generally quieter than mesh filters. Quieter is really only an issue with high powered fans where we always try to minimize the noise of airflow. They are also more expensive!!!
 
Q.
Why do you need a range hood
 
A.
Cooking creates vapor that is laden with grease, moisture and of course some pretty powerful odors. Without an effective range hood those odors and grease laden vapor will drift through the home and attach to fabrics and surfaces. Allied to this is our homes have become extremely air tight - we dont have our windows and doors open anymore because of the AC or heating system - so all of these bad vapors get absorbed into the fabric, carpeting and onto the solid surfaces.
 
Q.
How Powerful should the exhaust blower be for my range hood?

A.
Typically the manufacturer of the cooking appliance specifies how powerful and how high the range hood should be above the stove. In the absence of this information call the stove supplier or you can use the industry rule of thumb as a guideline - 1cfm of range hood power for every 100btu of cook top output. This formula takes the maximum btu output of the cooktop - assuming the worst case scenario that all burners (gas) are on at the same time. So for example a 60 000btu gas stove top would need about 600cfm. Electric or induction cook tops are a little different - the rule of thumb here is 100cfm for every 10" of cook top - so a 30" electric cook top would need say 300cfm minimum. There are of course other factors involved not the least of which is the ducting. At Custom Range Hoods we offer hoods in 400cfm, 600cfm, 1000cfm and 1400cfm or multiples of these - yes sometimes 1400cfm is not enough - we recently completed a project with a 10' wide hood and 2400cfm external blowers.

Q.
How big should the ductwork be for the range hood

A.
Firstly one should size the duct as a minimum for the cfm that the blower is exhausting. Secondly one must factor in how many bends and how long is the duct run - it makes sense that a 200ft duct run of 6" will be less effective than a 20ft duct run of 6". Bends in ductwork seriously degrade the efficiency of the duct run - for example rather use two 45 degree bends slightly spaced than one 90 degree bend. Finally factor in whether an internal or external blower system is being used - external blowers are more efficient than internal blowers by about 20% - its easier to pull the heavy vapor laden air through the duct than to push it. Now there is as far as we know no scientific formulas or wizadry involved here. So you are now totally confused right - the answer is always oversize the ducting when in doubt - thats all we do - 600cfm = minimum 6" duct ideally 8"; 1000cfm = minimum 8" and 10" would be nice, over 1000cfm minimum 10" duct - or equivalents in rectangular ducting. If you have a really bad duct run and no other way to do it - go with and external blower.

Q.
How high should the range hood be above the cook top?

A.
The hood manufacturers specify this distance in their installation instructions.Code in most provinces or states specify a minimum of 30" distance to a combustible surface - we always advice our clients to set the hood at a minimum of 30" = if the filters get laden with grease because the filters haven't been cleaned for a year - that in our opinion constitutes a combustible surface. No jokes aside - 30" minimum is a convenient height and 34" maximum. Of interest to consider that for every 30" that vapor rises it expands outwards 3" - so if the hood is set at 60", which is totally ineffective, the vapors would have expanded outwards at least 6" in all directions - so the hood would in this case have to be 12" wider than the cooktop

How much cfm do you need for your cooking equipment

What type of ventilation is required for your coking equipment? In order to determine the proper amount of air flow required for your cooking equipment, you must first know how many BTU’s (British thermal units) your gas range emits. Then, with a simple calculation you can determine the amount of CFM (cubic feet per minute) required to properly exhaust your cooktop. For example if your cooktop emits 90,000 BTU’s you would divide 90,000 BTU’s ÷ 100 = 900 CFM. This means that 900 CFM or more would efficiently exhaust your range. For electric and induction cooktops choose a blower with a minimum of 200 CFM per 12 inches of cooktop width. Remember, it’s always a good idea to round up versus down.