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eeprof
"Makeup" or return air.

In this day of tightly sealed structures with very little air infiltration I pose the following question: Bathroom exhaust fans are typically rated at 100 cfm while some large kitchen vent hoods are rated as high as 800 cfm. Central vacuum systems also "suck" on the house envelope but are not rated in cfm. Where are these devices supposed to get their "makeup" or return air in a well designed structure?? They can move any air if there is none available. Thanks in advance.

canuk
Re: "Makeup" or return air.

Yep ...you are right on the money.
The exhaust systems as well as central vacs do create issues and without proper make up air can cause problems with negative pressure in the home. This can cause a problem where combustion devices compete with air inside the home and may affect chimney drafting..

In this area it's mandatory to have a source for fresh outside to be used as make up air. Many instances Heat Recovery Ventilators (HRV) will used for this purpose.

http://healthandenergy.com/heat_recovery_ventilators.htm

There is also the benifit of exchanging inside air to improve air quality.

JEWEATHER
Re: "Makeup" or return air.

As Canuk said, you are right. If you don't have an air intake source, these exhaust vents will sure find one, and if that means pulling air back down a chimney or flue pipe, that can spell trouble. New houses in my area are required to have a fresh air intake from outside. The HVAC contractor runs a vent from the outside into the return air duct of the forced air furnace/AC unit. I would imagine that other areas are beginning to impliment similar codes as well.

eeprof
Re: "Makeup" or return air.
canuk wrote:

Yep ...you are right on the money.
The exhaust systems as well as central vacs do create issues and without proper make up air can cause problems with negative pressure in the home. This can cause a problem where combustion devices compete with air inside the home and may affect chimney drafting..

In this area it's mandatory to have a source for fresh outside to be used as make up air. Many instances Heat Recovery Ventilators (HRV) will used for this purpose.

http://healthandenergy.com/heat_recovery_ventilators.htm

There is also the benifit of exchanging inside air to improve air quality.

My geographic area is extreme south Georgia which has mostly cooling days rather than heating. It is also rural with numerous tree growth that produce pollen. If I were to install a fresh air intake it would admit pollen laiden, high humidity 95 degree makeup air. These conditions accentuate the makeup air problem. I need the opposite of heat recovery!

canuk
Re: "Makeup" or return air.

Well to be honest the term Heat Recovery Ventilator had been commonly used for quite sometime mainly because these types of units were widely used in colder climates.

However .... aside from the name they actually work with A/C as well by tranfering the cooled air inside the home to the warm incoming air .... precooling if you like ...... you just have to expand the thought.

It's becoming more accepted to refer to these units as Energy Recovery Ventilators ( ERV).

Everyone of these devices have some sort of incoming air filter system incorporated. Some are more finer than others ... for example this company uses a Merv 12 filter
http://www.ultimateair.com/Ultimate_Air/recoupaerator_intro.aspx

JLMCDANIEL
Re: "Makeup" or return air.

Regardless of what they are called the units use an air to air heat exchanger which transfers heat from the hot air to the cool air regardless of the direction. Add a blower and a proper filtration system and you get the fancy name. And by the way a central vacuum system, unless the vacuum unit is mounted outside of the house, causes a zero loss of air in the structure.
Jack

canuk
Re: "Makeup" or return air.
Quote:

Regardless of what they are called the units use an air to air heat exchanger which transfers heat from the hot air to the cool air regardless of the direction. Add a blower and a proper filtration system and you get the fancy name

Geez ... Jack that simplies the basic operation alright. The main component is the heat exchanger ..... not to be confused with straight air exchange.;)

Yep .... I should have qualified my comment about central vacs .... they absolutely do remove air from the living space if they are exhausted outside .... the unit can still be indoors.

bsum1
Re: "Makeup" or return air.
Quote:

Yep .... I should have qualified my comment about central vacs .... they absolutely do remove air from the living space if they are exhausted outside .... the unit can still be indoors.

Ah, that clears it up. I was going to say the same thing as Jack.

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