What is ACH and Why It is Important?

Are you planning to buy an air purifier and is not quite clear about some of the technical parameters associated with air purifiers like ACH, CFM, CADR etc? If so, you have come to the right place.

This article will explain what is meant by the term ACH and why it is important in the context of air purifiers.

What is ACH and How it is Calculated?

ACH stands for Air Changes per Hour. The ACH rating is a measure that tells how many times per hour an air purifier device can exchange the air within a room. More fresh air exchange means better air quality in general.

ACH ratings provides information about the number of times an air purifier can filter the air in a room each hour.

For instance, an air purifier with an ACH rating of 3 means that it will purify the air throughout the entire room up to 3 times every hour.

Ideal ACH values for different spaces are calculated and specified by scientists. So different ACH valued are recommended for different spaces like bedrooms, kitchens etc.

The formula for calculating ACH for a space is given by the formula, ACH=CFM*60/Area*Height.

Thus ACH depends on the volume of the room/space and the CFM (CFM stands for cubic feet per minute, it’s a unit used to measure how quickly air flows through a purifier)value of air purifiers.

Why is ACH Important for Air Purifiers

The ACH value is important for air purifiers as it helps us to determine whether an air purifier with a specific CFM value is suitable for a specific type of room/space.

Experts and scientists recommend ACH values for different types of spaces and we can calculate the ACH for an air purifier if we know its CFM value and the volume of the space we plan to use the purifier in.

For example, it is generally accepted that an ACH between 5-6 is adequate for bedrooms.

With this information we can decide a particular air purifier with a specific CFM value is suitable for a bedroom of certain dimensions.

Assume that the area of the room is 200 square feet and height is 10 feet. Then the volume of the room is 2000 cubic feet. Let us assume that the air purifier in consideration have a CFM of 300

Now applying the formula ACH=CFM*60/Area*Height, we get: ACH=300*60/200*10=9

Since the ACH is greater than the recommended value the purifier in question is suitable for the room.

Further, it is clear that for this particular room purifiers with a CFM between 167 and 200 is the minimum requirement.

What are Ideal ACH guidelines for various spaces?

As mentioned before ideal ACH values vary across different types of spaces.

These values are recommended by scientists and experts after considering various factors.

The table below gives information about recommended ACH values for a variety of settings/spaces.

Table: ACH for various Buildings / Rooms

Type	ACH value
Assembly halls	4 to 6
Attic spaces for cooling	12 to 15
Auditoriums	8 to 15
Bakeries	20 to 30
Banks	4 to 10
Barber Shops	6 to 10
Bars	20 to 30
Beauty Shops	6 to 10
Bed Rooms	2 to 4
Boiler rooms	15 to 20
Bowling Alleys	10 to 15
Cafeterias	12 to 15
Churches	8 to 15
Classrooms	6 to 20
Club rooms	12
Clubhouses	20 to 30
Cocktail Lounges	20 to 30
Computer Rooms	15 to 20
Court Houses	4 to 10
Dance halls	6 to 9
Dental Centers	8 to 12
Department Stores	6 to 10
Dining Halls	12 to 15
Dining rooms (restaurants)	12
Dress Shops	6 to 10
Drug Shops	6 to 10
Engine rooms	4 to 6
Factory buildings, ordinary	2 to 4
Factory buildings, with fumes or moisture	10 to 15
Fire Stations	4 to 10
Foundries	15 to 20
Galvanizing plants	20 to 30
Garages repair	20 to 30
Garages storage	4 to 6
Homes, night cooling	10 to 18
Hospital rooms	4 to 6
Jewelry shops	6 to 10
Kitchens	15 to 60
Laundries	10 to 15
Libraries, public	4
Living rooms	3 to 6
Lunch Rooms	12 to 15
Luncheonettes	12 to 15
Nightclubs	20 to 30
Machine shops	6 to 12
Malls	6 to 10
Medical Centers	8 to 12
Medical Clinics	8 to 12
Medical Offices	8 to 12
Mills, paper	15 to 20
Mills, textile general buildings	4
Mills, textile dye houses	15 to 20
Municipal Buildings	4 to 10
Museums	12 to 15
Offices, public	3
Offices, private	4
Paint shops	10 to 15
Paper mills	15 to 20
Photo dark rooms	10 to 15
Pig houses	6 to 10
Police Stations	4 to 10
Post Offices	4 to 10
Poultry houses	6 to 10
Precision Manufacturing	10 to 50
Pump rooms	5
Railroad shops	4
Residences	1 to 2
Restaurants	8 to 12
Retail	6 to 10
School Classrooms	4 to 12
Shoe Shops	6 to 10
Shopping Centers	6 to 10
Shops, machine	5
Shops, paint	15 to 20
Shops, woodworking	5
Substation, electric	5 to 10
Supermarkets	4 to 10
Swimming pools	20 to 30
Textile mills	4
Textile mills dye houses	15 to 20
Toilets	6 to 10
Town Halls	4 to 10
Taverns	20 to 30
Theaters	8 to 15
Transformer rooms	10 to 30
Turbine rooms, electric	5 to 10
Warehouses	2
Waiting rooms, public	4
Warehouses	6 to 30
Wood to working shops	8

Should You Choose Air Purifiers with High CADR?

CADR stands for Clean Air Delivery Rate. CADR rating indicates how fast the air purifier can clean the air within a particular size room. A purifier with a higher CADR means that it can purify air faster.

While high CADR is good measure generally, it should not be the only consideration.

Higher CADR value can improve ACH also and so generally while choosing an air purifier it should be ensured that the CADR of the device will satisfy the minimum recommended ACH value for the space in which it will be used.

FAQs

Summary

We hope that this article has helped you in creating a clear picture of ACH, its meaning, importance, and uses. If you have further queries or doubts regarding ACH, please mention them in the comments section.

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