Most engineering specifications for smoke testing identify the use of a blower able to provide 1750 cfm (cubic feet of air per minute), however in today’s world it seems to be the mindset that bigger is better. New smoke blowers on the market can deliver well over 4000 cfm, but is this really needed? Once the manhole area is filled, the smoke only needs to travel sections of generally 8 or 10-inch pipe. Moving the air very quickly is useless if the blower does not have the static pressure to push that air/smoke through the lines. If you’ve used high cfm blowers and found that smoke frequently backs up to the surface, this may be your problem. Keep in mind that high cfm blowers have a higher air to smoke ratio which reduces the density and consequently the visibility of the test smoke. Therefore, while a high cfm blower (with appropriate static pressure) may have more “reach,” it does not necessarily provide a better smoke test. In general we have found approximately 1800 cfm to be ideal for most mainline sewer tests. There are situations however where a higher output is beneficial. Systems with limited manhole access that necessitate smoke testing long stretches of line at a time and/or systems using very large diameter pipe may benefit from a higher cfm blower.