I bought an m-6 and an m-8. The m-8 is better balanced and seems less noisy than the m-6. Both are still impressive overall. Longevity and tolerance to overheating are untested at this point. Update: After further observation, I can see that the m-6 was dropped or subject to a similar hard impact prior to arrival, perhaps in the factory, perhaps by Amazon. I'd say that is why its legs are bent, and probably why it is louder, slightly unbalanced, and sounds like a bearing has issues. At first, I thought the bent legs were part of the design, because both were evenly bent, but the m-8 has straight legs, is well balanced, and runs quietly... lesson learned. Had I bought only one, I would have just thought that's how they all are, ha!

WORKS GREAT

WARNING FIRST: This ships with a cardboard collar inserted on the intake side. It was VERY wedged in there on my fan. So much so that I wasn't sure if it was a piece left over from the manufacturing process that got missed. It was reference NOWHERE in the instructions or on line. I had to wait until the next day to reach them and ask about it. Turns out I would have done no harm in TUGGING on it to get it out. So all ended well after all. But if you are considering buying, just know that so you don't lose a day.

ON TO THE FAN:

This is an excellent fan. I installed it to go through a rim joist to vent a corner of my basement into the space under the front porch. So final picture: Outside the house is the metal outlet cover and its end-cap with the flappy bit to keep bugs out when the fan is off (purchased separately). I pushed it through the hole and into my basement. That gave me about a foot inside of the 16 inches or so of ducting attached to the cap. I slipped the fan over it and screwed the fan to the side of the nearest floor joist. That set up sucked a LOT of air. But it was pretty loud. So I decided I would live with it, but then went on to testing the bits of ducting and flapper valves and what-not on the intake end of it (since it was there!) just to get an idea of how things fit (intake is smaller than outlet). And lo and behold! I grabbed a piece of 4" duct splice (just an 8-inch long piece of ducting made to splice 2 normal lengths/diameters together) and slipped it on. It was a bit of a loose fit, but some blue painter's tape made for an adequate seal (ability to undo is greater than aesthetics up in a back corner of my basement!).

Now for the kicker: That little 8" piece of duct made all the difference in the world to the sound! It had a huge muffler effect. I'm guessing the loudness of the original sound really was about the sound of the air being beaten around by the internal impellers. This reduced it to mostly just the sound of air rushing in. I probably cut the noise in half or better. So tip to ya!

Very good fan. I use it to pull air from my basement and pass it around my sealed combustion fireplace to heat the house more efficiently (removed the weak 150 cfm squirrel cage fan that came with the fireplace). I also created a damper "by-pass" so I can easily reverse the air flow and heat my basement using the same duct system without having to flip the fan around (BTW, the fan is not electrically reversible). Air flow/suction is excellent. Noise level is acceptable if insulated kevlar flex ducts are used (metal ducts transfer noise more readily). I have a speed control installed, but I seldom use it as I like to have the fan on high to utilize its full potential (that's why I purchased the 6" fan versus the 4" fan).

This is my second M-6 fan ( the first one had an impeller problem). The first fan developed the same "wobble noise" as another buyer stated. I had the fan installed for a couple years when it developed the problem. I took the housing off and noted the fan/impeller blades were attached to the "cage" with full plastic on one side and plastic "studs" on the other attached to a metal crown. The small studs (made of plastic melded onto the metal crown) appeared not to be properly anchored and allowed one of the plastic blades to eventually bend and push against the fan housing causing the wobble/noise problem. I tried to straighten the blade and re-anchor it to the cage. So far so good (about 1 year in with the fix) There is a noticeable, but slight, vibration probably from an out-of-balance situation. I just purchased another Tjernlund M-6 fan from Amazon (of course the price was great and free shipping). I looked into the impeller and it appears the entire unit (blades and cage) are all plastic which will eliminate the "plastic stud" separation problem I had. Maybe the company had a problem with the original design and corrected it. My original unit is still functional and is destined to become a garage exhaust fan.

Anyway, for less than $90 this fan performs very well even when utilizing several elbows in the line. According to the manufacturer it can handle air temperatures of up to 140 degrees F. I pushed 130 degrees through the unit for hours day-after-day with no problems to the motor, housing, or bearings.

Bought a 240cfm in line and it was hardly noticeable at the register. It's a 2nd floor room and the air hanlder is in the basement. Replaced it with this guy and...WOW! It's moving more air than I need. Happily bought the speed controller to get that oh so sweet perfection!