I really do understand what you mean with your ideas for ventilation, and for the home gardener who wants to have something less expensive and is satisfied with the life span of the the items, it's a perfect solution.
However, the fans like the Tjernlund M series, which is all stainless steel, and will last 10-20 years of 24 hours per/day, 7 days a week, 365 days a year, the less expensive ones don't stand a chance against them.
Something like the Lasko will last about two years if you're lucky. It's real good for a way to move air, but if the restriction of ducting is added, it's life will be shortened remarkably from the strain put on it's motor.
Fans are pretty much nothing more than blades, motors and bearings. They each have expected lifetimes under certain conditions. With a fan such as the Lasko, the motor is expected and built to have no strain from any ducting or restrictions. When those are added, the life of the motor will lessen.
Bearings have a range of quality and lifespans a mile long. During my time as an Industrial Mechanic, I dealt with thousands of bearings. Bearing failure is predictable in most applications.
The costs come down remarkably with some products because their lifespans are very limited by the parts used in their manufacturing.
I would risk to say that with only 6 feet of ducting added to the Lasko you linked to, it would live about a year...maybe.
I understand and have seen some "Saturday Night Rigging" in my 58 years. The ingenuity and imagination of some people just impresses the hell outta me.
But when dealing with my own Return On Investment, I'll stick with items that are made to deal with the use I intend to give them.
My $130 Tjernlund will outlive your Lasko by at least 500% and as much as 1000+%. It's cost is only 260% of the Lasko.
Another consideration is home insurance. If my Tjernlund has catastrophic failure and somehow caused a house fire, it is being used exactly as it is intended to be used. If the jury-rigged Lasko was used with ducting attached and caused your home to burn down, your insurance carrier would laugh and walk away with the money.
I always keep catastrophic failure in mind in reference to home insurance. I have some friends who are firemen, and they tell me of some things they've seen jury-rigged in houses that they have put fires out in. Their stories scare the heck outta me and make me use things that are made for what I use them for.
It's a calculated risk if you jury-rig things. The "What-Ifs" come into play.
I do understand where you're coming from however. For hobby use, I would probably do what you're suggesting. Fan failure wouldn't really be much of a problem that way.
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