Which is better for cooling a large room?

The B20201. It is rated at 1820 CFM, and the 3733 has no published airflow figure. Both are 20-inch box fans, so placement near a window matters more than the model.

Which one lasts longer?

Hard to say from specs alone. The B20201 has a 1-year limited warranty and a much larger pool of owner ratings; the 3733 lists no warranty. Both use a steel body and the same 7.25 lb frame.

Is the B20201 worth stepping up to over the 3733?

Yes for most shoppers. You get a published airflow rating, a fused plug, a carry handle and far more owner feedback for the same fan size and weight.

Are they the same size?

Yes. Both are 20-inch box fans weighing 7.25 lb with three speeds and a 6-foot cord. The B20201 stands about 22 inches tall.

Can either be used in a window?

Yes. Both are free-standing 20-inch box fans that fit typical window openings. The B20201's slip-resistant feet help it stay put on a sill.

Box fans of this type are noticeable on high and quiet on low. Neither model lists a decibel rating, so expect typical box-fan noise at the top speed.

Lasko 3733 20" Box Fan vs Lasko B20201 20-Inch Box Fan

Both are 20-inch Lasko box fans with three speeds and a steel body, so the choice comes down to airflow and track record. The B20201 moves a rated 1820 CFM and has thousands of owner ratings behind it; the 3733 has a much smaller rating base and no published airflow figure. Buy the B20201 for a bedroom, garage or workshop where you want strong, proven airflow. Buy the 3733 only if you want the same basic fan in a lighter-duty package.

Choose the Lasko 3733 if you want a simple 20-inch three-speed box fan and don't need a published airflow rating.
Choose the Lasko B20201 if you want proven airflow, a long track record with owners and a built-in carry handle.

Prices

Lasko 3733 20" Box Fan: $24.95 at eBay (last seen Nov 8)
Lasko B20201 20-Inch Box Fan: $24.95 at eBay (last seen Nov 8)
Difference: both cost the same at the latest prices (Nov 8)