great product and reasonable price. bought an extra one just to have as a spare

We ordered it with 2 day delivery because our furnace needed it to run.
It arrived in my view in 2 days. Except for a little tin snipping to make
it fit, the furnace was running again in a couple hours. Perfect. Thanks

It is bigger than expected , as i looked up dimensions I was looking for something to put on a 3" vent line off a hot water heater
I talked to the company that builds them and a distributer and this is what they endorsed.

I just finished installing and testing for few hours, and I thought I will write down some notes about this draft inducer. My water heater is an "orphaned water heater" (type these words in Google and you will see some sites with good info). The first picture shows the rust on the top of my water heater due to backflow that happens in windy days :o(
The inducer is well made, and comes as pictured. You will need to wire to plug in (I used an old desktop power cord). Inside the package, there is a template to be used (as a sticker) to make the appropriate cut in the duct and make the 4 holes to attach the inducer. It also contained 4 small bolts with metal clips (like those in cars called u-clips or panel clips) that go over the metal duct and has a thread to secure the screws.
The owner manual says that can be installed from 3-6 inches duct. Yet, it will not fit well for 3 inches. Mine was 3 inches, and I used a drill bit to make the starting point, and a jigsaw with a metal blade to make the cuts. Once I made the cuts, I realized that there is no way for the lateral flaps to stay over the duct without bending it (this could cause a serious leak). Also, I should have waited to make the holes until the inducer is mounted on the vent duct. The holes did not align up in this attempt.
So, I went to a closest hardware store, bought 4 inches duct and 2 pieces of adapters (3 to 4 inches). To make new cuts, got a Tjernlund specification pdf file on the web to get the size of the hole, make a simple template on paper, and restarted. Once it was mounted nicely, I made the holes, put the clips. And discover that 2 of the 4 bolts do not have clearance to use a nut or screwdriver to tighten. A bad design. I ended up using a needle plier to tighten.
Although this product description in Amazon seems to indicate that you can control the speed with Vary-Draft control, there is nothing in the box to do it. So, it is a single speed as it comes (I think there is a more expensive package that includes few other things but it's 3-4 times more expensive). You plug in and it runs. To avoid this little motor to run all the time, I bought a "Century 7 Day Heavy Duty Digital Programmable Timer - Dual Outlet" here in Amazon. It allows you to program up to 8 on-offs a day. I have programmed 3 on-offs in weekdays and on weekends in slightly different times.
The 2nd and 3rd pic shows both sides of the installation. The screws on the motor side are the ones without enough clearance for a screwdriver. The little zip ties and wire on the motor were used while I was installing the duct with the mounted draft inducer (since the weight tend to turn the duct). It allowed me to maintain the level for the motor as the user manual specifies while I was using some screws to secure the vent. The last pic is the timer that controls when the motor will be running. It is not a perfect solution, but simple enough for us that we have a regular schedule during the week with work and school. I have posted 4 pictures, so I hope that it will eventually show up.
I hope that this helps a little.

Good product