Techniques for getting air to the 3rd floor

[khanegan]

I am a new homeowner without too much knowledge of home repair. My wife is currently 7 months pregnant and the room we would like to use in on the third floor of our town house...We have central air conditioning, but it was put in after the house was built. As a result, the heating fan is too small for pushing the air conditioned air up to the 3rd floor. We closed all the vents in the 1st floor, but it still does not get too cold upstairs. Rather than purchasing a bigger fan and motor for the unit, does anyone know any alternatives?
I have heard there is some kind of fan you can place on the vents that will suck the cold air up through the ducts into the room but I cannot find them anywhere...does anyone know what this is?
Thanks for any help
//kevin h

[metalhd2]

Kevin h,

What you are referring to are called in-line booster fans. You
should be able to find them at any Lowe's/Home Depot. You will
need to know the pipe/flex duct diameter because the fan and the
duct need to match in size. The upside is they are fairly simple
to install requiring a simple junction into the house current for
power. The downside is they are limited in effectiveness. While
every application is different I have never found them to be 100%
satisfactory. Having said that, they are a simple, low cost solution.

Ed/metalhd2