We have a Heatilator GNDC30 direct-vent fireplace unit in our house. It's wired for a blower unit, but the builder didn't install it (which is pretty common). Instead of paying someone to come out and stick one in, I decided to order the blower itself and give it a shot.
The blower I got was a non-OEM replacement for the manufacturer's FK21 fan kit. I'm sure that the OEM kit has a bracket that holds the fan in place under the fire box, but this one did not. It really only needs to sit under the firebox and shoot air up the back
Th e blower itself is just a small squirrel cage with an AC motor and a variable motor control. The motor is a little too heavy, so it leans to one side if you don't hold it in place. During test-fitting I noticed that not only does it lean to one side, but that the opening of the fan is larger than the slot that carries air up the back of the firebox. I made a little box out of sheet aluminum and stuffed a roll of non-slip in the middle to give me a cutom-sized vibration-reducing block to hold the motor level. The difference in duct sizing causes a lot of wind noise even at low speeds. To remedy this, I made a little duct flap out of sheet aluminum to point the air appropriately. Here are the pieces. And the final result with the flap installed in the blower housing.
To further reduce noise and vibration, I cut another piece of non-slip to set the whole thing on once it's in-place. I would tend to bet that the stock unit just mounts to the sheet metal and thus could potentially rattle.
Next, I just slid the whole thing into place in the back of the firebox, and put the little support box under the motor.
It's a little hackish (okay, maybe a lot hackish), but it is a retrofit. Hopefully tonight we can test it out and see if it makes a difference in heating the living room 