Q: Jason, I have a Majestic SR42A 42″ prefab wood-burning fireplace with gas logs.  The damper is 8″ round and opens/swivels in the middle of the circle.  The firebox is a trapezoid with approximate dimensions of 24 X 33 with the sides being 15″.

There is a front “panel” that seems to be angled inward making the 15″ sides taller at the top and smaller at the bottom. There seems to be sufficient room between the damper and the top of the fireplace opening (9″) for a larger Chimney balloon.  The front panel may also make a good “shelf” for the Chimney Balloon to rest on.
I’m wondering if the best bet is to go with a smaller Chimney Balloon and install it above the damper with the extender or get a bigger Chimney Balloon and install it under the damper, in the trapezoid firebox area.  My preference would be for easy installation and removal as we use our fireplace a lot in the winter.  I don’t mind if part of the Chimney Balloon or pole shows. – CA
A: Dear CA, You have a couple of choices in how to install your Chimney Balloon.
Option 1: If you plan on putting in the Chimney Balloon and leaving it (ie. not using this fireplace much) than I would suggest you get a 9×9 and put it above the damper with an HEK extender. This configuration will get your Chimney Balloon up and out of sight from the firebox area and it will give you a nice tight seal in the flue area.
Option 2: If you will use this gas log fireplace regularly and you are looking for the easiest place to install a Chimney Balloon to take it in and out. I would recommend you get a 36×15 Chimney Balloon and install it right in the firebox below the damper. When your damper is closed the handle will be up and out of the way and you have a nice trapezoidal spot there that is 9″ tall to put the Chimney Balloon in. The only downside is that you may be able to see the Chimney Balloon a little bit in the firebox. Also, you will want to be careful of the sharp edges on the damper handle bracket that I see in this picture that holds the damper up when it is closed. Those brackets can have a sharp edge on the tip of them so you may want to put a piece of tape over that spot so you can get maximum longevity out of your Chimney Balloon. Sharp spots like that can tend to wear out the Chimney Balloon early if you are installing and uninstalling regularly. – Jason
Afternote: This customer decided to purchase the 36×15 Chimney Balloon.