sub in the fireplace

My parents are building a new house and are putting the sub in the fireplace. Do they need a front firing sub? Should they put acoustic foam around the sub?
Two suggestions:
1. Make sure if you use acoustic foam that it is not flamable.
2. Never let Ben Stiller in your home to "Meet the Parents", he might just set a blaze to the sub/s. Sorry just saw that movie and it seems like sometihng he would do.
If they use a downward firing sub, be sure not to install it upside down. This would scare Santa and if he lands on the spikes it will surely be a bag of coal for your parents.
It's not a fireplace; it's a custom sub enclosure.
That chimney would make a helluva transmission line, wouldn't it?
Expensive Duraflame log? I think they're going to have to experiment with that one and then post the results. Elgordo - whats the best listening position for that transmission line? Would it be in the basement or on the roof? Streetman, good luck to your parents.
I thought I was the only crazy to do this. I sealed off my fireplace with expanding foam and carved out a nice shell and painted it flat black. The sub is down-firing and side ported. My firebox sits about 10" off the floor. It sounds great, and it's a great conversation piece. People look at my speakers and are in awe at how low they go. I just laugh. Plus, it hides an ugly big square box that clashes with the room. I say go for it if it works for them. Works for me.