firefire-pitfireplacepatiopropane
I have a propane fire pit in the center of a table on our patio. Since the weather is still fairly chilly where we are, I was trying to think of something creative to channel the heat towards the 4 seats on each side of the square table rather than straight up in the air. Does anyone have any ideas? Thanks in advance.
The model building codes provide separation distances based upon radiant heat, construction type, occupancy, fire resistance of the exterior walls and the ratio of openings to solid wall in the building to be protected.
Keeping in mind that the fire separation distances given are in feet from the property line and that adjacent buildings have similar requirements one could use the combination of IBC [2009] table 602 and table 705.9 to determine separation. As a rule of thumb, 60' would be the maximum required between two buildings each located 30' from the property line.
However, I recommend discussing the issue with your local fire official. There may be additional considerations that limit or prohibit the use. The fire official may also be aware of additional environmental, utility infrastructure, or fire service availability factors that increase or decrease the risk associated with a large fire pit.
If you set the forest ablaze, the distance between the pit and the structure will become irrelevant.
We had a similar issue. The solution is to stack up larger chunks of lava rock into something that is vaguely pyramid shaped. As you note, the heat rises and if you have a large stack of rock over the flames, the rock will redirect this convective heat through the rock and heat up the rock itself. Once the stack of rock is heated (ours gets quite glowing red in the middle), it radiates the heat out to the sides (where people are sitting) quite effectively... much better than the flat layer of rock in the bottom of the fire pit. Since most of the heat is in the middle of the ring, that is where you want your stack tallest since it will extract more useful heat that way.
The only thing you need to be careful of is the stack of rock tumbling down. Fortunately, lava rock is quite porous and there is a lot of friction between two pieces. You can easily stack the rock in an interlocking manner and test it but pulling or pushing to ensure that the stack is stable, and that red hot rock won't come tumbling out on you while the fire is going. With heating and cooling, the rock will shift over time so it is best to inspect the stack periodically to make sure it stays stable.
Note, I'm talking about large size lava rock, not the stuff I see in your fire pit. Something like what you see here: 
Best Answer
Reflection of radiant heat is what you would be after. If you could magically hang it, one of the best would be a metal surface above the fire reflecting heat back down to everyone. Using an upside down cone or pyramid shape, with the middle point centered over the burner and the angles set so that the surfaces would reflect the fire and heat (radiant heat and the light of the fire follow the same path) right at the seating area. A hanging flat surface would go a long way too, such as a hung metal plate or even a tarp (don't start a fire). I'm not sure that this is that feasible. I don't think much else would help since the heat is mostly radiant and any that is in the form of hot air will just rise away if not in some sort of enclosed structure