I'm afraid your information needs may be beyond the knowledge of participants on this forum. You might ask over on the HVAC Forum to get specifics you need. In general though, a louvered door will provide the combustion air for your furnace and water heater. You might want to get the BTU information from both appliances before posting over there. Good Luck.

The open leg table gives unrestricted air to your systems return. You do not want to compromise the operation of your unit. I think even 6" would be to close. That is a mechanical area. The way to test it is to read the static pressure on the return side of the furnace. Let's say everything is properly sized and installed. With a magnahelic gauge or digital manometer you could read the static pressure on the return. Then move the heavier piece into place and read it again. If the static pressure increases you have restricted the air flow. I think your table looks great there;)

Could be the ductwork is detached in the attic and the air coming into the conditioned space is only being drawn in by the outgoing return air. Could be other causes involved. But the fact that you posted here without looking first (apparently) indicates the need for a competent technician on site.

I found a local dealer willing to sell me the sight glass (it's actually Pyrex) and a matching gasket for about 20 bucks. Although there were lower prces out there, most shops sell only to those licensed in the trade. Oh the irony. The burner tech who caused the damage has agreed to cover the cost of the parts - as long as I install them. We'll see if he pays as promised when they arrive next week. mr.havac... I asked the burner tech to downsize the nozzle to save a bit on fuel. I made extensive improvements to the ductwork layout and tripled the ceiling insulation when the furnace went in. Since then, I have suspected that the system was just a bit oversized. I'll know for sure this winter! BTW...I've earned the right to be a royal PITA. Do you remember when I installed that furnace almost two years ago? The oil tank, fuel line, fill/vent piping, flue pipe, and nealy all of the ductwork got replaced, as well. The plenums were bent and cut according to scale plans I drew up. I ran new 12/2 through a new heat fuse and wired it. I even added a vent alarm (the oil deliveryman appreciated that one). I pulled a mechanical permit - signed by the town building inspector (cost of permit - 20 bucks, peace-of-mind - priceless). Everything is to code. This was a soup-to-nuts DIY install. All of this work is no big deal to someone who does this for a living. However, it's a helluva big deal to me. So yeah I'm picky. I didn't spend all that time and money doing it right only to have a PAID professional screw it up. The sight glass is right over the gun with a crack going down the middle. I can easily feel the crack, as the glass on one side of it is now higher then the other. So the crack is really a split - held together with two screws by the bezel and gasket. There's no doubt that the glass will come out in two pieces when the assembly is removed. Would you allow a furnace to run like this over a season? Would you charge a customer 100 bucks for this kind of work?? miken_2008... The furnace is a Crown CLBR 68-112. BTW...mr.havac is right about the link in your sig; It shouldn't be there. Peace. Marco