HVAC tech and I (and architect) are looking at the needed dimensions for the triangular space inside the attic 'pony wall' (5 ft high at the top of the triangle of the pony wall is current design; unit is 21"X40"X30" wxhxd) in order to put in a 5 ton horizontal forced air gas furnace. Length is no problem, but we're struggling with how much clearance from the pitched roof to the air handler/coil there needs to be? Tech wants more clearance, architect is trying to squeeze as much floor space out of this attic buildout as possible. We're in Houston--comments on code would be appreciated as well. Thanks.
How much clearance? As much as possible. Remember, the architect doesn't have to work on that unit, otherwise he'd see things differently.The manufacturor will state minimum clearances in their specs, but if you squeeze it in there you'll be sorry later on, as you'll be charged out the kazoo to work on it. JMO
Tell arch to turn 180 degrees, then kick him in butt....!
Knee wall spaces are about the worst to put a unit in without sheetrock, they're really bad to replace a unit in.
Don't put any structural stuff directly in front of the unit! You'll just have to cut it out later. Since you're looking to save floor space you won't be climbing in a closet crawling in front of unit, sounds like doors will be attached to wall to take off and gain access directly.
So you're looking at measuring up from floor the installed height(includes drain pan and supports) to the rafter plus a few inches to play with(put mark on floor). Measure horizontally out the depth of furnace or drain pan (the deeper one) plus a few inches. This will be the back side of wall.
Remember- access to repair, access to replace, without being a contorsionist or tearing the house down.
Did I mention the shoe leather enema?
thanks so much for the comments, points taken. Manufacturer's clearances for the coil and furnace, and the space created by these 5 foot pony walls--along with ~ 44" width of access door (probabably a double door) for direct access should be adequate.
I say build a mock up with some old lumber laying around. Then when you see how cramped it is, find another location to install the unit.