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# Door Opening Force Calculation - Staircase Pressurization

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## Door Opening Force Calculation - Staircase Pressurization

(OP)
Hi All,

I'm unable to figure out a "PARAMETER" in Door Opening force Calculation. I have the formula from ASHRAE and I can substitute values to find the answer. No problem in it. But there comes a parameter that I could NOT relate where it exactly appears on doors. The measurement "DISTANCE FROM DOOR KNOB TO KNOB SIDE OF THE DOOR" is the one. I was wondering from where to where do I need to measure physically on a door. ASHRAE also suggests that while calculating I can take this value to be 75mm. I'm done with the calculation. I'm trying to justify the assumption of 75mm.

Is it between the knob and the latch that gets engaged into the wall?

Would anyone please help me out to figure it out?

Thanks in advance for the help!

### RE: Door Opening Force Calculation - Staircase Pressurization

The way the phrase is written, it's the distance of the outside most point of the knob relative to the door surface it's mounted on.

TTFN (ta ta for now)
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### RE: Door Opening Force Calculation - Staircase Pressurization

It would be the distance from the center of the knob to the nearest edge of the door. 75 mm is pretty standard for door locks.

### RE: Door Opening Force Calculation - Staircase Pressurization

75mm being slightly less than 3 inches would mean, as stated above. the edge thru which the latch is penetrating.

### RE: Door Opening Force Calculation - Staircase Pressurization

"KNOB SIDE OF THE DOOR" is pretty clear. That makes the measurement perpendicular to the face of the door.

The backset, which is the distance from the center of the knob stem to the latch to the edge of the door, is typically 2 3/8" or 2 3/4"

TTFN (ta ta for now)
I can do absolutely anything. I'm an expert! https://www.youtube.com/watch?v=BKorP55Aqvg
FAQ731-376: Eng-Tips.com Forum Policies forum1529: Translation Assistance for Engineers Entire Forum list http://www.eng-tips.com/forumlist.cfm

### RE: Door Opening Force Calculation - Staircase Pressurization

Say F1 = force to open door (pull at door knob)without door closer
Equating moments about door hinge:

F1 x (W-d) = P x A x (W/2)

P = Pressure on door on lb/SF = (in wg x 62.34 lb/cu Ft water)/(12 in/ft) = 5.2 x in wg of water

F1 = (5.2 x in wg of water x A x W)/(2 x (W-d))

where A = SF door area
where W = ft door width
where d = ft distance from center of door knob to the edge of the door nearest the knob.

With door closer total force F to open door in lb

F = F1 + Fdc

where Fdc = lb force to overcome door closer

### RE: Door Opening Force Calculation - Staircase Pressurization

(OP)

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