# HVAC Furnace hanging in attic



## Uncle Bob (Dec 6, 2012)

It's new to me.  I came across an HVAC Furnace hanging from the rafters in an attic.  Does this require engineering specifications?  Haven't found anything in the codes about hanging loads on rafters.

Thanks


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## ICE (Dec 6, 2012)

I see that a lot.

Seldom is it an engineering issue.

Two fatboys on the roof is probably as much weight as a furnace.

If it's over-spanned 2"x4" rafters with the furnace in the middle, it could be a problem.

Something to watch out for here in earthquake country is lateral bracing.


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## jar546 (Dec 6, 2012)

It is one thing if it evenly distributed and potentially quite another if is hanging by 4 threaded rods creating point loads.  PV systems add very little weight and I have seen the calculation, and the math shows the increase is negligible.  Not so sure on HVAC hanging from rafters.  It is easier to determine when it is on ceiling joists.

Great question UB!


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## globe trekker (Dec 6, 2012)

> Does this require engineering specifications?


This depends! What size is the unit, ..how is it being supported ( wires, threaded rods, wood framing,

other ?), ..is the unit also supporting additional ductwork, ..how much vibration will there be when the

unit is operating, etc. etc.. Also, does the weight of unit and all of it's associated attachments

( ductwork, piping, etc.) meet the requirements of R801.2, which directs you to Section R301 in the

IRC. Also, see Section R301.7 for deflection.

.


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## brudgers (Dec 6, 2012)

With rafters, it's pretty straight forward to figure out if it works. Except in edge cases, span charts, the weight of the unit, and an informed lay person's understanding of beams is adequate. Trusses are another matter. Then again, they usually get cut.


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## ICE (Dec 6, 2012)

One of the corrections was to install lateral bracing.


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## Uncle Bob (Dec 8, 2012)

Thanks for all the input.


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## mark handler (Dec 8, 2012)

R8Ol.2 Requirements. Roof and ceiling construction shall be capable of accommodating *all loads imposed* according to Section R801 and of transmitting the resulting loads to the supporting structural elements.

R802.10.1 Truss design 4.5. Concentrated loads and their points of application.


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## RJJ (Dec 8, 2012)

Where is the pan for that unit if it has AC. Rafters appear to be 2x4's


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