Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
(OP)
If a mechanical engineer says "oh, and we need your help to support three 10 ton RTUs", what number does your brain start to think of in regards to self weight of the RTU? (On a current project the mechanical equipment schedule shows that a 10 ton roof top unit has an operating weight of 1300 lbs).
This would be nice to know in the future when in those field conversations with mechanical engineers. I thought I came across a rule of thumb that: X-tons heating/cooling equates to a range of Y to Z lbs of operating weight. Does anyone know of any general rules of thumb on this?
Thanks
This would be nice to know in the future when in those field conversations with mechanical engineers. I thought I came across a rule of thumb that: X-tons heating/cooling equates to a range of Y to Z lbs of operating weight. Does anyone know of any general rules of thumb on this?
Thanks






RE: Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
RE: Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
I did see all of the new grads, hired after me, return to their desks panic stricken as to how they could support that much weight on their roofs. The mechanical designers thought it was funny.
gjc
RE: Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
Jayro12 - point well taken regarding the aluminum vs. steel swapping to save weight.
RE: Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
One thing to look for is the snow drift when the unit gets to be over 15' wide.
RE: Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
3 ton- 600 lbs
5 ton- 700 lbs (skid size: 80"x45")
6 ton- 700 lbs
7.5 ton- 960 lbs
15 ton- 2300 lbs (skid size: 92"x 125")
On the ones where I give the skid size, if you work that out.....it comes to about 26-29 lbs/ft2.
I don't know if all that gives you any rule of thumb. JLNJ's number (above) looks pretty good to me.
By the way, these units include the compressors which (I think) makes them heavier than chill water units (for big buildings).
RE: Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
RE: Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
Dik
RE: Rule of Thumb for Roof Top Unit Weights based on Heating/Cooling Tonnage?
And, a quick aside: yes, in these conversations with Mech Engs, I always try to educate them on the 15-foot threshold for snow loads. They're not used to taking suggestions from SEs, however, when I inform them that a unit slightly bigger than 15' may result in an additional $5K, $10K, $30K, cost to the Building Owner to reinforce the structure because of drift requirements, some of them appear to take note.