How do you determine the tonnage of commercial rooftop HVAC units?

I’ve gotten the advice:

  • Divide the last two (of 4) numbers of the model number by 12;
  • Use 1.4 x the compressor amperage;
  • Calculate it using the BTUs somehow;

…and then there’s the date of manufacture:

Carrier said that they encode their commercial HVAC the same way they encode their residential HVAC, so the Building Intelligence center will work for that, at least for carrier. I don’[t know about all the others. Anybody???

Contact the manufacturer.

Any suggestions?

Just guess and hope you don’t get sued? :joy:

I think that works best if you wear a mask during the inspection, get paid in cash, and put your closest competitor’s name on the agreement.

Oooop. I just found something saying that it’s 1 ton per 12,000 BTUs.

There are some manufacturers that encode readily intuitive tonnage or BTUs into their model numbers, but some don’t do anything intuitive, like Mammoth. Mitsubishi VRF City Multi’s also come to mind. Not readily intuitive, but the size is there if you know what to look for. You really have to build your own library. One thing I’ve done over my career is collect O&M’s for everything weird I’ve ever seen, like the old Sterling units that had refrigeration coils, or low boy induction units, or electric boilers, or the old Marley cooling tower O&Ms. I’d say once a month that library comes in handy.

I must admit, I had to do a search to find out what an O&M manual was. Then I searched “Carrier O&M manuals” thinking I could start building my library. Turns out they have almost 12,000 of them.

But this is a good time to mention to newer inspectors that building a library is an important part of building your business. Your browser Bookmarks is a good friend. Build an organized library of technical articles, manufacturer’s installation recommendations, message board posts, and anything else that might be helpful. I haven’t saved O&Ms but I have saved the rest and use them often.

If they are visible the thermal expansion valves have the size on them,many larger units have more than one,in which case add them up and be pretty close to the tonnage.