Determining size of existing heat pump

I recently bought a house with a Lennox heat pump, about 18 years old. Model HP19-411-3P. I have the sticker from the HP unit & the installation, operation & maintenance instructions. I've also looked at all the labels/wiring diagrams on the inside of the unit's cover. Nowhere in any of this is the tonnage of the unit mentioned. I can tell you it is charged wih 11lbs 3 oz of R22. Can anyone tell me the tonnage size of this unit, or where I can find it? The Lennox site anly had the manuals I already have. Don't think it matters, but the other components are heating element unit ECB19-15-1Y & air handler CB19-41-1P.
TIA
Dan
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I'd call a local Lenox dealer and give them the info or try customer service on their website for help. JAT

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My guess is 3.5 tons.

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