After working in water supply and drainage for one year, I want to take the postgraduate entrance examination for HVAC, learn plumbing, and then go to the construction unit. Is there a future?

I have worked in a design institute for a short time, less than 4 years. Water supply and drainage and HVAC in our hospital are all done together. Personally, I think water supply and drainage is more difficult than HVAC. Since I entered the design institute, I don't have to take the postgraduate entrance examination. Now the design institute is not so easy to enter, there is no need to go to the postgraduate entrance examination and then change the construction unit. Personally, I think the design institute is more promising. Why not register? It is more important to register after the exam. Now the registered teacher of plumbing is still very valuable.