I’ve been reading through a few threads on here. For larger installs it often seems to be quoted that a design engineer would be required.
When I suggest it, it is normally due to the reason
@Riley gave, meaning that someone sounds 'out of their depth'. Plumbing and Heating is quite often a subject that lay persons have little understanding of, yet seem to think that they can buy over-sized equipment, pipe it together and all will be fine, particularly on more of the private light Commercial systems.
Thus seems a little alien to me, I’d expect a spark to be competent enough with basic design principals for a care home. How come this seems to be something done by a third party in the heating sector?
In my experience it isn't. We design, spec and install all our own work. As Heating Engineers that's an important part of our job as you would expect.
Larger companies do tend to work with a Commercial Heating consultant and design team along with pipe fitters, electrical Engineers, Gas Engineers (other fuels of course), Plumbers etc etc. You would come across those in say, a new build School, Hotel, Hospital etc. This is due to the size of contract.
Commercial Plumbing, Heating and Hot water systems can be a lot more complicated than people realize. It takes many years to become a competent Heating Engineer and to enter into all the whys and wherefores about the subject on a Forum is practically impossible. Sometimes it gets to the point where you think the enquirer would be better served paying for an Engineers experience and advice as opposed to plundering on in the semi-darkness and reading various differing opinions on a forum.
A little knowledge is dangerous!
