Can you recommend an engineer or architect that can conduct this work?

My architect is giving me really hard time on this and I have seen many ADUs with tankless water heater but I just dont have their contact.

These companies still have to hire an architect or an engineer to stamp drawings. 

Even very good architects/developers cannot possibly understand all the different nuisances of a trade.

A couple of things that someone might learn, was when you go to the zoning board have an architect draw you up a few pictures.

@Kevin Lefeuvre will always depend on your architect and engineer. 1-2 months can be an average expectation from request to submitting for plan approval 

I'm looking at a building this week that needs to have a full site plan done as we plan on doing a change of use from fully commercial to mixed us. I was wondering if anyone can recommend someone?  The building is in ...

I worked with Kinecta Credit Union, Architect, Contractor.

I paid an architect to come out in a situation like this and they weighed in on whether it was likely to be compliant or not.  

Those are the cheapest instead of having an architect do everything from scratch, even those will add some cost to your Soft Cost budget since the plans don't cover any of the permit cost associated with them.6) Keep in mind that you will need 20-25% cash to secure the construction loan for this project, some banks may let you use the debt free land as a portion of the collateral on the deal to get you to that 20-25% target to secure the construction loan.