This is an OT reply. I really mean it, Off Topic, way out in Left Field.
You don't have to read this if you have blood pressure problems. Honest.

If one lives in Suburban Mid-West, your home and the land that your home is
on is most likely yours. If a DIY really messes up with NG, Propane,
Venting, CO poising, then only the family involved is, well, ah, involved.

But in many major cities, NYC in this thread, a home owner is just as likely
to be a "Condo" owner. That is really an apartment building that was
converted into a "Condo". Yes, the owner's home is his' / her's / their's
but the potential is more than one home is involved if the DIYer screws up.
A natural gas fire in one home will just as likely affect more than one
other Condo home.

NYC is NOT known though out Western Civilization as having too few lawyers,
nor having a population reluctant to phone a lawyer with little or no cause.

The issues of a high density population living in a very high cost of living
environment creates issues of municipal oversight that is
incomprehensionable to many of my neighbor in suburban Detroit. And I only
lived in Baltimore, which was a lot lower population density than a some of
the Boroughs of NYC.

Simple example: the chimney that a Hot Water Tank vents to. Is this chimney
dedicated to that home only? Is it a converted fireplace chimney? Is
there a problem with the "cold air column" of an outside wall chimney during
winter? If the water tank's T&P valve pops, is the drainage water going to
affect any other home owner in the Condo?

If the OP was living out on Long Island in one of them Levittown places, I
would very much encourage him to DIY the hot water tank. He will need the
knowledge and the confidence building from doing so for later in life
projects.

(This is just IMHO, from my experience in Baltimore) But if He is living in
a condo situation inside NYC-- There is a risk (outside chance) a neighbor
might call a lawyer to demand that the installation be halted, and wait for
a licensed plumber and inspector to do the installation correctly before
the gas burner could be turned on... well that is a risk in lawyer packed
NYC. Plus, and this could be worse, I think the neighbor just might be
able to force the OP to pay for the Lawyer on top of going without hot water
when his wife returns.

Anyway just my OT opinions. Anyone may ignore my rant if you choose.
Now if you will excuse me, I need to find some plate steel for my butt when
the flaming starts.

Phil