These are my thoughts BEFORE the event later today.This is the event that basically reveals the "how" Tesla will continue to grow their dominance in the EV industry.1)  Million mile battery -  a battery that will last longer than any ICE (old school fossil fuel burning combustion engine) car.   2)  New battery technology (code name Roadrunner)- higher density, cheaper manufacturing cost, newer cheaper/environmentally friendly ingredients =  translation:  lower cost of the making the car and easier manufacturing to further their mission.

They need combustion air to operate (unless it's a newer high-efficiency furnace with its own intake air pipe coming from outside the house). 

Presumably, a lot of it is combustible.

Couldn't a spark from from a reciprocating saw or angle grinder cause the oil or fumes to combust, even if most of it is out of the tank?

Combustion air system needs to be added as well.

Disclaimer: I am not a professional plumber.If it's an electric water heater, this doesn't apply.If it's a gas water heater... do you have a sufficient supply of combustion air to the closet you made?

Modern gas stoves and fireplace inserts are sealed (airtight) with respect to the living space (room) and vent their combustion air from outside - typically a separate pipe through the side of the building or a centre pipe within the exhaust flue (either through the side of the building or as a sleeve in an existing chimney.The cheapest way to stop air and heat from being drawn up your chimney is to decommission your fireplace; stuff insulation in the top of the firebox against the closed damper; then tape a sheet of 6mil poly (vapour barrier) under the insulation being certain to create a seal with the sides of the firebox all the way around the perimeter of the barrier.Since you still want to use your fireplace periodically, but do not wish to incur the expense of installing an airtight insert, you could still attempt to plug the top of the firebox when you are not using the fireplace.  

StanleyAny system that uses combustion as a means to heat anything poses an un-necessary risk...regardless of circumstance or cause any failure, diminished performance, or catastrophic failure with heating equipment ( stove, oven, furnace, water heater ) can have devastating consequences As a former public safety official I would never have any devices that use combustion as a means of heating anything especially as a landlord Best wishes for your continued successBob

Optimists like to point to growing services and seeds of tech startups but the economy is still primarily dependent on producing vehicles that utilize the combustion engine.

Rethinking Transportation 2020-2030: The Disruption of Transportation and the Collapse of the Internal-Combustion Vehicle and Oil Industries (RethinkX Sector Disruption) (Volume 1) 1st Edition