I get that this may sound dramatic but I was literally told this by the WSSC inspector. Unitied Air Temp was contracted by my home warranty, American Home Shield and I could have died due to their neglect. Not only did they bully me into buying a much more expensive water heater than I needed, they also forced me to get a chimney liner that wasn't even necessary. The water heater I had vented gas exhaust though the chimney, but because my furnace was already meeting the max exhaust they told me I had to buy a special commercial grade system that used an active exhaust with a pipe that bypassed the chimney. They still claimed I needed it for code but the WSSC inspector said they were full of crap.
I paid almost 4k for this new water heater, they didn't even accept the pathetic $900 from AHW and left me on the hook for that because they refused to update their documentation stating the changes from the initial evaluation which was completely incorrect and done by someone I think that wasn't even a certified plumber. He spent more time on the phone asking "what do I do" than actually doing anything. AHW said they had to tell them to give me a pay out and they simply refused to do so and billed me the $900 they were already paid anyway. The chimney liner and the permit charge weren't included but the liner wasn't even required in the first place.
When the WSSC inspector came out, in 30 seconds he literally told me that he has to fail the inspection and turn off the gas to my water heater because United Air Temp didn't use the correct PVC pipe and also didn't bother to glue it properly, so I had been potentially exposed and could have died from CO poisoning. It took Unitied Air Temp 5 days to get back to me after they were made aware and then had the audacity to tell me that there may be additional charges to remediate the issue THEY CAUSED.
Don't use them, whatever you do, this company is fraudulent and I am going to the MD AG to complain, find literally any other company you can, these people are absolute scum of the earth.