Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Tankless water heater

I'm impressed with the tankless water heater, but must say that if I had know what I know now about the installation I would have thought twice about purchasing it. My old water heater vented with 3" vent. This unit take 5" and above 2000 ft elevation you must vent with 6". I'm just under 4000 ft. So you must install new vent up through the roof. The unit uses more gas, but for a much shorter time, so it must have 3/4 inch gas pipe plumbed to it. All in all quite a bit of work, but I'm sure it will pay for itself in the long run. I did all the labor, if someone had to pay a plumber to install the product it would be a much longer time before it would pay for itself!