We are thinking of replacing our current natural gas tank water heater by a high efficiency tank less heater.
However we have a water main issue, the house is from 1930 and the main is partially clogged. We had people from the town water service and a local contractor who does water main replacement come to our house and long story short we have no short term solution to solve the main clogging issue. Anyway, because of that we have good water pressure but low flow. Meaning as long as we only one faucet opened water pressure is great but it drops as soon as we open a second one.
I read several posts online about people complaining of pressure issues with tank less heaters but it seems to usually be because of undersized units for their house. In our case we have only one bathroom and are already use to not using 2 faucets at the same time so I don't think this would be an issue. We are looking at a 9 GPM rated unit.
Now my question (sorry for the long introduction): Not considering the sizing question, do people observe a water pressure drop when installing a tank-less unit compared to a similar flow rated tank unit? I'm not sure how a tank unit works. Does it refill at the same time as you are using the hot water or is the refilling process asynchronous? I'm afraid that the tank less unit would actually behave like if we had 2 faucets opened at the same time...sorry if the question is stupid or doesn't make sense.
I will obviously also ask his opinion to our plumber but I like to get different opinions.