Reply To: Tankless Water Heaters

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From a reader who’s not registered:
““I don’t have a tankless water heater but considered getting one after a bathroom renovation and did a lot of research on them. One of the things that will affect the heater’s ability to heat cold water is the amount of BTUs that the unit operates on. The greater the temperature differential (the difference between the tempearature of the ground water and the hot water temperature you are looking for) and the water flow (the gpm of hot water you desire – the more people, fancy bath fixtures, etc., the more gpms you want) the more BTUs are needed to heat the water. When I had a plumber affiliated with a tankless heater company come to look at my place to see what I could install (this was a free visit) I was told that based upon the BTUs being supplied by my gas line I could only get a relatively low capacity (low gpm) unit because of the limited amount of BTUs left after accounting for other gas-powered appliances in my house – which in my case was only the hot water heater and the furnace. I believe you can have your gas line upgraded to supply more BTUs but you have to pay for it and it’s not cheap. A high BTU unit would have operated perfectly fine on my low capacity line until Winter whn my furnace kicked in regularly. At that point the BTUs available to heat the water would drop significantly, causing the unit to be ineffective. This BTU issue may be the cause of the complaints you’ve heard about poor tankless water heater performance in winter. I believe that if you check on Washington Gas’ website, there is some way to determine the total number of BTUs being supplied to your house. Come to think of it, the information may even be on your gas meter. You can look up the average temperature of ground water for this region to get a sense of how much it will have to be heated. Download and study the installation manuals and spec sheets for any unit you consider. All the info you need to make a smart choice will be there. Good luck.”