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Replacing Tank Water Heaters with Tankless

  • Transcript

    LESLIE: Lazlo in New York has a question about tankless water heaters. What can we do for you?

    LAZLO: Yes, hi. I happen to have two tanked water heaters. It’s for a four-family building.

    TOM: OK.

    LAZLO: And it basically has – I think the two of them are 50 gallons each.

    TOM: Mm-hmm.

    LAZLO: And what I was thinking of doing is minimizing the actual heat on those two tanked water heaters and putting in an additional tankless water heater after the two tanks. So this way that the temperature would be, say, something around 80 degrees in the tank water heaters and then when the demand comes on then the tankless would heat it up to the 105, I guess, or 110 degrees so that somebody can take a shower or, you know, do the dishes or whatever it is that they need the hot water for. I was wondering if that’s a good idea or not.

    TOM: Are the water heaters that you have gas or electric?

    LAZLO: Gas. I’m going to be using gas for both the tankless and the tank.

    TOM: It’s a bad idea. Because you don’t need to preheat the water. If you have a properly-sized tankless water heater then you absolutely don’t need to preheat the water and, in fact, doing so would ruin the efficiency of this equation. So I would tell you that if you want to go tankless – I think it’s a good idea if your water heaters are getting to be old – put in the right size tankless water heater and eliminate the other two 80-gallon water heaters because they’re going to waste a whole lot of gas that you don’t need.

    LAZLO: OK. They’re actually 40 or 50 gallons …

    TOM: Alright, well …

    LAZLO: … but I see what you’re saying. Either way. Right.

    TOM: Same point.

    LAZLO: Yeah, yeah.

    TOM: Yeah. No, you don’t need to preheat the water into a tankless. Tankless water heaters are engineered to take the water from, you know, ground temperature cold to 110, 120 degrees on one shot and they do that endlessly if they’re properly sized and properly installed. When you have the plumber come in to install it, make sure that they look very carefully at the manufacturer’s specifications for gas line size. Very common mistake they put in too small of a gas line. Tankless water heaters need a large gas line because they use a lot of gas but they use it for a short period of time and, overall, they’re much less expensive to run than a traditional tanked water heater.

    LAZLO: Right, right, right. That’s why I was thinking of going with that. OK. Sounds good. They actually – they are getting on in age, so I would probably have to replace them in about a year or two anyway.

    TOM: Smart to do a preemptive strike here, Lazlo, and to replace them before those tanked water heaters start to leak because that’s a big mess.

    LAZLO: I thank you for your help.

    TOM: You’re welcome. Thanks so much for calling us at 888-MONEY-PIT. 

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