Tank or tankless water heater for 3-family home?

After finishing extensive renovations to the owner’s duplex, we’ve realized we need to upgrade the water heating system for the entire building. The water’s currently heated via an old oil boiler, which isn’t the ideal situation in the summer or when the two rental apartments are occupied (which will be starting May 1st!). We’ve spoken to several plumbers about installing either a gas-fired tank system (A.O. Smith 75 gallon) or a tankless (Navien NPE-180), and there seem to be tradeoffs involved in either. For the time being– due to budget overruns on the earlier renovation– we’re keeping the oil boiler, though we may look to do a conversion in the fall. Would love to get people’s thoughts on the better option here…

If we went with the tank, we’d install a leak tray underneath and a leak shutoff sensor. It would be vented through the chimney, next to the other vent for the oil boiler.

If we went tankless, it would have to be vented outside, so we’d have PVC piping running up along the exterior wall. We already have a small backyard, so we wouldn’t necessarily want to reduce the space further.

Whatever option we went with would need to be sufficient to produce adequate hot water for a 3-family home (3 dishwashers, 1 washing machine), for about 5 people.

Guest User | 4 years and 3 months ago

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Guest User | 4 years and 3 months ago

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Thanks for the advice, Bob and UrbanDad– I knew we’d need a high-efficity/high-gallon-per-minute model if we went tankless, but I still had concerns (though it was initially suggested by a chimney guy who was cleaning out the existing oil vent, who said we wouldn’t have to vent it up through the chimney). For installing a new water heater of any sort, I’m assuming we’d need to file a permit, correct? I’m asking that because I’ve gotten somewhat conflicting answers from different plumbers!

hkapstein | 4 years and 3 months ago

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A tankless produces water on demand so it must use a huge amount of fuel to meet peak demand. The advantage is there is no standby loss and no running out or hot water. But the heat must be designed to produce enough btu to meet the peak demand of the building. If someone fills a washing machine for 30 seconds, you don’t want the showers getting cold. In a one family home where people know how much they can use, this might be okay, but what’s the point of having 3 bathrooms if only one person can take a shower, or if filling a tub would prevent any other faucet from getting hot water? Probably the gas line will need to be upgraded. For a 3 family I think I’d prefer the buffering of a tank. If tenants take a cold shower because you’re doing laundry or filling the tub, they won’t like it, so your system will need to be large. Tankless heaters I think require more maintenance and are more like to cause headaches like cold water sandwich that you and your tenants won’t like. But they have there place. An individual tankless in a small 1bdrm apt might make sense, separately m etered and would take up less space than a tank heater. That’s my 2 cents. A tankless may do the job if it’s sized right and the building usage doesn’t exceed it peak capacity, but a tank is probably a safer choice.

RobertGMarvin

in General Discussion 4 years and 3 months ago

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There have been numerous threads about the inadequacy of the tankless systems