Can Tankless water heater use circulating lines?

FHHO

Can circulating lines be connect to the tankless heaters?

I would like to convert to tankless, but afraid my circulating lines would become obsolete.

The reason I got the circulating lines is because I have a large home and it used to take a while for the hot water to push all the stagnat cold water out of the lines.

Uni R

Point of use...

Put a tankless near each collection of usage points and you won't have to recirculate.

Ken_8

Of course

you can. It would probably be best however to use a by-pass sort of arrangement.

Just make sure the pump is bronze - and about as small as they make.

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Scott Gregg

Tankless Recirc...Yes, but...

Yes you can but... most will have a warranty effected. Another thing to consider is that if you recirc the same way as you would a tank heater, you can (and probably will) get a burst or two of unheated water leaving the tankless between cycles. This can make your phone ring. It is known as a cold water sandwich and if you are in the shower enjoying your "instant" hot water, it is no fun when that slug of water gets to your back.

A good way to avoid this is to have a small (8-10) storage tank directly after the tankless. This way if a quart of unheated water gets out, it goes into a 8 or 10 gallon resovoir of hot water and is diluted to the point that it not noticed.

IMHO. The best way to accomplish recirc with a tankless is to come out of the tankless and into a small (10 gallon) electric water heater. Tie the recirc line into the hot main between the tankles and the tank and install chack valves to keep the flow right. Us a pump with a timer on it and an aquastat set at about 15* differential on the hot return.

With this system you by-pass the tankless and the small tank keeps the hot water main up to temperature, thereby saving the warranty and not cycling the tankless on/off. The aquastat makes sure to shut off the pump when it is up to temperature helping you not waste energy for nothing and you can set the pump's timer to shut the pump off during hours when you know you do not need it to run.

The small tanks only job in life is to maintain loop temp and it will typically only have about a 15* temp rise.

By-passing the tankless like this also lets you use a smaller head pump as most tankless have a pretty good head loss, somthing like 15', not sure exactly.

JackFre

Yes they can.

Scott's advice is very good on the use of the small storage tank. Before using a recirc however, look for alternate locations for the water heater. Closer to the point of use is better. Installation cost may be a bit higher but long term enrgy savings will be much improved and you get the best out of your on-demand unit.