DHW - Terminology Questions...

PFloro · January 11

I do understand what "indirect DHW" means.

But...

If a boiler has a tankless coil and no external holding tank, what is this type of DHW called?

If the above boiler has a holding tank connected to the tankless coil (but no heat exchanger in the holding tank), is a different term used...?

I'm trying to learn in preparation for buying a house in Weschester County, NY next summer.

Thanks for your expertise. I have already learned so much from this site...!

Paul

EBEBRATT-Ed · January 12

If the boiler has just a coil in it it is called a "Tankless Coil". Usually on oil boilers only. Tankless coils do not have a ton of DHW capacity and are considered less efficient because the boiler must be kept hot year round

2. A storage tank attached to a boiler where the circulator pumps boiler water through a coil inside a tank is an :indirect DHW tank or just indirect.

3. A storage tank above the boiler is less common although used on older installations.

It consists of a storage tank (like an indirect) with a coil in it or a insertable coil called a "tank heater" was used. The tank was placed above the boiler so the boiler water would circulate to it by gravity although they could also be pumped.

4. There is also an "Aqua Booster) which is a tank that contains DHW. These tanks use the Tankless coil in the boiler and the circ pump circulated potable water. They are sometimes added to a tankless coil boiler when it won't produce enough DHW.

The indirect tank is the most common now to heat DHW froma boiler

Hope I didn't confuse you

hot_rod · January 12

yet another option is an insulated storage tank with an external plate heat exchanger. Energy Kinetics promotes this method with a thermal purge function when the boiler shuts down.

Plate heat exchangers are about the most efficient way to generate hot water, related to two pumped counter flows.

PFloro · January 12

Thank you both... ...and you didn't confuse me...!

40 years ago, I had experience with an oil fired steam boiler (1950s era) with a tankless coil. It was full of minerals and didn't produce much hot water. When the boiler leaked, we went to a 40 gallon natural gas water heater. The new gas boiler was a Weil-Mclain EG-35. Since I wanted basement heat, I configured the boiler with a tankless coil to use with 30' of fin tube baseboard convectors. That basement loop with all the necessary hydronic bits worked perfectly and independently for the 20 years we lived in that NJ Cape Cod (steam upstairs & hot water in the basement)...!

Paul

EdTheHeaterMan · January 12

A New Jersey Cape Cod, I think that sounds like a geographical oxymoron.

I like the Indirect for four reasons

Recovery as you are using the DHW. That burner is big enough to heat your whole home. When dedicated to heating potable water you have a big burner making more hot water than you can use thru the shower head. Other burners are sometimes less than ½ of the size of the space heating burner.
The tank is not connected to a vent of any type. So there is no heat loss up the chimney or out the vent.
Down time storage lasts longer. If you are not using hot water for the entire day while you are at work, chances are the water heater will not call for the burner to operate. Other water heaters can call for recovery every 4 hours even if no hot water is used during that time.
The vented source heating boiler can go to room temperature within an hour or two after the tank is satisfied. No call for heat in the summer and no call for hot water if not is used for many many hours.

DHW - Terminology Questions...

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