Buffer Tank Piping Buffer

Buffer Tank - A Different Idea

All the piping diagrams on this website are simplified and does not include any devices required for actual installation. Please apply standard installation practices.

For decades buffer tanks were piped using the four tapings, two for the boiler and two for the system. Recently that is starting to change. Instead of using all four tapings now there are many jobs using two, three or all four tapings. You also may not want to maintain temperature in the tank but let it heat as it would on zone demands. If you pipe a two or three pipe tank application I usually would not maintain the tank temperature dependent on the application. This allows the use of a buffer tank for an alternate system temperature instead of using a mixing valve. For instance, if you have a high temperature system and a small radiant load the tank could maintain the lower temperature for the radiant in the tank and eliminate the mixing valve. The advantage to this would be no moving parts See drawing on bottom of this page. On a four-pipe application I would consider maintaining the temperature in the tank. When you apply a buffer tank to a system be aware of how to pipe the IWH into the system.

4-Pipe Connections
Buffer tanks normally have four pipe tapings, two designated to the system and two designated to the boiler flow.

2-Pipe Connections
Here is a thought, you use only two of the buffer tank tapings and pipe the system supply and return pipes to the boiler supply and return pipes. Why, you will get heat quicker to the heating system and save fuel by not maintaining tank temperature as some do. When doing this it is important to keep the supply tees close to the tank tapings to create hydraulic separation between the tank and will include the tees.

3-Pipe Connections
Another idea is using a 3-pipe application. This will keep the boiler running with cooler water temperature longer and the boiler efficiency will be higher. When applying a buffer tank to a high efficiency boiler or air-to-water heat pump this is my go-to piping choice.

Flow in a buffer tank
This is what happens when the flow in the system is lower than the flow through the boiler. Notice the boiler water goes directly to the zone but some water passes through the tank, cooling off the return water causing the boiler to run at a higher efficiency.

When another zone opens in this example the flow to the system is equal to the required flow in the system and no water flows through the tank.

Next when all the system zones are in demand the system flow rate will exceed the boiler flow rate. As you can see by the text showing GPM flow in purple, the water temperataure is lower than the boiler supply temperature. We will be adding some cooler return temperature through the tank, but as the supply temperature increases the return temperature increases. Another advantage is most of the heating season your demand will not be all the zones so the tank temperature will be storing hotter water than cold start.

While we are thinking out of the box here is another way of using buffer tanks

Another scenario is there is some low temperature radiant in a home that also has high temperature heating like copper tube baseboard and/or hydro-air. The radiant could be added to the system with an aquastat to limit the tank to maybe 120f. We would not want the radiant supply pipe before the tank like the examples above because the water would be to hot to the low temperature radiant. Use all four tapings on the tank, two for the boiler loop and two to the radiant heat loop(s).
Using this application all the radiant on the tank would have to be able to heat properly using the same water temperature. Being able to set the tank temperature on using the tank aquastat there would not be a reason to do any mixing on the radiant. I would just use the aquastat as a limit control to a maximum setting for the application of the radiant heat. The setting would be dependent on the radiant heat application. Wire the aquastat in series between the zone control for the radiant and the boiler demand terminals. Most high efficiency boilers today have more than one heat input terminals and some even allow multiple temperature outputs. If not, just piggyback the single heat demand terminals. Do not piggyback on DHW terminals as we do not want this on priority. If you do not have an IWH you could use the DHW terminals but make sure you turn priority off. Applying this piping as any other zone it is critical to size the circulator properly for the radiant buffer tank. Of course, as any piping application you may have to change the piping slightly. Do not This may also require a pump setting change on the pump parameter.

Disclaimer: The information found on this website is for informational purposes only. All preventive maintenance, service, installations should be reviewed on a per job situation. Any work performed on your heating system should be performed by qualified and experienced personnel only. Comfort-Calc or its personnel accepts no responsibility for improper information, application, damage to property or bodily injury from applied information found on this website.