The Difference Between Condensate and Boiler Feed Tanks
I have been asked many times over, "What is the difference between a condensate receiver and a boiler feed unit". This can only be answered by explaining what each does. I will discuss the condensate receiver tank first.
Condensate Receiver Tank and Pump
A condensate receiver is a small tank, with low water volume that works remarkably similar to a sump pump. There is a float and switch assembly that operates a pump motor to pump the water into the boiler when the water level rises enough to activate the float switch. They are used when returns cannot be piped back to the boiler. or the condensate is below the bottom of the boiler. Another use is when you do not have the proper "B" dimension which is 30" per pound of pressure on the system between the lowest steam carrying main and the boiler water level. The downside of this is the pump will pump the water into the boiler whether the boiler needs the water or not. This may cause the boiler to overfill or worse. yet the boiler may go to a low water condition and the pump does not have enough water in it yet to bring the water level of the boiler to a proper operating level. The Make-up water is added into the boiler when using a condensate receiver which is not good for the boiler.
Boiler Feed unit
A boiler feed tank is much larger tank in water volume. Today most manufacturers would rather see a boiler feed tank than a condensate pump today. The boiler feed unit is operated by a pump controller mounted on boiler. The pump controller will start and stop the pump dependent on the water volume in the boiler. Instead of feeding water to the by a float operated switch. When the water level is high enough the pump controller will shut down the pump on the boiler feed tank.
In a nutshell the boiler only gets water when needed and gets as much as needed. The condensate receiver will pump water whether the boiler needs water or not. Another advantage to a boiler feed tank other than more water volume, pump controller the make-up water is fed into the boiler feed tank by a float operated switch. When the make-up water is fed into the tank the oxygen can leave the water in the tank instead of the boiler. When the oxygen is released in the boiler it causes oxygen corrosion which creates holes at the boiler water level. The second advantage to adding make-up water to the boiler feed tank is the dissolved solids drop out in the tank not in the boiler where they collect in the smaller water ways in the bottom of the boiler reducing water flow in the sections. In short a boiler feed tank will extend the life of the boiler life.
Both tanks are more common today then the prior few decades, and not restricted to very large residential or commercial applications usually around 500,000 btu's and larger.
First things first, when you decide to install a tank you eliminate the need for an "A" or "B" dimension. For more information on A & B dimension click Here. If you have a dry return you will need a trap on the return line before the tank but not right at the tank. Do not eliminate the equalizer pipe when using either tank. Even though you will not need to equalize the pressure you still need a header drip. The equalizer now becomes a drip so any condensate in the header will go down the equalizer pipe to the return of the boiler.
If the old condensate receiver or boiler feed unit is in a pit, more then likely the best choice is to probably leave it in the pit. It is probably there for proper drainage from the heating system. Over sizing is more critical with a condensate pump than with a boiler feed tank.