Gravity feed system

Mike T., Swampeast MO

Do you really have two "zones"? It's VERY common for gravity systems to use two pairs of supply/return mains, but each of those pairs typically serves multiple floors and various rooms that don't really arrange as logical "zones".

When a gravity system is converted to forced flow, the two supply and return main pairs are brought together into a single pipe using a simple rule of thumb: 1/2 the largest pipe size minus one pipe size. For instance with 3" mains you use 1 1/4" for the common piping.

A SINGLE circulator is then added to the common piping. Taco 007 and B&G 100 are very commonly used.

With two 007s driving a converted gravity system you're moving LOTS of water. So much water that you may well be hearing velocity noise! Unless this is a mansion on the Vanderbilt scale, a single 007 is likely MUCH more than adequate and is certainly moving MUCH more water than flowed under gravity.

Sorry to keep bringing up the subject, but thermostatic radiator valves (TRVs) are to iron radiators what ice cream is a warm apple pie.

Greg McLeskey

Gravity feed system

When i bought my house (built in 1916) it had an open gravity feed gas boiler heating system. I converted it to a closed system because I needed the space on the third floor where the expansion tank was located. I added a compression tank, relief valve and pressure reducing valve. Everything worked just fine. I was considering relocating a radiator and was concerned that the reconfiguration would impact the effectiveness of the gravity feed system so I added two circulator pumps(there are two zones). The professionals with whom I consulted at the time suggested I use Taco 007 pumps placed on the return lines. They also suggested that I let the pumps run continuously so I did not use any sort of device to control the pumps. The pumps were too noisy for my taste from the beginning and they have gotten louder over time. It is hard to compete with the silence of gravity feed. My boiler is over 30 years old. It has a huge standing pilot and no damper. I am just about convinced that I should remove the circulators and enjoy the peace and quiet of gravity feed, but I don't want to lose any energy savings the pumps might contribute. I am sure that replacing the boiler or at least converting the standing pilot and adding a damper would give me greater energy savings than the pumps. So, my question is, should I worry about the loss of energy savings(whatever that may be) I will incur if I remove the pumps? Where do I get a boiler with two inlets/outlets to replace my current boiler or should I just convert the pilot and add a damper to my existing boiler.

If you got this far, thanks for your time.

Greg

jeff_51

pumps shouldn't be making ANY noise

something is going on here. Either vibration noise, or air or something. Depending on your piping configuration, most of us here would pump from the supply, but your piping configuration may make that more difficult. Can't of course tell without looking at it. No reason to have two supply and return tappings off of a new boiler. You would take care of that with new near boiler piping. You probably have 2 or even three inch heating lines, those would be downsized to 1 1/4 or maybe even 1 inch depending on boiler size and btu's needed in each zone. Get rid of the old beast

Constantin

I agree...

Gravity systems are notorious for being over-pumped. I would take a very close look at the pumps vs. the flow requirements with an excellent tool like Siggy's HDS program to see what kinds of velocities you are likely to develop. Chances are, that with two big pumps, like the 007s, the water will be zinging through the system, with the resultant very low ΔT's at the rads, flow noises, etc.

Mike's suggestion of TRVs on rads is a very good one. It obviates the need for individual electronic zone controllers and substitutes KISS units in their place that allow you to microzone until the cows come home.

Anthony Menafro

Trv's

With TRV's you would have to make sure of a bypass if the system is not looped independantly anywhere. I also think that to move the volume of water in an old gravity system, a #100 series or a Taco #0010 would move more water more effectively while allowing the rads to absorb the BTU's they need to put out. This would allow the last rad on the line to have enough water moving through it to remain even tempered with the other rads.

Anthony Menafro

Greg McLeskey

I was hearing velocity noise at first. I spoke with Taco and they suggested I shave some material off of the impellers. I removed material incrementally and by the time the velocity noise was gone I had removed a significant (50% perhaps) of the impellers. The noise at this point is a slight high pitched whine with a loud low pitch waaa waaa resonance.