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Gravity system with Circulator, New boiler, Higher bills

DaveDave Member Posts: 3

My heating system is a 2 pipe gravity setup with a circulator & Cast iron radiators.
My boiler was 30 plus years old and I was told by 3 heating contractors that at best it was 60% efficient. Approx 180,000 BTU.

I picked up a scratch and dent Burnham series 2 #204 boiler, $2000 installed.
The contractor who did the install did not install a bypass pipe, and I understand that maybe one of the issues at hand. One of my cities best HVAC companies did the install.

This is an on demand system and the boiler rarely gets up to 100 Deg. F.
I expected my therms used, per heating degree day, to go down, but they went up.
I read in Dan's Book "How Come" that I should reduce my pipe size to ¾”, but I also read in the Q&A forum where contractors are calling that a big mistake.
The piping coming from the boiler is 1-1/4” and quickly changes to the original 2” runs.

There is more than enough heat, this is not an issue.
However we cannot use a programmable thermostat as the system over shoots the temp by 5 degrees or so when we call to increase the temp, not comfortable.
I have been told that we are holding too much water in the piping, roughly 50 feet of 2” pipe, and that is where some of our efficiency is going.

I am planning on installing a bypass at the boiler to keep the temperature within the boiler at a higher level. But with this really increase my efficiency?
We are also going to install thermostatically controlled valves on the upper floor. I am remodeling this floor and building the walls out to 6” with thermo pane windows, plenty of heat.
But what should I do about the piping; do I leave it alone or change it?
If I change the 2” runs, to say 1” copper, how do I handle the ports that feed the radiators?

I work with piping for a living, just not HVAC, but I get contractor pricing, so switching to copper does not scare me.
If the suggesting is to switch to thermostatically controlled valves though out, and run constant circulation, doesn’t that defeat the bypass piping? And doesn’t that dead head the pump?

Am I missing anything?
Thanks in advance for your reply


  • JackRJackR Member Posts: 125

    You definitely need a boiler by-pass at the very least,it sounds like the root of your problem is to much flow through the boiler. The old gravity systems liked to move very slowly, adding a pump such as a taco 007 moves to much water to quickly, the old B&G 100 series circs are great for these applications. The boiler is also more than likely condensing to beat the band, a boiler by-pass is a must to say the least.

    You could also consider something like a 4-way mix valve to both protect the boiler and reset your water temperature.

    Any Mod/Con would have been a perfect fit.
  • Mike T., Swampeast MOMike T., Swampeast MO Member Posts: 6,928

    2" sounds rather small for the mains of a gravity system unless the horizontal runs are quite short--I've even seen 2" branches to large radiators on the ground floor near the boiler. Is the 50' of horizontal main in two separate and distinct supply/return pairs? If not, such sizing sounds similar to what I've seen in early standing iron systems designed for forced circulation. If a multi-floor home are the branches to the lowest (and particularly closest to the boiler) floor larger than the upper? If not, it is certainly not a gravity system.

    Regardless I would suggest that you look into a thermostatic bypass valve type ESBE. It will allow your conventional boiler to come up to it's most efficent operating temperature and "bleed" the proper amount of energy into the system. Upon observation, one of the men I most respect here once called the operation of the ESBE "almost magical". In a way it gives you the benefits of primary/secondary piping without the additional expense of another circulator.
  • DaveDave Member Posts: 3
    Gravity system with Circulator, New boiler, Higher bills

    The ESBE looks very interesting.
    Would you recommend supply side or return side mounting?
    Do I need to worry about the volume of water I have keeping the ESBE valve too cool?
    Would you mount the bypass on the boiler side of the circulator or before?

    The 2" piping is defiantly distinctly return and supply.
    The house is over 100 years old and has gone thru many updates.

    A water supply line in the attic.
    Coal room with a few coal chunks left over.
    Natural gas lighting throughout the house, that was a surprise the first time we removed an existing light fixture.
    Buss bar type wiring with ceramic guides.
  • DaveDave Member Posts: 3
    Gravity system with Circulator, New boiler, Higher bills


    Bypass on the boiler side of the circulator?

    I forgot to mention I have a B&G 100 pump that I purchased new for my old boiler. My plan was to mount it on this system. It just seams like a better pump.

    You did not mention the piping, Does this mean I should leave it alone?
  • Mike T., Swampeast MOMike T., Swampeast MO Member Posts: 6,928

    Supply mounted so that it diverts the supply through the boiler (directly into the boiler return) until it hits about 140F and then proportionally directs the "extra" into the supply to the radiators. The supply to the emitters may well never approach 140F, but your conventional boiler will be operating in the "sweet" range where it is supposedly most efficient.

    Only one pair of 2" mains? Again, that sounds rather small for a gravity system.
  • tim smithtim smith Member Posts: 2,226
    2\" may not be too small if the house is not very large

    I do see some 2" gravity systems in houses up to about 2500 sft or so, I do agree that most of the gravity systems are 2.5 to 3" supply and returns with 2 each leaving boiler. Side note, on an old low flow system like this, it might be a good app for Taco I valve w/ boiler protection ( i think they have built into it). That way he can still run system at low temps alot of the time but keep boiler in non condensing range. I like a full 4 way w/ motor better but $$ add up for this. Just a thought.
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