adding a circulator pump to a single zone system

Discussion in 'Boiler Forum' started by rrcur, Dec 14, 2011.

  1. rrcur

    rrcur New Member

    Messages:
    14
    Location:
    Southern Maine
    I have a small, two story house with a five-year-old cast iron oil boiler that provides hot water to cast iron radiators. The piping to the radiators is fairly large diameter black iron, which may have originally been steam piping. The house was built in the late 1920s, and it's all one heating zone, controlled by one old mercury thermostat.

    At four locations in the basement, iron piping has been removed back to reducer tees. Two of these tees are in the supply pipe, and two are in the main return. I assume that a previous owner removed a couple of radiators and iron piping that used to connect to the main loop at these points.

    Currently, one pair of these tees is plugged, and the other pair has been connected to a make a ¾†copper loop that runs to a 3’ length of fin tube in the upstairs bathroom. I recently added a small hydronic kickspace heater to the return pipe of this ¾†loop using scoop tees and 1/2" copper.

    I suppose I should have expected this, but the flow through the ¾†loop at the moment is poor. The upstairs fin tube has always generated a decent amount of heat in the coldest part of winter, when the boiler is on almost constantly, but not much in the shoulder seasons.

    Is it possible to increase flow through the ¾†copper loop by adding a small circulator pump (like a Taco 006 B4) at the return end of the loop, just before the copper re-joins the black iron pipe? If so, should it be wired to the primary circulator pump (located in the main return line, just before the boiler) so it cycles on and off with the main pump? I’m concerned that if it runs independently of the main pump it won’t be effective.

    Any other suggestions? My, time, skills and budget are limited, so I won’t be able to tackle anything too fancy.

    Thanks for your help!
  2. McG

    McG New Member

    Messages:
    33
    Location:
    CT, RI
    If the kickspace heater is on the return pipe coming off of the 3' of fin tube (in the same bathroom) - I can't see how the kickspace heater could contribute anything more than the residual heat not expressed by the fin tube which would not be considerable. A circulator on the 3/4" loop feeding these two elements might push more heat through them but only when the boiler is fired up. Jumping the circulator pump you're contemplating adding off of the primary circulator makes sense. It seems you're trying to create a second zone for this loop and the two elements on it. To do that, there may be other factors to consider and a more effective way to accomplish what you're after. That said, for all I know (I am not a pro and have never added a circulator or a pump to any heating system), what you're proposing may accomplish what you're after; to increase the heating factor in this bathroom during the "shoulder" months. I like that you used "scoop" tees. Can you tell me more about them and why you chose to use them?
  3. rrcur

    rrcur New Member

    Messages:
    14
    Location:
    Southern Maine
    McG,

    Thanks for the response. I'll try to clarify the situation.

    The 3/4" copper loop begins in the basement where it tees off of a black iron supply line. It then rises to the second floor bathroom where it connects to the 3 ft fin tube. Then it drops back to the basement where it contects by way of a tee to a black iron return pipe.

    I assumed that the fin tube would not strip ALL of the heat from the water in the 3/4" line, and that the water in the 3/4" line would be hot enough to provide heat for the toe kick heater that I installed on the first floor in a small vestibule, downstream from the fin tube.

    I piped the toe kick heater as recommended in the Beacon and Morris instruction manual, using a mono flow loop off of the existing 3/4" return line using 1/2" copper and two scoop tees.

    As things stand, I have almost no flow through the 3/4" loop. I feel heat for about the first 4 ft of 3/4" copper line, after it tees off of the black iron line. Strangely enough, I also feel some heat in the first couple feet of 3/4" copper RETURN line, just before it re-connects to the black iron return line. The fin tube is cold and the 1/2" lines in the mon-flow loop to the toe kick also feel cool.

    I'm pretty sure the loop is not air bound. I've bled it thoroughly from valves at the top of the loop at the fin tube and at the toe kick.

    I was just wondering if I could "boost" flow through the 3/4" loop with a small circulator pump, and, if so, how the wiring for this pump might connect to my existing thermostat wiring, and main circulator pump.

    Or am I describing a second zone which would require a second thermostat, zone valve, etc.?

    Thanks again for you feedback.
  4. Dana

    Dana In the trades

    Messages:
    3,028
    Location:
    01609
    This doesn't sound like low flow, it sounds like NO flow. The warmth you feel where it tees into the main supply & return lines is merely the conducted heat.

    Did you air-purge the loop after installing the kick heater? If it's airlocked this is the sort of behavior you should expect.
  5. rrcur

    rrcur New Member

    Messages:
    14
    Location:
    Southern Maine
    NO flow is right.

    I tried my best to purge the air, given the two drain/bleeder valve locations I have in the loop. I get a continuous water flow out of the bleeder valve at the end of the fin tube in the second floor bathroom. A tremendous amount of water comes through when I open the small drain/bleeder valve that I soldered into the 1/2" copper line that makes up the short mono-flow loop in the basement.

    Truth is, I got confused and put this drain/bleeder valve in the mono-flow loop BEFORE the toe kick. (Long embarrassing story behind this.) Probably should be AFTER the toe kick, right?

    But even if the toe kick is bound up, I'm surprised I get NO flow through the entire 3/4" loop. The mono-flow loop is sort of like an exit ramp, right? I thought the the main traffic would still flow right past the scoop tees in the 3/4" line.

    Any suggestions on how to get the air out?
  6. McG

    McG New Member

    Messages:
    33
    Location:
    CT, RI
    I've never used scoop tees, but I am wondering if they have an orientation that you may have reversed, resulting in the no-flow conditon you're experiencing.
  7. Dana

    Dana In the trades

    Messages:
    3,028
    Location:
    01609
    Sometimes it takes a fairly massive release of water at a high rate of flow the high point of the system to work all the air traps out, but it's system specific. You can't count on just running it until there's a good flow of water with no visible bubbles in it- run at least 10-20 gallons out, and don't be surprised if you have to run it more.

    Reversing monoflow tees would not block flow, but it would reduce the flow in the side loop.
  8. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    Though the toekick people often mention the monoflo system - perhaps wishing is is a cure-all for easy installation. I find the
    mono-flo a high technical design challenge i.e. not DIY friendly.

    We do not use toekicks unless fixing someone else's pour design but when we do flow is made certain by proper balancing from
    a common manifold. Like duct boosters, most pumps are energy wasting crutches. When mixing hydronic emitters - cast iron radiators,
    fin-tube, radiant floors, radiant ceilings, fin-tube baseboard and yes even the noisy comfort killing toe-kick fan coil, proper flow is
    made certain by careful pump sizing, near piping and air elimination including of course easy purging of each loop to a common drain.

    I have seen systems decades old that have always had air in them, wasting fuel and eating pumps. It pays to get it done right.

    Proof once again, that it is not the machine, but the man that counts most.

    Without pictures and experience, your problem is for the local hydronic expert...yes, he is not that far away.
  9. rrcur

    rrcur New Member

    Messages:
    14
    Location:
    Southern Maine
    Well, I was pretty sure the copper loop was air bound, so I put a boiler drain valve followed by a ball valve in the 3/4" copper return line, just before it tees back into the large iron return loop pipe in the basement. Closing the ball valve and opening the drain really let me purge the heck out of that loop.

    I'm going to call it a success because I now have decent flow to the fin tube in the upstairs bathroom, (like I did before I started messing with things) and the toe kick comes on at times when the boiler is really working hard. B and M is also sending me a lower temp thermostat (for free) so I exepect his to help get more warm air through the toe kick, even under not so great flow conditions.

    I had inherited the condition of a fin tube loop in a cast iron zone, which I know is not a great idea, from the previous owner. The idea here was to squeeze a little bit more heat out the fin tube loop for the upcoming coldest nights. I think I accomplished this.

    Thanks for the help!

    Next project: installing some salvaged cast iron baseboard.
  10. BadgerBoilerMN

    BadgerBoilerMN Master Hot Water Mpls,MN

    Messages:
    303
    Location:
    Minneapolis
    Well done. You may find the low temp switch blows a bit cool. Yours is a common situation we find in most kitchen remodels here in Minneapolis, when those old cast iron radiators are thrown away. Monoflow tees are more appropriate for fin-tube systems.
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