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What speed should a circulating pump be set at ?

  • 08-11-2015 3:21pm
    #1
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭


    Hi,

    I have oil fired central heating, I've also got a solid fuel boiler stove, that I use to heat the rads instead of the oil most of the time.

    My circulating pump has three speed settings, which speed is the optimal one ?

    I've it set to the medium speed.

    Also, separate question : Very occasionally I get a little bit of air built up in the system and I have to bleed the circulating pump. I can tell when it's needed because the pump get's a little noisy, and once the air is bled out it runs nice and smooth again. I only have to do this about once every 3 weeks or so, and its a 2 minute job.

    Is this the best way to do it, or is there a better way. I've tried bleeding the rads instead at times, but very little if any air is ever in them, I find what little air there is gathers around the circulating pump first. The circulating pump is located in the hot press upstairs.


Comments

  • #2
    Walter Becket
    Registered Users, Registered Users 2 Posts: 152 ✭✭Walter Becket


    If the pump speed is heigh then the pipe stat will be switching a lot and will ware out sooner. If the speed is too slow it may not be able to get the heat away from the stove quick enough.


  • #3
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭La Fenetre


    Also I suppose if the speed was high, the stove wouldn't get the chance to heat the water, and too slow the water gets cooling too much before it gets back to the stove ?


  • #4
    Walter Becket
    Registered Users, Registered Users 2 Posts: 152 ✭✭Walter Becket


    Your order question. This should not be happening air is somehow getting into the system. The circulation pump should be able to clear a small amount of air from itself if installed correctly. It should be pumping up or along but not down.


  • #5
    The Sidewards Man
    Banned (with Prison Access) Posts: 1,570 ✭✭✭The Sidewards Man


    Was the stove installed by an engineer or by a youtuber mens shed hero?


  • #6
    Walter Becket
    Registered Users, Registered Users 2 Posts: 152 ✭✭Walter Becket


    La Fenetre wrote: »
    Also I suppose if the speed was high, the stove wouldn't get the chance to heat the water, and too slow the water gets cooling too much before it gets back to the stove ?

    If you mean the water in the hot cylinder, then the pump speed should not affect it because the pump only runs when the pipestat calls for it. The stat should be set heigh enough to allow the hot cylinder to reach 60deg.


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  • #7
    Wearb
    Moderators, Home & Garden Moderators Posts: 6,380 Mod ✭✭✭✭Wearb


    It is important that the pump has the correct orientation. Post a pick of it. Put a ruler or brush handle exactly verticaly beside it for a reference.

    Please follow site and charter rules. "Resistance is futile"



  • #8
    Dtp1979
    Registered Users, Registered Users 2 Posts: 12,870 ✭✭✭✭Dtp1979


    Pump speed will depend on syst design. Nothing to do with heating the water in the cylinder. Speed 2 will be higher on a 6m pump than on a 5.
    Pump sizes have to be carefully calculated on open vented systems as it can cause air to be drawn into the system on pump start up, which is why your prob getting air in the pump.
    2/3 the head height should be the min distance between the attic tank and the highest part of the pumped circuit


  • #9
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭La Fenetre


    No I mean heating the water for the rads, not the cylinder


  • #10
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭La Fenetre


    Walter Becket wrote: »
    Your order question. This should not be happening air is somehow getting into the system. The circulation pump should be able to clear a small amount of air from itself if installed correctly. It should be pumping up or along but not down.

    I was thinking that, thing is I'd say it would be pretty hard to find where the small amount of air is getting in, I can find no trace of it, and as it's having very little effect, other than having to do a 2 min bleed once every 3 weeks or so, I can live with it.


  • #11
    Dtp1979
    Registered Users, Registered Users 2 Posts: 12,870 ✭✭✭✭Dtp1979


    La Fenetre wrote: »
    No I mean heating the water for the rads, not the cylinder

    No that wouldn't be an issue with a stove because that's when the thermostat comes into play. It allows the drive to re heat the water before pumping it away


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  • #12
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭La Fenetre


    The Sidewards Man wrote: »
    Was the stove installed by an engineer or by a youtuber mens shed hero?

    It was installed about 10 years ago, by a very good qualified plumber with about 30 years experience. I doubt he has a degree or is a member of IEI. I know some women and the media find the idea of rounding older men up and locking them away in sheds at the back of the garden very appealing.


  • #13
    Walter Becket
    Registered Users, Registered Users 2 Posts: 152 ✭✭Walter Becket


    La Fenetre wrote: »
    I was thinking that, thing is I'd say it would be pretty hard to find where the small amount of air is getting in, I can find no trace of it, and as it's having very little effect, other than having to do a 2 min bleed once every 3 weeks or so, I can live with it.

    Air is bad it causes the rads to rust away you will eventually get leaky rads.


  • #14
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭La Fenetre


    Dtp1979 wrote: »
    No that wouldn't be an issue with a stove because that's when the thermostat comes into play. It allows the drive to re heat the water before pumping it away

    I know, I was asking about the optimum circulation pump speed for heating the rads, not the hot water cylinder. When I talk about heating the water I'm referring to heating water for rads not the hot water cylinder. The cylinder thermostat has no issue, and does not dictate the circulating pump speed. As far as I can tell the general consensus seems to be leave it on medium speed.


  • #15
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭La Fenetre


    Walter Becket wrote: »
    Air is bad it causes the rads to rust away you will eventually get leaky rads.

    The amount of air really is very very little, is it worth getting in the plumber to pressure test the whole lot and try and find it or not ?


  • #16
    Dtp1979
    Registered Users, Registered Users 2 Posts: 12,870 ✭✭✭✭Dtp1979


    La Fenetre wrote: »
    I know, I was asking about the optimum circulation pump speed for heating the rads, not the hot water cylinder. When I talk about heating the water I'm referring to heating water for rads not the hot water cylinder. The cylinder thermostat has no issue, and does not dictate the circulating pump speed. As far as I can tell the general consensus seems to be leave it on medium speed.

    Read my first post when I replied


  • #17
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭La Fenetre


    Dtp1979 wrote: »
    Pump speed will depend on syst design. Nothing to do with heating the water in the cylinder.

    I know its nothing to do with the heating the hot water in the cylinder. When I said heating water, I was talking about heating the water for the rads. The only reason I mentioned the cylinder was to describe the location of the pump. That seems to be confusing some people.
    Dtp1979 wrote: »
    Speed 2 will be higher on a 6m pump than on a 5.
    Pump sizes have to be carefully calculated on open vented systems as it can cause air to be drawn into the system on pump start up, which is why your prob getting air in the pump.
    2/3 the head height should be the min distance between the attic tank and the highest part of the pumped circuit



    Regarding the air, so is that 2/3'rds of 6m or 5 (depending on pump), so is that 4m / 3.33m for min. distance between attic tank and highest part of pumped circuit ? I don't know many houses with the circulating pump in the upstairs hot press that would have that, or is that what you are saying ?


  • #18
    Dtp1979
    Registered Users, Registered Users 2 Posts: 12,870 ✭✭✭✭Dtp1979


    La Fenetre wrote: »
    I know its nothing to do with the heating the hot water in the cylinder. When I said heating water, I was talking about heating the water for the rads. The only reason I mentioned the cylinder was to describe the location of the pump. That seems to be confusing some people.



    Regarding the air, so is that 2/3'rds of 6m or 5 (depending on pump), so is that 4m / 3.33m for min. distance between attic tank and highest part of pumped circuit ? I don't know many houses with the circulating pump in the upstairs hot press that would have that, or is that what you are saying ?

    Yes that's what I'm saying. The highest part of the pumped circuit would be a radiator. If you can't get at least 3.3m from it to the tank then you put in a smaller pump or turn the speed down because it will cause system problems such as trapped air in the pump, oxidation in the water. But I'm not complaining, bad heating system design by other plumbers is what has me so busy


  • #19
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭La Fenetre


    Dtp1979 wrote: »
    Yes that's what I'm saying. The highest part of the pumped circuit would be a radiator. If you can't get at least 3.3m from it to the tank then you put in a smaller pump or turn the speed down because it will cause system problems such as trapped air in the pump, oxidation in the water. But I'm not complaining, bad heating system design by other plumbers is what has me so busy

    Thanks, is that measured from the top of the highest rad to the top water level in the expansion tank ? BTW, I'm not complaining about my plumbing either, I've found it excellent over the 10 years, used every day, fault free, apart from this very very small amount of air I had the question about. Apart from the day it was put in, no plumber got any work in our house.


  • #20
    Dtp1979
    Registered Users, Registered Users 2 Posts: 12,870 ✭✭✭✭Dtp1979


    La Fenetre wrote: »
    Thanks, is that measured from the top of the highest rad to the top water level in the expansion tank ? BTW, I'm not complaining about my plumbing either, I've found it excellent over the 10 years, used every day, fault free, apart from this very very small amount of air I had the question about. Apart from the day it was put in, no plumber got any work in our house.

    From top of the rad to water line I think.


  • #21
    Walter Becket
    Registered Users, Registered Users 2 Posts: 152 ✭✭Walter Becket


    La Fenetre wrote: »
    The amount of air really is very very little, is it worth getting in the plumber to pressure test the whole lot and try and find it or not ?

    There are some things you could check.
    When the pump is running is there any water coming from the vent pipe (that's the pipe that is terminating above the small tank in the attic this water will be splashing into the tank from above) if there is it absorbes air as it splashes.
    When the system is cold is there any water coming onto the tank from the ballcock if so you have a leak and new water brings new air.
    Is there an automatic air vent on the pipework in a location where the pump could be creating a vacuum these vents can admit air.
    Rad. valves can admit air this is difficult to find.


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  • #22
    La Fenetre
    Registered Users, Registered Users 2 Posts: 736 ✭✭✭La Fenetre


    Walter Becket wrote: »
    There are some things you could check.
    When the pump is running is there any water coming from the vent pipe (that's the pipe that is terminating above the small tank in the attic this water will be splashing into the tank from above) if there is it absorbes air as it splashes.
    When the system is cold is there any water coming onto the tank from the ballcock if so you have a leak and new water brings new air.
    Is there an automatic air vent on the pipework in a location where the pump could be creating a vacuum these vents can admit air.
    Rad. valves can admit air this is difficult to find.

    Thanks Walter, I've never noticed any of the above, but I'll keep an eye on it. The amount of air is very small and infrequent, I guess I'm being a bit over fussy if anything, because I've no other issues with the system at all, so I suspect it'll be hard to find.


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