Advice on boiler temp setting

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  • StuckInTheMud
    Automated Home Lurker
    • Oct 2004
    • 6

    Advice on boiler temp setting

    I'm moving to having a thermostat in the house, and after advice on how the boiler temperature should be set.

    Up until now we've used the boiler temperate (plus on-time) to regulate the house temperature, crude and needs constant manual intervention as the weather changes.

    With a stat on the system, what level should the boiler be set to for optimum heating?

    My thoughts are that if it's low, rooms may take too long to warm up, if it's high it may be too quick and the controller starts to cycle too much, or is the high setting best so that things do get warm quick?



    Jim
  • geoff07
    Automated Home Jr Member
    • Dec 2013
    • 12

    #2
    Fit a weather compensator!

    Comment

    • MichaelD
      Automated Home Guru
      • Mar 2006
      • 167

      #3
      With room thermostats and a modern boiler, you should set the boiler on its highest heat setting, that will get everything warmed up quickly, then as the rooms reach their target temperature, the rad thermostats will turn off the heat to that radiator, to keep each room at the required temperature.

      As the radiators reduce the heat they take out of the circulating water, the return flow gets hotter, and the boiler will reduce the gas it burns to keep the output temperature at the right level.

      That is how a fully controlled system works, if you only have a single whole-house control, then you'll probably need to reduce the boiler temperature to stop the overall temperature from overshooting.

      You could always try it at 75%, then adjust up or down until it works right for your house.

      Comment

      • geoff07
        Automated Home Jr Member
        • Dec 2013
        • 12

        #4
        If you have a condensing boiler, make sure that the return temperature is no higher than 55 degrees when heating radiators, to ensure efficient heat recovery. Radiators are generally set up for an 11C drop so the flow temperature should be 66C. Ideally this would be managed by a control system that measures actual pipe temperatures.

        If your control system also knows the outside temperature then it can become a weather compensator designed to reduce the radiator temperature as the outside temperature increases. This will make it even more efficient, make the rooms more comfortable, and save a lot of money in wasted heat. However, you then need Hot Water Priority so that the tank can be heated to 60C to prevent legionella, which implies a higher return temperature than 55 when heating the water, albeit briefly.

        Comment

        • MichaelD
          Automated Home Guru
          • Mar 2006
          • 167

          #5
          Originally posted by geoff07 View Post
          If you have a condensing boiler, make sure that the return temperature is no higher than 55 degrees when heating radiators, to ensure efficient heat recovery.
          How can you do that with thermostatically controlled radiators? If all the rooms get hot, then hot water flows back to the boiler unused. What problems would >55 degrees cause?

          Comment

          • geoff07
            Automated Home Jr Member
            • Dec 2013
            • 12

            #6
            A condensing boiler is efficient because the return water is cool enough to condense the exhaust gasses, and thus recover the latent heat of evaporation of the water contained within the supplied gas. You already paid to evaporate it, now you get that energy back. It is this that makes a condensing boiler highly desirable, with efficiencies above 90%. But to do this the return water has to be cool enough. 55C is the recommended maximum return temp for this to work, though cooler is better.

            If your radiators are balanced and reasonably sized then the return temp should be around 11-12C below the flow temp if the weather is cold.

            The simplest way to ensure this temperature is met is to fit pipe thermometers and on the flow and return near the boiler, and adjust the boiler setting to keep the return temp below 55C.

            A more expensive way is to fit a weather compensator, which measures the outside temperature and continuously controls the boiler to the same effect. A more fun way, if you have the skills, is to build your own, as I did. Either way, the effect is to have your radiators taking cooler water for longer, more stable room temperatures, and considerably less running cost.

            Comment

            • MichaelD
              Automated Home Guru
              • Mar 2006
              • 167

              #7
              Interesting stuff. My Worcester Bosch reduces the gas burn when there isn't much heat needed, do you think this will be achieving the same effect?

              Comment

              • geoff07
                Automated Home Jr Member
                • Dec 2013
                • 12

                #8
                From what I can tell, it knows the return temperature and adjusts the flame accordingly. But it doesn't know the outside temperature so can't tell what radiator temp you really want.

                The other problem you have to consider is how to get the hot tank above 60C (legionella) whilst keeping the radiator return temp down. The solution is hot water priority i.e. separately heating the house and the water to different setpoints, for which you need separate zone valves (or a three-port valve that is fully one way or the other and never at the mid point), and a relay to cut off the space heating when there is hot water demand, plus the weather compensator.

                It is evident that more sophisticated controls that do this will save perhaps 20% of gas consumption, and that almost no houses in the UK have such controls. Limited data so far from all the measures that I have taken is already showing a reduction of at least 20%, which for me is worth £250 pa.

                Comment

                • MichaelD
                  Automated Home Guru
                  • Mar 2006
                  • 167

                  #9
                  As this is a combi boiler, presumably its safe to assume that legionella won't be an issue? I never want the hot water to come out of the tap at 60 degrees, that would be painful

                  I do weather compensation in a different way. My system checks the BBC website to see the forecast, and trims the 'thermostat' dependent on the expected temperature. It also reduces it a little if its expected to be sunny (solar gain).

                  To get the house to 20 degrees when we wake up, the system checks Outlook to see what time we are waking that day (wake-up is set as an appointment), considers the current temperature in the house, takes account of the outside temperature, and starts the boiler at the right time to hit 20 at the wake up time. Once the motion sensor on the landing sees that we are out of bed, it shuts off the upstairs heating zone valve, and residual heat keeps us warm until we go downstairs

                  The radiators all have a honeywell HR80, effectively giving me 10 zones in the house, but I don't adjust their temperature dependent on the weather, they just do their stuff to get the room to 21 degrees when needed, all the sophisticated control is done on the boiler.

                  Comment

                  • biccies
                    Automated Home Jr Member
                    • Nov 2012
                    • 39

                    #10
                    That sounds like quite the system Michael, very similar to what I'm hoping to achieve

                    Comment

                    • geoff07
                      Automated Home Jr Member
                      • Dec 2013
                      • 12

                      #11
                      Of course, if you don't have a hot tank you don't need to be concerned about Legionella as long as any long hot pipe runs are flushed periodically. For those that do have tanks, a tempering valve (mixer) at the output from the tank is the solution to too-hot water.

                      The weather compensator doesn't affect the radiator settings, they remain as you want. It just reduces the circulating temperature. Ideally, the circulating temp will be just right to keep the rooms as you want them without constant changes to the radiator settings (heat gain = heat loss). But that requires getting the weather compensator slope just right for your building (thermal mass, losses, on/off schedule) and is a bit tricky to get right.

                      Comment

                      • Kovacs
                        Automated Home Lurker
                        • Feb 2014
                        • 4

                        #12
                        We have a Valiant Ecotec plus system boiler and HW cylinder. Recently I've invested in some independently controllable TRVs for the rooms both up and downstairs (the Pegler iTemps) and am happy so far with these as they allow us to not heat rooms/areas that aren't being used or at the least, have good control over the temperatures in those rooms.

                        Further savings should also come from the Tado thermostat and boiler controller that have been installed which amongst other things, will use presence detection to pick up when the wife and I are out of the house and reduce the house temperature according to how far away we are.

                        Reading on here though, as we do have a condensing boiler and I understand that the flow temps ideally want to be moderated depending on the outside temp, which weather compensator would do the job? Most of the ones I've seen want to be your thermostat/timer as well, but I don't want or need any of that. I'd like to just ensure the flow temp is set to an optimum level. Any suggestions on what would be a good option for this?

                        Comment

                        • martyn.wendon
                          Automated Home Jr Member
                          • Dec 2013
                          • 41

                          #13
                          Originally posted by Kovacs View Post
                          Reading on here though, as we do have a condensing boiler and I understand that the flow temps ideally want to be moderated depending on the outside temp, which weather compensator would do the job? Most of the ones I've seen want to be your thermostat/timer as well, but I don't want or need any of that. I'd like to just ensure the flow temp is set to an optimum level. Any suggestions on what would be a good option for this?
                          I had a new Vaillant combi boiler installed about 3 years or so ago to replace an ageing 30+ year gravity based system. At that time, I was using the HouseHeat / ELV / Conrad FS20 based thermostats, radiator valves and boiler interlock to great effect, but I was persuaded by the gas installer to remove it all and fit the Vaillant weather compensator instead. What a bag of poop that was :-(

                          As a family we just couldn't get on with it, the heating seemed to be on nearly all the time, like coming on "gently" at 3am just so that by 7am when the schedule was supposed to kick in it was "warm" for the hour we have the heating on in the mornings. Or refusing to come on at all, even though the house felt chilly. I understand the principle of weather compensators and I persevered with it for a couple of months before finally removing it and re-fitting my previous solution :-)

                          Since I already had full control and reporting of the radiators and boiler I just use an input into my HA system from an external temperature sensor. When it's colder outside, I set all the rooms set-point + a few degrees. When it's warmer outside, I set all the rooms set-point - a few degrees. I also measure and record the temperature of the flow and return pipes in the HA system and then set the flow temp on the boiler and balance all the radiators at the lock-shield end to hit a sweet point on the return temp. This works really well - I know it's not *true* weather compensation but it still saves money and compared to the mess with the Vaillant weather comp at least it has family approval!


                          Hope that helps!
                          Martyn Wendon
                          Vesternet
                          Check out my Blog!

                          Comment

                          • geoff07
                            Automated Home Jr Member
                            • Dec 2013
                            • 12

                            #14
                            If your boiler manufacturer makes a weather compensator, then that is likely to integrate better with your boiler, possibly even physically in the cabinet. Though the report above isn't too promising in the case of Valliant. Ideally, it would adjust the setpoint in the boiler electronics directly. In my case, the WB condensing boiler at my house only has room-stat on/off control, so I made my own weather compensator with a relay that takes the place of the room stat. It does the job well but is another box on the wall, and makes hot-water priority a bit more of a fiddle. I also have the Conrad actuators, with their gubbins that listens on the radio to the radiator settings and cuts out the boiler if there is no soft-zone demand.

                            Comment

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