Page 1 of 2 12 LastLast
Results 1 to 10 of 14

Thread: Advice on boiler temp setting

  1. #1
    Automated Home Lurker
    Join Date
    Oct 2004
    Posts
    4

    Default 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

  2. #2
    Automated Home Jr Member
    Join Date
    Dec 2013
    Posts
    12

    Default

    Fit a weather compensator!

  3. #3
    Automated Home Guru MichaelD's Avatar
    Join Date
    Mar 2006
    Location
    Lancashire
    Posts
    163

    Default

    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.

  4. #4
    Automated Home Jr Member
    Join Date
    Dec 2013
    Posts
    12

    Default

    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.

  5. #5
    Automated Home Guru MichaelD's Avatar
    Join Date
    Mar 2006
    Location
    Lancashire
    Posts
    163

    Default

    Quote 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?

  6. #6
    Automated Home Jr Member
    Join Date
    Dec 2013
    Posts
    12

    Default

    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.

  7. #7
    Automated Home Guru MichaelD's Avatar
    Join Date
    Mar 2006
    Location
    Lancashire
    Posts
    163

    Default

    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?

  8. #8
    Automated Home Jr Member
    Join Date
    Dec 2013
    Posts
    12

    Default

    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.

  9. #9
    Automated Home Guru MichaelD's Avatar
    Join Date
    Mar 2006
    Location
    Lancashire
    Posts
    163

    Default

    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.

  10. #10
    Automated Home Jr Member
    Join Date
    Nov 2012
    Posts
    39

    Default

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

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •