Flow temp settings etc. to save energy
We have a Worcester Bosch boiler and this spring installed a few tado radiator valves, a tado smart thermostat for the whole central heating system, as well as a separate wired thermostat for the underfloor heating in the kitchen. Given the cost of fuel, we want this to be as energy efficient as possible come the winter. I see many commentators in the news talking about lowering the boiler's flow temperature. Does this make any sense with a tado system? I assumed the higher temp most efficient to get the heat to the correct level asap? Or does tado control all of this anyway?
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A gas boiler will start condensing when the water returning from the radiators to the boiler is below 56°C. The lower the return temperature the more condensing will happen. The condensing is recovering energy from the flu gases.
There are a number of ways to reduce the return temperature.
1) Reduce the flow temperature.
2) Balance your radiators. The delta between the flow and return should be between 12°C and 20°C. If a radiator is particularly hot compared to others then the balance is probably wrong - meaning the returning water temperature for the radiator is too high.
3) Reduce the pump speed. The slower the water circulates through the pipes the more heat it loses before returning to the boiler. Too slow and the last radiator will not heat up properly.
4) Use a weather compensation device to adjust the flow temperature according to the outside temperature. On cold days the radiators will be hotter, but on mild days the radiators will be cooler than normal.
If your Tado thermostat is using traditional relay mode the flow temperature will not be adjusted. If it's set to 75°C on the boiler then it will always be that temperature.
If your Tado thermostat is using the digital interface the flow temperature will be adjusted according to the room temperature. When the room is cold the flow temperature is higher, but the flow temperature is reduced when the room temperature is close to the target temperature.
If you have a system boiler with a hot water cylinder then you cannot lower the flow temperature too much. You need to store hot water above 60°C to avoid issues with bacterial growth. For combi boilers it's not an issue.
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Many thanks for the this helpful reply. We have a combi boiler - a Worcester Bosch 34Cdi Greenstar. How can I tell if the tado thermostat is using the digital interface or relay? Presumably if the former then it will take care of all the settings you mention?
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If it’s a uk wireless receiver it’s unlikely to be using a digital connection because Tado removed support for it, if it’s a wired thermostat there’s a possibility it is. Is there a hot water square on your app that allows you to set the temperature? If so it’s probably using a digital connection.
You should be able to look in your boiler’s menu to see what kind of connection it’s using if it has a digital display.0 -
Check your original wiring instructions supplied by Tado or look at the wiring inside the actual thermostat. Wiring on the left for relay mode and on the right for digital mode.
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Many thanks for your replies. The wired thermostat that does the underfloor heating is in relay mode. We also have a wireless thermostat that does the rest of the heating, which presumably is in relay mode as well. Do you have a suggestion for the temperature to set the boiler at? I'd like it to be as energy efficient as possible so not sure whether a lower temperature works best or, given each of the rooms we're heating have their own thermostat, whether a higher boiler temp would be better to get the heat to the right temp faster?
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A high temperature will never be more efficient. I'd recommend doing a manual type of weather compensation through the winter season. It won't cost you anything, other than time.
When you turn your heating back on (October?) set the flow temperature to 50°C and see how the house feels when warming up. If the rooms don't reach their target temperature you may need to increase the flow above 50°C. In November increase the flow temperature by a few degrees, and do the same again in December and January. In February you can start to lower the flow temperature and continue to lower until the end of the heating season.
If January is 15°C colder outdoors than October, then you'll probably want your boiler flow temperature to be 15°C higher.
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That's very helpful - thank you.
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You can also use the tado installer app. There’s no registration to use it. Fire it up on your phone and scan the QR code on the tado hub and it will find your system.
I have a Worcester Bosch 34CDi and the app tells me it’s using a digital connection and the HT-Bus protocol. It also shows the flow temperature which should match the boiler display.
As this is a combi boiler I can’t control hot water temperature with tado but I do have an on/off setting which controls the pre-heat setting with a schedule. I have this scheduled to only be on during the day which just means that overnight you have to wait a little longer for hot water at the tap.0 -
In most cases you can control hot water temperature on a combi connected digitally. It might be that Tado doesn’t support it on your boiler’s ebus protocol.0
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@michaelamherst this article provides a good overview: https://www.theheatinghub.co.uk/articles/turn-down-the-boiler-flow-temperature
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Oh, and there’s definitely a sweet spot with flow temp. Both too high and too low can be inefficient. Trial and error and a lot of attention to smart meter IHD required.0
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Interesting, Im curious as to what you set your room and setback too and whether you just have it all on the same schedule?
I picked up enough TRVS to go from 2 and a wired device to 7 (one on each rad)
Im finding myself forever tinkering as some rooms are colder than others and then the boiler is firing up at 1am to heat the kitchen for no one for 6 hours to maintain 17 instead of 15 or whatever.
Doesnt really help that tados graphs are atrocious with 14-19 on one, 17-20 on another, no marks between or an overall combined chart and then the lines to call for heat 1-2-3 dont really tell me much either tbh
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What I'm seeing is, at 55°C the boiler works in 2 modes: 30 seconds heating + 2 minutes for water pump?
That gives 50 on / off cycles per hour. This doesn't seem appropriate for boiler's lifespan.
@andertl and @ValiE have similar observations https://community.tado.com/en-gb/discussion/comment/53108#Comment_53108
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Hi.
Just wanted to run my thoughts by you on flow temp and eBus (especially when using early start)
The lower the flow temp, the earlier “early start” has to start. (Try saying that when you’re drunk 😂).
Using eBus, we know Tado controls flow temp. So does it not make sense to run max flow temp as high as possible.
-early start begins to heat the house - 75
-house reaches the desired temperature quickly
-Tado scales back the flow temp to the most efficient temperature to maintain room temperature
Because the other option is to turn flow temp down to 50. But early start would have to start to the previous week to heat the house 😂.
So my thinking is. Assuming your rads are correctly sized, connect via eBus, set max flow temp to max, and let Tado do its thing….
What do you think?0 -
Condensing boilers become much more inefficient when producing heat above the dew point (55c) so while you’re likely to get a house warmer quickly, you’ll also use more energy to do so. If you set the max flow temp too low and you like a warm house, you might find that your heating never reaches the target temperature. It’s all about finding the sweet spot between efficiency and comfort.0
