Weather Compensation


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In my continual quest for efficiency and less gas consumption I have just taken delivery of a Weather Compensation Kit for my boiler, which I will fit this coming weekend.

Not a requirement in the UK, yet mandatory in several continental countries, a Weather Compensation kit monitors the outside air temperature and varies your boiler's flow temperature. eg. as the outside temperature drops, the boiler temperature increases.

The reasoning behind this is as follows. Heat loss from a building is proportional to the difference in temperature between inside and outside. Therefore, in order to maintain a comfortable room temperature on very cold days you need to put more heat through your radiators. Turning your room thermostat up doesn't do that (though that's what most of us do!). To get more heat into the room you have to turn the boiler thermostat up. Conversely, when the weather warms up you should turn the boiler thermostat down so you don't waste gas and money.

There would seem to be two benefits to fitting a Weather Compensation Kit. One is that your house should keep warm even on the coldest of days. The second is the boiler will turn itself down on warmer days, ensuring the boiler is always working in its most efficient condensing mode, thereby saving you money.

Most modern, condensing boilers can be fitted with Weather Compensation Kits. Mine cost £21, delivered, from Amazon.

I will follow this thread up after a month and let you know if I see any difference in comfort levels and/or gas consumption.

Meanwhile, anyone got a Weather Compensation Kit fitted to their boiler and if so, do you have any pointers that might help me set it up?

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Done it. Weather Compensation kit installed in less than an hour; and I spent most of that shifting stuff in the garage so I could run the cable from the boiler to the outside sensor.

Now comes the interesting bit. Ideally, for this to work, the boiler should automatically raise or lower the flow temperature; that is the temperature of the water to the radiators. As I said in my previous post, if the outside temperature drops, the boiler flow temperature should increase. That's something I'll be able to check when we get a really cold snap, or we see the sun again sometime next spring.

Meanwhile I have increased the room thermostat to 30 degrees. Why? I want to see at what temperature the room will eventually stabilise and I don't want the boiler stopping and starting every few minutes.
If the room stabilises at a lower temperature than we are comfortable with I'll turn the boiler stat up a touch. This being an old house it will never be as efficient as a modern build.


It's 5 degrees outside today and the boiler flow temperature is 56 degrees,
which is bang-on the 21 degree room temperature curve graph that came with the kit. T
he return flow is 41 degrees. The boiler has turned itself right down and is, I hope, sipping gas instead of guzzling it.

Here's a good article on Weather Compensation https://www.installeronline.co.uk/34166-2/
This is really interesting @Oakbank 🆙
Looks like you're at the cutting edge!
How soon will you be able to tell if it'll work? Or are you already satisfied it's going to?
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hi Oak, interesting. Does it just shut off the burner when the required temperature differential has been reached or is it more sophisticated? (I can't see it being terribly sophisticated for that price)
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Marc.
It is interesting right enough. The sophistication is in the boiler, not the weather compensation kit, which is nothing more than a thermistor in a weatherproof enclosure. Installation couldn't be simpler: 1) Screw kit to external, north-facing wall. 2) run wire from kit to boiler. 3) terminate into the kit at one end and a plug (supplied) at the the boiler end. 4) turn boiler off at the mains 5) push the plug into the weather compensation socket on the boiler control board. 6) power boiler back up.

The boiler automatically recognises weather compensation has been fitted and changes its operating mode from a fixed flow temperature controlled by the boiler thermostat, to a variable flow temperature controlled by the outside temperature. The central heating programmer and room thermostat still work, but if (and it's a big IF) you can balance your system by adjusting the boiler stat there should be little or no need for the room thermostat to turn the boiler on and off. The boiler should run for much longer periods at much lower and efficient temperatures.

This page from the manual makes things a bit clearer than perhaps I can.

1538
Oakbank;20541:
Marc.
It is interesting right enough. The sophistication is in the boiler, not the weather compensation kit, which is nothing more than a thermistor in a weatherproof enclosure. Installation couldn't be simpler: 1) Screw kit to external, north-facing wall. 2) run wire from kit to boiler. 3) terminate into the kit at one end and a plug (supplied) at the the boiler end. 4) turn boiler off at the mains 5) push the plug into the weather compensation socket on the boiler control board. 6) power boiler back up.

The boiler automatically recognises weather compensation has been fitted and changes its operating mode from a fixed flow temperature controlled by the boiler thermostat, to a variable flow temperature controlled by the outside temperature. The central heating programmer and room thermostat still work, but if (and it's a big IF) you can balance your system by adjusting the boiler stat there should be little or no need for the room thermostat to turn the boiler on and off. The boiler should run for much longer periods at much lower and efficient temperatures.

This page from the manual makes things a bit clearer than perhaps I can.

1538


Hi Oakbank. Thanks for all this information. I'm going to look into this for myself. Might wait until you confirm any gains before I buy though 😂 Cheers
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hi oakbank
if you can still edit your post can you re-attach as it hasn't worked (forum bug - edit and reattach usually cures it for me)
Is the socket mentioned standard on all modern boilers?
Oakbank;20541:
Marc.
It is interesting right enough. The sophistication is in the boiler, not the weather compensation kit, which is nothing more than a thermistor in a weatherproof enclosure. Installation couldn't be simpler: 1) Screw kit to external, north-facing wall. 2) run wire from kit to boiler. 3) terminate into the kit at one end and a plug (supplied) at the the boiler end. 4) turn boiler off at the mains 5) push the plug into the weather compensation socket on the boiler control board. 6) power boiler back up.

The boiler automatically recognises weather compensation has been fitted and changes its operating mode from a fixed flow temperature controlled by the boiler thermostat, to a variable flow temperature controlled by the outside temperature. The central heating programmer and room thermostat still work, but if (and it's a big IF) you can balance your system by adjusting the boiler stat there should be little or no need for the room thermostat to turn the boiler on and off. The boiler should run for much longer periods at much lower and efficient temperatures.

This page from the manual makes things a bit clearer than perhaps I can.

1538
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Hi Woz

To late to edit, but with a bit of luck it will work this time.


That looks a bit better, hope you can make it out. If you look at the 21 degree curve, dotted line right in the middle, you will see at 10 degrees outside the flow temperature should be @49 degrees, while at -5 outside it should be @68 degrees.
As I write the outside air temp is 6 degrees and the boiler flow temp is 55 degrees. That sounds relatively cool, I can keep my hand on the radiators, but the house is at 21 degrees while the boiler is running at a constant low fire. The room thermostat is at 21.5. I've set it at that so that when we fire up the log burner the central heating will go off.
@woz: I can only speak for my Ideal Logic Heat boiler, but looking at other manufacturer's info it appears all modern condensing boilers, including combi, have weather compensation built in, you only need the thermistor kit.
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@ oakbank
Much appreciated, thank you.
Presumably the thermistor enclosure has to sit outside the house? If so that's the first snag..my boiler is high up.
It will be interesting to see if this impacts your gas usage.
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Early days yet I know, but there are signs weather compensation is going to save me a bob or two.

Calculated average cubic feet per day for the month of December: 521
Actual measured cubic feet 5/6 Jan without weather compensation: 522
Actual measured cubic feet 6/7 Jan with weather compensation: 464
Actual measured cubic feet 7/8 Jan with weather compensation: 451


That works out at around 50p/day. Some might say "That doesn't sound like much of a saving", but it's around £180/year, which is more than December's expenditure on gas!
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hi Oak
I'm curious (I know one day it will be my undoing..) what method did you use to calculate your average for December or was it purely historic? I'm impressed that it's so close to reality but I can't see, given the vagaries of outside temp, how you could predict it so accurately?
Do you think that the saving is solely due to the boiler efficiency gains? If so that's really interesting.
Oakbank;20806:
Early days yet I know, but there are signs weather compensation is going to save me a bob or two.

Calculated average cubic feet per day for the month of December: 521
Actual measured cubic feet 5/6 Jan without weather compensation: 522
Actual measured cubic feet 6/7 Jan with weather compensation: 464
Actual measured cubic feet 7/8 Jan with weather compensation: 451


That works out at around 50p/day. Some might say "That doesn't sound like much of a saving", but it's around £180/year, which is more than December's expenditure on gas!
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Woz

Looked at the meter readings I submitted 2nd December to 2nd January divide by number of days. Simples.

The only thoughts I have regarding boiler efficiency are:-
1) The boiler flow and return temperatures are cooler than before, but should vary automatically with outside temp.
2) The room temperature is as before but the thermostat is switching less often.

Like I said, early days.
How's this going @Oakbank ?
I think other Members will be interested in getting one of these. 🆙
I'm thinking this could be turned into a 10-step guide on 'How to install and read a weather compensation kit'. A sort of how-to article for the community.
What do you think?
Hi all, this is a really interesting thread introducing me to something completely new, so thanks to @Oakbank for sharing.
I'm now thinking about possibly installing one sometime this year but have one question.....
Does anyone know if this would still be of use in a house without a thermostat? When we replaced all the radiators, our plumber said we didn't need one (the radiators all have TRVs).
Logic suggests that the principle should still hold true, but would be interested to see if anyone knows for sure.
Ta muchly in advance.
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Marc

So far Weather Compensation is doing what it says on the tin; lowering the boiler temperature when the ambient temperature increases and raising it in cold snaps. I've been taking daily readings and plugging the numbers into a spreadsheet.

The recent cold snap this past week, when temperatures went sub-zero for a few days, raised the daily gas consumption up to @ 490 cuft/day.
When ambient temperatures are higher, around the 5 - 10 degrees, daily consumption drops to @ 385 cuft/day.
January's average was @ 521 cuft/day.

I am confident the greatest savings will be made outside of the winter months when the boiler will throttle right back and sip gas.

I found tuning the system interesting. I finally settled on adjusting the boiler until the return temperature was @ 50 degrees, thus ensuring maximum heat recovery from condensation plus an acceptable room warm-up time from cold.

The volume of condensate being discharged from the boiler has increased substantially and the steam plume from the flue has reduced. I do wonder if these houses with a massive steam plume from the condensing boilers are actually condensing at all. My suspicion is they are not and have the boiler turned up too high.

Regards Installation: For my Ideal boiler, installation is a DIY job. You do not have to be a certified electrician or central heating engineer. I downloaded the installation instructions from my boiler manufacturer's website. I would expect other manufacturers to provide the same service.

Note: You may (I did) require a minor change to the wiring between your central heating controller and boiler. This is to ensure you get maximum heat when calling for hot water rather than the lower temperature you might get thanks to weather compensation.
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Ailsa

Personally I would always want a room thermostat. My experience of TRVs is they are good for throttling back the radiators in unused bedrooms, but not so good for maintaining a comfortable temperature in the inhabited room.

What I have noticed, and as I mentioned earlier, since installing weather compensation the radiators are not much hotter than they need to be to maintain a comfortable living room temperature. I initially thought I could tune the system such that the room thermostat would never switch the heating off. In practice this meant the warm up time, from cold, was too long. It got there in the end, but who likes getting out of bed when the house is still 'cool'.
By setting the boiler return temperature at @ 50 degrees (it must be below 55 degrees for condensation to take place) I achieved a decent warm-up time and the room thermostat still operates, albeit less frequently.

Hope this helps.


Ailsa;21893:
Hi all, this is a really interesting thread introducing me to something completely new, so thanks to @Oakbank for sharing.
I'm now thinking about possibly installing one sometime this year but have one question.....
Does anyone know if this would still be of use in a house without a thermostat? When we replaced all the radiators, our plumber said we didn't need one (the radiators all have TRVs).
Logic suggests that the principle should still hold true, but would be interested to see if anyone knows for sure.
Ta muchly in advance.
Thanks @Oakbank, will have a think about a thermostat as well as the weather compensation kit 🙂
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hi Oak
What was the wiring change?
Oakbank;21894:
Marc

So far Weather Compensation is doing what it says on the tin; lowering the boiler temperature when the ambient temperature increases and raising it in cold snaps. I've been taking daily readings and plugging the numbers into a spreadsheet.

The recent cold snap this past week, when temperatures went sub-zero for a few days, raised the daily gas consumption up to @ 490 cuft/day.
When ambient temperatures are higher, around the 5 - 10 degrees, daily consumption drops to @ 385 cuft/day.
January's average was @ 521 cuft/day.

I am confident the greatest savings will be made outside of the winter months when the boiler will throttle right back and sip gas.

I found tuning the system interesting. I finally settled on adjusting the boiler until the return temperature was @ 50 degrees, thus ensuring maximum heat recovery from condensation plus an acceptable room warm-up time from cold.

The volume of condensate being discharged from the boiler has increased substantially and the steam plume from the flue has reduced. I do wonder if these houses with a massive steam plume from the condensing boilers are actually condensing at all. My suspicion is they are not and have the boiler turned up too high.

Regards Installation: For my Ideal boiler, installation is a DIY job. You do not have to be a certified electrician or central heating engineer. I downloaded the installation instructions from my boiler manufacturer's website. I would expect other manufacturers to provide the same service.

Note: You may (I did) require a minor change to the wiring between your central heating controller and boiler. This is to ensure you get maximum heat when calling for hot water rather than the lower temperature you might get thanks to weather compensation.
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Woz

Hard to describe, and I suspect different boiler manufacturers might deal with it differently.
Basically the boiler needs to know when the controller is calling for hot water, override the weather compensation and turn the boiler temp to max, and use the hot water tank thermostat to limit the temperature.
If you don't modify the wiring the hot water will only get as hot as the boiler flow temperature under weather compensation control, which might not be hot enough on a warmish day.
My kit came with the wiring details.


woz;21904:
hi Oak
What was the wiring change?
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ahh thanks, mines a combi which has 2 discrete systems and temp settings on the front, one for HW temp the other CH temp, so not applicable; I guess any interaction will be controlled by the innards of the boiler while creating HW, which probably throttles the CH part temporarily.
Oakbank;21916:
Woz

Hard to describe, and I suspect different boiler manufacturers might deal with it differently.
Basically the boiler needs to know when the controller is calling for hot water, override the weather compensation and turn the boiler temp to max, and use the hot water tank thermostat to limit the temperature.
If you don't modify the wiring the hot water will only get as hot as the boiler flow temperature under weather compensation control, which might not be hot enough on a warmish day.
My kit came with the wiring details.
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Here's another update.

My gas bill for December: 166 Units without weather compensation
My gas bill for January: 170 Units, with weather compensation.

(1 unit = 100 cuft)


Am I disheartened? No, not at all. The last week of January was way below zero and the boiler ramped up accordingly. When spring eventually arrives that's when I expect to see significant savings.

Watch this space !!!!
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Here's this months update. Units are 100's cuft

December 166 units (no weather compensation 5.21 units/day average)
January 170 units (1st month with weather compensation. 5.19 units/day average)
February 163 units (short month so 5.28 units/day average)

The first week or so of February was cold and the boiler ramped up, while the second half was unseasonably warm and the boiler throttled back accordingly. Roll on summer.
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Interesting indeed. How does this compare to last year?
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Jon

Can't really compare with last year as the house renovations were a long way from being completed. Having floorboards up, ceilings down and walls missing is not conducive to saving energy.
@Oakbank

Thanks to Oakbank for starting this thread. I am not as familiar with weather compensation solutions as smart thermostats. In the UK at least they seem to be relatively rare/unknown/unpromoted.

However based on my knowledge and use of smart thermostats I thought it maybe helpful to detail how they relate to this issue.

The traditional boiler control method is/was a simple on/off control achieved by sending to the boiler a 'call for heat' signal. This causes the boiler to run at full power whilst the call for heat signal is present and then to fully turn off when it is not. This overall is a less efficient method than the newer approach which is referred to as modulated control. With modulated control the output of the boiler is varied depending on the demand and closeness to the desired heat level. Modulated control not only should achieve energy savings but help ensure a more stable temperature is achieved with less over and under shooting of the desired temperature.

It seems the weather compensation kit is causing a suitable boiler to operate in modulated mode even with a 'dumb' thermostat.

Since it is possible and arguably more common to achieve modulated control with a suitable smart thermostat this could be considered as an alternative way of achieving this and arguably has additional benefits.

In my case my boiler is located on a south facing wall with its exhaust also on that south facing wall. It would be harder to correctly fit a weather compensator since it would need shading from sunlight to avoid the temperature sensor reading being distorted. (You could fit a shield to prevent sunlight hitting it.)

A smart thermostat typically is able to obtain outdoor temperatures via an Internet service by looking up a local weather station and hence will not need to rely on your own outdoor sensor. This will therefore solve my problem.

A smart thermostat also adds the benefit of advanced scheduling and the ability to monitor the presence of occupants and therefore achieve additional energy savings. It can also link to a thermostat or even multiple thermostats and matching smart TRV valves and report to the boiler if any room needs heat. (If all rooms are reaching their desired temperature the boiler can then reduce its output.)

So whilst a weather compensator would and should be a definite improvement over the traditional call for heat method I would say a smart thermostat would be even better.

Note: There are two different but similar digital protocols which a smart thermostat can use to control a boiler to enable modulated control. There is eBUS and OpenTherm. OpenTherm was original developed by Honeywell and as its name suggests is now an open standard. eBUS is a proprietary standard - each manufacturer has their own flavour.

According to Tado a manufacturer of a smart thermostat and TRV system which supports both OpenTherm and eBUS they say eBUS is superior - mainly I believe in the area of fault monitoring of boilers.

Vaillant and Worcester Bosch only sell boilers in the UK with eBUS support.
Nest only has OpenTherm support.
Drayton Wiser only has OpenTherm support.
Most of Honeywells better smart products are US only but logically they also will only support OpenTherm.
As far as I can tell Hive and Netatmo do not support OpenTherm or eBUS.
As mentioned Tado supports both OpenTherm and eBUS - with the problem mentioned below for the newer Vaillant VR66 controller.

Due to local requirements in the Netherlands, both Vaillant and Worcester Bosch sell boilers fitted with eBUS to OpenTherm conversion modules _made by Vaillant or Worcester Bosch themselves_. However Vaillant at least will invalidate your warranty if you get and fit this genuine module in the UK.

Apparently Vaillant have also more recently changed/updated their eBUS protocol in the newer VR66 controller and not released the specs and Tado have not yet been able to reverse engineer this. The VR65 is supported by Tado.

There are some lesser known boiler brands which do have built-in OpenTherm support. See - https://myboiler.com/opentherm-capable-boilers/

The belief is that Vaillant and Worcester Bosch are using eBUS to mainly force customers in to buying their own matching compatible (semi) smart thermostats.
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"
So whilst a weather compensator would and should be a definite improvement over the traditional call for heat method I would say a smart thermostat would be even better.
"
Couldn't agree more. Thanks for your detailed explanation re. boiler controls. I acknowledge weather compensation is a 'half-way house' when it comes to boiler control and a smart thermostat offering modulating control based around a room temperature setpoint is the way forward. My boiler, a Logic Heat, is one of those listed as being OpenTherm capable. I just need to get the right smart thermostat and get it all to work.

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