Conventional (compact) boiler replacement: suggestions/advice pls.

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As I stated in my thread starter.."all replies gratefully received." (y)

The Vokera Vision Plus 20 S (Obviously you can substitute an alternative brand for comparison).

740 x 420 x 275 (the boiler connections are at the bottom so you’ll have to run them down the side if they’re from above as the spacer kit may bring it past 300mm).

Stainless heat exchanger serviced from front

19kW to 3.41kW

Personally I have that running with the EPH ember system, two heating zones and priority domestic hot water all on OpenTherm and controlled by app in a property I let. The thermostats are not the prettiest but they work. An external sensor can be fitted too if you wish to factor in weather conditions (I would).

If you run it with existing ON/OFF controls the efficiency % hit would be around 3-4%

Range rating is easy push button but better if the installer does it.

Hard to quantify ‘whisper quiet’ judgements but the sound power is 50db and obviously less if range rated. Your Baxi should have an energy label to show its sound power. All manufacturers should give you this on the energy label.

As an example to compare roughly to your daughters house a four bed 10 year old 1 bath, 1 en-suite I did a heat loss for came in at 9.4kW when -5 degrees and 5.05kW at +10 degrees. An 90 year old 4 bed detached 15.65kW at -5 degrees and 7.87kW at +10 degrees. These losses will be quite a bit lower when controlled with good controls as the house will be kept at a thermal equilibrium. I find it useful to mention losses in milder weather as that gives a reference to modulation rather than just quoting 1:5 or whatever.

18,000kWhrs/annum equates to roughly £810 @4p/kW NG so every % saved is £8.10p
 
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I wonder if an heat loss calculator, might work even better, if there was some input from present actual annual consumption? I ran through the above calculator for my home - It came up with an annual Kwh some 20% higher than we actually used, with just the boiler, gas hob and double gas oven consuming gas - so the 20% high would be even more.
No, it wouldn't. Heat loss is heat loss and is not affected by usage patterns. You need the correct power to overcome the losses in the building and heat the home. Usage patterns will increase or reduce gas consumption, but heat loss is a constant. The energy usage figure given is used in MCS calculations to determine renewable heat incentive payments, it's got nothing to do with what power boiler is required
 
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That is in dispute,

The constructional design of the air intake, fan, burner, combustion chamber, heat exchanger surface and flue will be optimised for one rate of burning. When a boiler is burning at a rate that is either lower or higher than the rate for which the construction was optimised then the boiler will not be as efficient as it is at the designed rate of burning.
Got any evidence for that Bernard, or is this just another one of your ramblings?
 
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No, it wouldn't. Heat loss is heat loss and is not affected by usage patterns. You need the correct power to overcome the losses in the building and heat the home. Usage patterns will increase or reduce gas consumption, but heat loss is a constant. The energy usage figure given is used in MCS calculations to determine renewable heat incentive payments, it's got nothing to do with what power boiler is required

I see your point, but as said it predicted much higher consumption than our actual, despite our heating being on almost 24/7.
 
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A much steadier temperature in the home. No wide excursions in temperature because the boiler has reached temperature and shut down. I have a modern Vaillant to which I added the Vaillant Ebus control system with outdoor sensor. Which means it can precisely match the demand for heat, without having to run flat out then off, then flat out again as the house cools down. It knows what the temperature is, knows what temperature you have set, brings it to the temperature and as it nears it, ramps itself gradually down so it doesn't overshoot, then just gently maintains that temperature.

We used to know when the old boiler fired up, by the creaking of the pipes as they expanded. That no longer happens, because the boiler can just tick-over gently, working at maximum efficiency. We can no longer tell how cold it is outside, by how often the creaking begins, we can only tell by either looking at the outdoor temperature, or feeling how warm the radiators are.
Thanks so much for that, Harry;...that really appeals.(y)

I mentioned a Vaillant ecoTEC Plus 415 ErP upthread,...would that suit our requirements?...and if so, and if at all possible, could you recommend which actual controls to buy.
 
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Got any evidence for that Bernard, or is this just another one of your ramblings?

Not a ramble, it is an opinion based on some basic rules of fluid dynamics, If the passage for hot combustion gases along/through the heat exchanger is a comfortable fit for those gases at full power ( maximum contact between gas and metal ) then it will be a loose fit for the reduced volume of gases when the boiler is running at minimum power.

It is also the opinion of a person whose career was designing boilers and heat exchangers. He designed some gas to water heaters with variable geometry ( such as altering the shape of the combustion chamber ) to maintain efficiency over the full range of the heaters power output.

No I do not have any documented results of trials that were conducted, only verbal comments.
 
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The Vokera Vision Plus 20 S (Obviously you can substitute an alternative brand for comparison).

740 x 420 x 275 (the boiler connections are at the bottom so you’ll have to run them down the side if they’re from above as the spacer kit may bring it past 300mm).

Stainless heat exchanger serviced from front

19kW to 3.41kW

Personally I have that running with the EPH ember system, two heating zones and priority domestic hot water all on OpenTherm and controlled by app in a property I let. The thermostats are not the prettiest but they work. An external sensor can be fitted too if you wish to factor in weather conditions (I would).

If you run it with existing ON/OFF controls the efficiency % hit would be around 3-4%

Range rating is easy push button but better if the installer does it.

Hard to quantify ‘whisper quiet’ judgements but the sound power is 50db and obviously less if range rated. Your Baxi should have an energy label to show its sound power. All manufacturers should give you this on the energy label.

As an example to compare roughly to your daughters house a four bed 10 year old 1 bath, 1 en-suite I did a heat loss for came in at 9.4kW when -5 degrees and 5.05kW at +10 degrees. An 90 year old 4 bed detached 15.65kW at -5 degrees and 7.87kW at +10 degrees. These losses will be quite a bit lower when controlled with good controls as the house will be kept at a thermal equilibrium. I find it useful to mention losses in milder weather as that gives a reference to modulation rather than just quoting 1:5 or whatever.

18,000kWhrs/annum equates to roughly £810 @4p/kW NG so every % saved is £8.10p

Thanks for that,...very much appreciated. I’ve only skimmed the surface of what is out there but to my untrained eye the bang to buck ratio for Vokera boilers appears to be exceptionally good. (y)

p.s. My Baxi424 manual states: “Sound power level, indoors 37dB”
 
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Thanks so much for that, Harry;...that really appeals.(y)

I mentioned a Vaillant ecoTEC Plus 415 ErP upthread,...would that suit our requirements?...and if so, and if at all possible, could you recommend which actual controls to buy.

I'm not an heating engineer, I'm just relating my own experience.

My system is -

Ecofit Pure open vented boiler heat only

VR65 E-Bus Control centre

VR10 HW cylinder temperature sensor

VRC 470f Display / control

VR21 Wireless outdoor temperature sensor

SDM 1901 3-port valve

It uses the wireless version of the controls, but I think they will be obsolete now.
 
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That is in dispute,

The constructional design of the air intake, fan, burner, combustion chamber, heat exchanger surface and flue will be optimised for one rate of burning. When a boiler is burning at a rate that is either lower or higher than the rate for which the construction was optimised then the boiler will not be as efficient as it is at the designed rate of burning.

I agree with that. I’ve noticed in several recent threads references to need for a large turndown ratio, even to the extent of implying the system won’t work properly without. I’m sceptical and don’t think it makes more than a marginal improvement, or as per your post, might be worse. My system is 22 years old with on/off control, and AFAIK modulation wasn’t an option till more recently. It’s W-plan with fairly typical ratio of rad area/boiler output, and in CH mode it never reaches control-stat setting (70-75°C), so it wouldn’t modulate even if it were that type. No noticeable variation of room temperature. The boiler only reaches control-stat setting in HW mode, when it cycles 2-3 times before the cylinder stat is satisfied.
 
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Thanks for that,...very much appreciated. I’ve only skimmed the surface of what is out there but to my untrained eye the bang to buck ratio for Vokera boilers appears to be exceptionally good. (y)

p.s. My Baxi424 manual states: “Sound power level, indoors 37dB”

As the sound power is measured on a logarithmic scale the Baxi is a lot quieter than the Vision Plus although we've not had any comment over noise.
 
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I agree with that. I’ve noticed in several recent threads references to need for a large turndown ratio, even to the extent of implying the system won’t work properly without. I’m sceptical and don’t think it makes more than a marginal improvement, or as per your post, might be worse. My system is 22 years old with on/off control, and AFAIK modulation wasn’t an option till more recently. It’s W-plan with fairly typical ratio of rad area/boiler output, and in CH mode it never reaches control-stat setting (70-75°C), so it wouldn’t modulate even if it were that type. No noticeable variation of room temperature. The boiler only reaches control-stat setting in HW mode, when it cycles 2-3 times before the cylinder stat is satisfied.

i think you have misunderstood,

modern boiler are designed to be optimal across the range, however they will be most optimal when cruising at a low modulation (similar to driving your car at 55mph for optimal fuel consumption).

modern boilers are ecu controlled, again similar to a car, where for a given amount of air and comparing inlet and outlet temperatures etc etc it optimises the gas valve.

it is proven that using modern low temperature heating with controls such as opentherm or the boiler manufacturers equivalent does improve gas consumption, albeit only a few percent in some instances but can be as much as 25% in others, and therefore not a big deal on its own, but if everyone in the country done that it would be a massive deal.
 
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Well spotted!...thank you.

It’s the Vaillant ecoFIT pure 418 Regular that I meant to link to;...that’s the range which is ‘cupboard fit’...29.5cm depth.

https://www.plumbnation.co.uk/site/vaillant-ecofit-pure-418-regular-boiler-natural-gas-erp/

Check, check and check again!...that’s what I failed miserably to do. :notworthy:

Not that I’d ever consider unilaterally ordering a boiler myself of course.
I have the EcoTEC plus 418 and when I was buying it, I asked what the difference was between the Ecotec Plus and the Ecofit pure (which was cheaper) and I was told that the pure was just a rebadged Gloworm.
 

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