Boiler / Radiator Total BTU Advice Needed

[Pgeddon]

Hi all

Having some renovations done on ground floor and looking to get rid of / replace some of the older looking boilers on that floor (mainly Double panel, double convector, some double panel single convector.

As well as replacing these I wanted to add a couple radiators too, but have become a bit confused about the delta calculations I should be using to stay under the total KW of the boiler limit.

Ours is a Worcester Bosch 40 CDI Greenstar Conventional Central Heating Only Convecting boiler (41KW), and it powers 23 rads through the property, plus an unvented hot water cylinder.

I run the boiler on max usually, with a flow temp of around 84c, so assume this means Im T60?... So should be using this when calculating the output for any newer boilers?

Also as this is a condensing boiler with 90% efficiency, is it possible for me to run it at T50 or lower so I can make it more efficient? I've read online I can't drop the flow temp too much as the hot water tank needs to stay above 60c to avoid legionnaire's disease etc. With that in mind do I have any other options where I can make this setup more efficient? As stated above ideally id like to add more rads.

thanks

Ged

 

[Timmy D]

You really need to do heat loss valve for each room and work from there.

You also want to commission the boiler flow/return temps and rad balancing to get a even heat up of the property and more importantly ensure that the return temp is low enough for the boiler to condensate.

Sorry but I’m not explaining how to do the above, it’s too much to write. Have a google.

 

[Pgeddon]

You really need to do heat loss valve for each room and work from there.

You also want to commission the boiler flow/return temps and rad balancing to get a even heat up of the property and more importantly ensure that the return temp is low enough for the boiler to condensate.

Sorry but I’m not explaining how to do the above, it’s too much to write. Have a google.

thanks for the reply,


Rads already been balanced recently, the even heating up of the rads isn’t the primary concern, I’m more concerned about the efficiency of the system and whether I can add some more rads as part of some renovation work.

I’ll take a look at the return temps on the boiler, from reading a bit I think this one needs to be 70/50 to condensate. I’ve been running on full whack with a flow temp of 85c odd. Tried running it on 70c flow temp earlier for an hour and half or so, rads didn't seem to be massively hot. Usually has 23 rads but we've had 5 or 6 blanked off as part of the renovations so far.... so expected the ones remaining to heat up pretty quickly.

Googled heat loss valve, nothing overly relevant came up.

 

[king of pipes]

23 + radiators on a 40 kw boiler is not going to be cheap to run a unvented cylinder has a 18 kw coil so heating all these together will be expensive, a average home has 8 - 10 rads, many of my customers are paying £250 a month for their energy and live in 3-4 bed modest family homes, yours will be double that or more ? the improvements you make should include work to make your home more thermally efficient so it doesn't leak heat once a comfortable temperature is achieved and allows the boiler to modulate down to a lower kw output and top up the heat loss.
Delta T60 - T50 is the flow temperature setting which we have to design heating systems to, this allows the return temperature to be 40 ° c or below and allows the boiler to stay in condensing mode for as long as possible this will not be possible for your set up why I hear you say ??
Well you have become used to a radiator temperature setting of 80° c + and a hot water temperature of 60 °c + and it is the hardest thing for us as installer to try and educate our customers that this is not the best way to heat their homes and hot water, updated controls that adapt to our ever changing weather patterns, insulation, insulation and more insulation is what's needed walls ,floors , loft space, windows pipe work it's the only way to reduce energy costs and heat loss , the lower your boiler flow temperature the less gas you will use your radiators don't need to be scalding hot all the time and the hot water temperature can be reduced even 5 ° c will make a difference but to achieve a successful outcome you will need to invest in reducing the heat loss in your property, firstly carry out a heat loss calculation there are many online tools to do this then get yourself a Heating engineer who can guide you . Regards Kop

 

[Pgeddon]

23 + radiators on a 40 kw boiler is not going to be cheap to run a unvented cylinder has a 18 kw coil so heating all these together will be expensive, a average home has 8 - 10 rads, many of my customers are paying £250 a month for their energy and live in 3-4 bed modest family homes, yours will be double that or more ? the improvements you make should include work to make your home more thermally efficient so it doesn't leak heat once a comfortable temperature is achieved and allows the boiler to modulate down to a lower kw output and top up the heat loss.
Delta T60 - T50 is the flow temperature setting which we have to design heating systems to, this allows the return temperature to be 40 ° c or below and allows the boiler to stay in condensing mode for as long as possible this will not be possible for your set up why I hear you say ??
Well you have become used to a radiator temperature setting of 80° c + and a hot water temperature of 60 °c + and it is the hardest thing for us as installer to try and educate our customers that this is not the best way to heat their homes and hot water, updated controls that adapt to our ever changing weather patterns, insulation, insulation and more insulation is what's needed walls ,floors , loft space, windows pipe work it's the only way to reduce energy costs and heat loss , the lower your boiler flow temperature the less gas you will use your radiators don't need to be scalding hot all the time and the hot water temperature can be reduced even 5 ° c will make a difference but to achieve a successful outcome you will need to invest in reducing the heat loss in your property, firstly carry out a heat loss calculation there are many online tools to do this then get yourself a Heating engineer who can guide you . Regards Kop

Yeah it's not been the cheapest to run unfortunately. December was maybe £900 gas/electricity for that month. But it was particularly cold. November/Jan maybe around half that.

Thanks for the detailed reply, I am in the process of making the property more efficient, it only had 100mm loft insulation for some parts, 200mm in others, and none at all in maybe 1/4 of the loft space. I've topped all that up to 300mm and 400mm in some cases. Also none of the pipes that ran in the cold spaces were lagged. So have been lagging those where appropriate too, maybe 50M in total, perhaps slightly more. And lastly it's a suspended floor which im insulating with 200mm wool too. I am seeing an improvement here. So with insulation sort of in hand, im still interested in the best way to run the boiler.

Is there an easy way I can see the return temperature on a Worcester Bosch Greenstar 40CDI Conventional? It'd be good to know what it's running at.

A few calculators id used online for total radiator demand said add 3kw on for the hot water tank, Im assuming that calculation is for vented cylinders then? As you're saying my cylinder is taking 18kw?! I guess that would explain why the radiators dont go very hot when we've got the central heating + hot water on at the same time.

Perhaps my property needs subdividng into more central heating zones? and do you think perhaps it would be worth changing to a different system than a conventional with unvented cylinder?

 

[Enthalpy]

Is there an easy way I can see the return temperature on a Worcester Bosch Greenstar 40CDI Conventional? It'd be good to know what it's running at.

I use cheap aquarium thermometers on the boiler flow and return. Knot the wire round the pipe and fix the sensor to the pipe with a small cable tie. You can add a bit of heat sink compound or Vaseline for good measure and cover with pipe insulation.

 

[king of pipes]

It seems your well on the way to getting the insulation done which is good , regarding your system if it could be divided up in zones then there could be further savings by timing the on and off times and have lower temperatures so your not heating rooms when it's not needed , check if your boiler is modern enough to use weather compensation ? Worcester Bosch have their own control for this although other maybe compatible, Honeywell Evo home could be worth considering? you need to keep your heating flow temperature low as possible ideally 65 ° c or lower if possible any higher then the boiler will most certainly not condense as much as it could clamp on thermometers are available and will give you a good idea of the temperatures .
Regards Kop

 

[Pgeddon]

I use cheap aquarium thermometers on the boiler flow and return. Knot the wire round the pipe and fix the sensor to the pipe with a small cable tie. You can add a bit of heat sink compound or Vaseline for good measure and cover with pipe insulation.

thanks, i've ordered a pair of these. Will report back the temps at the various loads.

 

[Pgeddon]

It seems your well on the way to getting the insulation done which is good , regarding your system if it could be divided up in zones then there could be further savings by timing the on and off times and have lower temperatures so your not heating rooms when it's not needed , check if your boiler is modern enough to use weather compensation ? Worcester Bosch have their own control for this although other maybe compatible, Honeywell Evo home could be worth considering? you need to keep your heating flow temperature low as possible ideally 65 ° c or lower if possible any higher then the boiler will most certainly not condense as much as it could clamp on thermometers are available and will give you a good idea of the temperatures .
Regards Kop

Yeah I'd like it to be at 65c too for the obvious benefits, though i think if we hadn't had it cranked to MAX over the cold winter the house would've been difficult to live in. I feel in a bit of a catch22 with it as even with the boiler on MAX and run often the house still wasn't warm, despite the complete lack of efficiency in operating this way.... though as you say its good that the insulation is happening and in hand, hopefully that does make a notable difference. (mostly 400mm wool in the loft floor now).

RE: zones, I have a potentially silly question, apologies if it is, but is the below correct?

:-If the property was split into 2 zones, for simplicity of maths lets say of the 24 rads...
Zone 1 = 12 rads,
Zone 2 = the other 12 rads.

If I cranked the boiler to MAX but only had Zone 1 ON, Would that cost me less £ per hour to run the boiler Vs how its setup currently with no zoning? as it'd be feeding fewer radiators?.... or does the boiler just cost the same to run per hour regardless? (again sorry if this is a silly question)

 

[gmartine]

With regards to zoning or further controls I'm assuming not every rad equates to a room but do they all need to be fully heated? At least consider fitting TRV's and or smart thermostats, whether just by heating zone valve 1 or rads with low set TRV's you will use less gas as the boiler will trim down due to less demand.

 

[Pgeddon]

With regards to zoning or further controls I'm assuming not every rad equates to a room but do they all need to be fully heated? At least consider fitting TRV's and or smart thermostats, whether just by heating zone valve 1 or rads with low set TRV's you will use less gas as the boiler will trim down due to less demand.

Yes that's the point I was eventually getting to - Ultimately if I had an engineer come do some invasive work to access the pipes and separate the downstairs (Zone1) and Upstairs (Zone2).

By only having Zone 1 ON.....is that basically exactly the same as having 12 of the radiators turned off at their TRV's?

...And either of those would automatically mean the boiler is working less hard and using less KW per hour, despite it being cranked to max? Likewise as we've currently got 7 radiators blanked off....should that be costing us less per hour by the same logic?

 

[gmartine]

If you're only trying to heat half the number of radiators by zoning you will naturally use less gas than you would by trying to heat all of them.

TRV's are either manual or smart and are a means of controlling individual room temperature. Your radiators will already have a means of closing them by using the valve (lock shield) at either end which I assume you have used to blank some of them off.

Setting the boiler to MAX set's the flow temperature to maximum however the lower the temperature you can run the boiler the more efficient it is and the less gas you will use as long as demand from your radiators can also be met.

 

[king of pipes]

Yeah I'd like it to be at 65c too for the obvious benefits, though i think if we hadn't had it cranked to MAX over the cold winter the house would've been difficult to live in. I feel in a bit of a catch22 with it as even with the boiler on MAX and run often the house still wasn't warm, despite the complete lack of efficiency in operating this way.... though as you say its good that the insulation is happening and in hand, hopefully that does make a notable difference. (mostly 400mm wool in the loft floor now).

RE: zones, I have a potentially silly question, apologies if it is, but is the below correct?

:-If the property was split into 2 zones, for simplicity of maths lets say of the 24 rads...
Zone 1 = 12 rads,
Zone 2 = the other 12 rads.

If I cranked the boiler to MAX but only had Zone 1 ON, Would that cost me less £ per hour to run the boiler Vs how its setup currently with no zoning? as it'd be feeding fewer radiators?.... or does the boiler just cost the same to run per hour regardless? (again sorry if this is a silly question)

Basically yes you will be heating fewer radiators and controling the temperature of each zone, if Trv valves are fitted then they can be controlled individually aswell unoccupied rooms or rooms which are use less can be kept on a minimum setting .

 

[Pgeddon]

If you're only trying to heat half the number of radiators by zoning you will naturally use less gas than you would by trying to heat all of them.

TRV's are either manual or smart and are a means of controlling individual room temperature. Your radiators will already have a means of closing them by using the valve (lock shield) at either end which I assume you have used to blank some of them off.

Setting the boiler to MAX set's the flow temperature to maximum however the lower the temperature you can run the boiler the more efficient it is and the less gas you will use as long as demand from your radiators can also be met.

Basically yes you will be heating fewer radiators and controling the temperature of each zone, if Trv valves are fitted then they can be controlled individually aswell unoccupied rooms or rooms which are use less can be kept on a minimum setting .

Yes, thanks - that's what I assumed..... but what i've monitored today didn't quite add up to that so left a little confused.

Early January I did a quick measure of how many M3 of gas we were using per hour when I put the Central heating on...back then the CH on for one hour was using about 3.5M3 per hour (38.5kw/hr -ish?)..... between then and now we've blanked off 5 radiators, but I measured it today and we're still using about 3.1M3per hour (33kw/hr-ish?).

With a good 25% of the rads now not in the circuit i'd have expected it to drop much further? Could this mean there's a problem somewhere or does this amount of difference seem normal to you guys?

I ask because my proposed zoning would be essentially to eliminate 12 out of each zone, so i'd hoped that when using either zone it'd roughly half the amount of M3 my boiler would be using, and halfing the cost per hour to run it?

What have I missed? haha

 

[king of pipes]

Your missing the fact that when all the rads were working your home would heat more quickly and switch off sooner but more rads heating equates to more gas used
Take away 25% of the radiator output then your boiler will struggle to heat your home to a comfortable temperature so be on longer your compensating by running it at a higher temperature and probably still not achieving the comfort level you require? this will use more gas
You will not see savings until your work is completed as I said unless you invest and are able to heat the property and hold that temperature you may not see a saving at all ? the boiler needs to run for a shorter lengths of time and or at lower temperatures zoning and adding more control of individual areas and rooms will see savings but , insulation, draught proofing, heavy lined curtains , keeping doors closed anything that uses power switch off changing the habits of a life time really, you could get a energy performance inspection done this will give you a good idea of how efficient your home is and what improvements could be made to use less energy and get you savings it not that expensive under £100 in most cases . Regards Kop

 

[gmartine]

Also, despite closing seven radiators there's no indication of their output, room size and therefore heatloss as a proportion of the rest of house so loss comparisons won't necessarily be as proportional as you expect. Every improvement suggested will help but if you really want to accurately drill down into your gas use metrics then a smart TRV based system maybe the way to go.

 

[gmartine]

Also, despite closing seven radiators there's no indication of their output, room size and therefore heatloss as a proportion of the rest of house so loss comparisons won't necessarily be as proportional as you expect. Every improvement suggested will help but if you really want to accurately drill down into your gas use metrics then a smart TRV based system maybe the way to go.