Going green(er) with a Viessmann 200W (& heating efficiency home improvements)

Alnat1

So, over a pretty mild winter, you are stating your new boiler (plus insulation, underfloor system, new radiators etc.) has saved you around £300.

How many years until you get ROI?

Screwdriva

Alnat1 said:

So, over a pretty mild winter, you are stating your new boiler (plus insulation, underfloor system, new radiators etc.) has saved you around £300.

How many years until you get ROI?

Over 4 months of a less mild winter (compared to the previous year) we saved £340. Over the full year, we expect to reduce consumption by quite a bit more (forecasted ~11K kWh for this year). These saving will also come from the boiler's cylinder thermostat controls (50 degree DHW temperature) with a weekly legionella cycle. 

So to answer your question, best guess is a 3-4 year ROI on the boiler's installed price of £3500. UFH was a long overdue improvement and no new radiators were purchased, just relocated. Then there is the halving of the emissions, which was quite important to us as well. 

Reed_Richards

Screwdriva said:

Reed_Richards said:

But if the old boiler was

Screwdriva said:

... running at ~80-85% efficiency... 

then it's not possible to achieve a 30% improvement!  

Sure it is. The lowest the Greenstar could modulate was 6kW. The lowest the Viessmann can modulate is 2.1 kW. Lower output = less gas burnt at a higher efficiency. To highlight my point, even on the coldest day this winter (-5 C), the V200 never exceeded ~ 5kW heat output.

This should help the benefits of increased modulation:

https://www.heatgeek.com/what-is-boiler-modulation/

I know you think your new Viessman boiler is the best thing since sliced bread and quite possibly it is but if you achieved a 30% saving in gas usage that means your old boiler wasn't nearly as efficient as it was supposed to be.  Lets say your new boiler manages a spectacular 99% efficiency.  99/(10345/7102) = 68.0% average efficiency for your old boiler.  That's just mathematics.  If your new boiler isn't quite as good as 99% efficient that means your old boiler was even worse.  

I've read the Heat Geek article (and others) and I can't see anything there to indicate that you should expect anything like that difference between your old condensing boiler and your new low temperature condensing boiler.  If your old boiler couldn't achieve the same modulation range as the new one then it might short cycle but the worst case considered by Heat Geek is a 10 second cycle and even that only drops the efficiency by 12%.  And surely you would  notice 10 second cycles if you ever looked to see what your old boiler was doing.

I sense that you feel it is wrong to look a gift horse in the mouth but surely the truth of the matter is that your old boiler must have been faulty and running with an over-rich gas to air mixture for your new boiler to be that much better? 

    

Alnat1

I don't think you can simply dismiss all the other changes you made to your heating/hot water system and controls as "long overdue" and therefore not to be included when you calculate ROI. The total cost of all changes have to be included.

Up here we'd say - tha's meking thi sen look daft.

Screwdriva

Alnat1 said:

I don't think you can simply dismiss all the other changes you made to your heating/hot water system and controls as "long overdue" and therefore not to be included when you calculate ROI. The total cost of all changes have to be included.

Up here we'd say - tha's meking thi sen look daft.

I don't factor in underfloor heating installation costs into my ROI calculations for the boiler. Keeps things nice and straightforward, especially as some may have it installed already.

Down here, I'm not sure what we'd say to that?!?

Reed_Richards said:

I know you think your new Viessman boiler is the best thing since sliced bread and quite possibly it is but if you achieved a 30% saving in gas usage that means your old boiler wasn't nearly as efficient as it was supposed to be.  Lets say your new boiler manages a spectacular 99% efficiency.  99/(10345/7102) = 68.0% average efficiency for your old boiler.  That's just mathematics.  If your new boiler isn't quite as good as 99% efficient that means your old boiler was even worse.  I've read the Heat Geek article (and others) and I can't see anything there to indicate that you should expect anything like that difference between your old condensing boiler and your new low temperature condensing boiler.  If your old boiler couldn't achieve the same modulation range as the new one then it might short cycle but the worst case considered by Heat Geek is a 10 second cycle and even that only drops the efficiency by 12%.  And surely you would  notice 10 second cycles if you ever looked to see what your old boiler was doing.I sense that you feel it is wrong to look a gift horse in the mouth but surely the truth of the matter is that your old boiler must have been faulty and running with an over-rich gas to air mixture for your new boiler to be that much better? 

It's extremely unlikely the old Bosch boiler was faulty as it was serviced and checked annually. It did cycle often but nowhere near every 10 seconds. The Viessmann has not cycled once.

As far as sliced bread goes, the numbers should highlight it's a great alternative for those who cannot get a heat pump for whatever reason....but I don't sit around admiring it....mostly. 

Alnat1

Screwdriva said:

I don't factor in underfloor heating installation costs into my ROI calculations for the boiler. By your logic, I would need to factor in costs for our triple glazed windows, loft insulation and the host of other measures we've taken to reduce property heat loss.  

The underfloor is part of the heating system and of course the cost has to be included in the calculations.

It's like me trying to claim my battery storage has saved me £2500 in energy costs in a year and therefore paid for itself and it's installation but not including the cost of the panels in the calculation 

Screwdriva

Alnat1 said:

It's like me trying to claim my battery storage has saved me £2500 in energy costs in a year and therefore paid for itself and it's installation but not including the cost of the panels in the calculation 

Not to sound cheeky, but I'm confident we would have achieved a near identical result with oversized T23 radiators on the ground floor in lieu of UFH. This was confirmed by the installer who suggested this as a less costly course of action. (We insisted on UFH as we wanted the white tiles and prefer the feeling UFH delivers). Both circuits run at a very similar flow temperatures (5 degrees lower flow for the UFH). 

To suggest that the above results are somehow dependent on UFH misses the point. That said, we've both made our points clear so probably best to leave it there. 

70sbudgie

My head is a bit fuzzy at the moment, so sorry if this is a daft question...

I think you are implying that the improved modulation is the reason for the fantastic savings. Doesn't this suggest that both boilers, old and new, were massively oversized? And the new one perhaps slightly less so? Does you new boiler ever output its max rating - or close to it? What savings could be achieved simply by correctly sizing the boiler?

paul991

Roughly what does it cost to install underfloor heating per square meter in a existing concrete floor?

70sbudgie

paul991 said:

Roughly what does it cost to install underfloor heating per square meter in a existing concrete floor?

You either need to dig up the existing slab or raise the floor level by laying a new one on top. The cost will be down to which method you use, more than the ufh itself.