Is my boiler oversized? If so, what can I do?

[Last Plumber]

Not attempting to hijack this thread was just providing some detailed information for the OP in respect of his own HLC.

116 square metres is the Total Floor Area (from the EPC)

Attached are all the dimensions and a HLC produced using the Stelrad Basic HLC available here originally - BTU Calculator | Heat Loss Calculator For Your Home - https://www.stelrad.com/advice-hub/heat-loss-programmes/

We had a bit of a go at the developer about this for a number of reasons.

1. The Lounge is the only room that feels cold during winter. The 2 radiators are installed against internal walls as the room has a large DG PVCU French Door. As already mentioned these are 600 x 600 Type 11 (K1) and would appear to be undersized for the room.
2. The upstairs heating has only been turned on 2 or 3 times in the last 2 years.
3. The developer claimed that the floor construction is "Jetfloor insulated beam & block" floors (giving a U value of 0.15W/m²K)
4. The developer also claims that 400mm of quilt insulation is installed in the loft zones (giving a U value of 0.11W/m²K).
   NB. this is beyond the building regulations in effect at the time and is actually around 270-300mm (two bats of earth wool rolled in opposite directions)
5. The First floor construction is unknown but would be whatever was required in 2018.
6. The system was designed by Ideal/Stelrad for Taylor Wimpey with a design temperature for the heating system
   80'C Flow
   60'C Return
   (there is/was a loophole in the building regulations for HEAT ONLY boilers that permitted installation at design temps outside of the condensing parameters of the boiler. This may or may not have been closed with the recent regulation changes).
7. One thing that will 100% impact any future ASHP would be the 10mm Hep2O plastic pipe that has been used in the drops to all radiators.

Octopus quoted the following

• ASHP: Daikin EDLA04E2V3
• Flow Temperature 46'C
• MCS SCOP Heating 3.65
• MCS SCOP Hot Water 2.6944999999999997
• HP System Electricity Consumption Heating: 2740 kWh (Current using Boiler: 10,000 kWh)
• HP System Electricity Consumption Hot Water: 894 kWh (Current using Boiler: 2,000 kWh)
• HP System Electricity Consumption Total: 3634 kWh (Current using Boiler: 12,000 kWh)

Our Actual energy consumption for Gas, August 2022 to August 2023, was 6500kWh.

Even using our actual consumption and adjusting the figures

• Heating: 4400 kWh @ 3.65 SCOP = 1204 kWh
• Hot Water: 2100 kWh @ 2.695 = 779 kWh
  • Plus 52 x Anti Legionella Cycles (3kWh Immersion x 250L x 10'C) = 152 kWh
  • Gives a Hot Water Total: 931 kWh
  • Total Annual Electricity = 2135 kWh

We didn't go ahead for a few reasons:

1. We were not particularly confident in the HLC carried out by them
2. The SCOP for heating looks kind of low but the 10mm Hep2O plastic pipe is likely a factor
3. The SCOP for Hot Water is terrible.
   I suspect that a better designed system, paired to a quality or custom cylinder, should improve that to 4 or more
4. Based on our consumption and those SCOPS it would cost us more per year to run an electric ASHP than it currently does using Gas in addition to the capital outlay for converting.
5. I am certain that we can improve our gas consumption by
   • Increasing the size of the radiators (so we can reduce the flow temp)
   • Adding Weather Compensation
     This has an extra benefit of decoupling our Heating and Hot Water temperatures and allowing the hot water temp to be determined by the cylinder stat. Currently both are determined by the boiler temperature setting of 64'C (cannot go lower as the hot water becomes tepid rather than hot)

It would seem that we are going to have to wait on improvements in tech or the decoupling of Gas & Electricity prices before moving to an ASHP.

I have seen Vaillant have a new, internal, Heat Pump Cylinder (fluoStore?) that was shown at the German ISH 2023 Show that has a SCOP of 5.

If you look at the heat loss attachment, it is more like I would expect. I would accept that as correct. Even though it is a tad below what I would come up with, it is close enough. There are many factors involved in heat loss calculations and you wouldn't physically notice the difference between those figures and the ones I would use.

Bedroom 1 is 2865 Btu/hr (839W).
On the initial thing you posted, bedroom 1 was 962 Btu/hr (282W). That would be too small to be a bedroom.
That's why I queried it. Your total heat loss on the attachment is 44985 Btu/hr (13.167Kw). Not the 13,753 Btu/hr (4.031 Kw) on the other sheet. I do not know the reason for this difference but the initial one is not right, or at least that is how it looks to me reading it.

Hope this helps!

 

[Desktop987456]

Our Actual energy consumption for Gas, August 2022 to August 2023, was 6500kWh.

That's not much for size of property and number of rads in the system. Out of interest, can I ask how many hours was heating on ~10hrs daily? And these figures includes heating season when system was running at full or partial load?

 

[Knappers]

I'm sorry it's been difficult reading.
Is this a combi - I thought it was.
Or a heat only - as it seems to have become.
All this technical 'headless chicken-ing' to 'help' someone who's system isn't even balanced properly.
Talk all the heatloss you like but not once have I heard anyone mention reheat time...?
Perhaps when there are perfect apliances to install then we can look at putting them in!
10:1 modulation would be great on a 12kw heat only boiler with a high input cylinder, HW priority, weather & load comp with adjustable self learning curve.

Please!
Where do I buy that?

Get it balanced, fit smart controls, keep it well maintained.