From £1,166/Year to £636/Year: Our Complete Home Efficiency Journey

The Starting Point: January 2021

January 2021. New house. 1970s 4-bed detached. The first winter revealed what we'd inherited: a house that "wasn't great at heating up."

What We Inherited

• 50mm loft insulation - well under modern regulations
• Original double-glazed windows from the 1970s - very old versions, some replaced, most original
• Old T1/T2 radiators - no TRVs, no convector fins
• Potterton Netaheat 16/22kW boiler - 1975-1988 vintage, 65% efficiency
• Truwel pipework - from the 1970s copper shortage era

The first winter was telling, with rooms that took forever to warm up and a landing that remained persistently cold. The kitchen was freezing in the mornings, and it became clear that heat was escaping faster than the system could replace it.

Year 1 Baseline (Post-Loft Insulation)

We immediately tackled loft insulation in January 2021 (50mm → 350mm). This established our baseline:

• Period: Jan 22, 2021 → Jan 21, 2022
• Total consumption: 18,539 kWh/year
• Estimated cost @ 6.29p/kWh: £1,166.12/year
• Winter months: 84-93 kWh/day
• Summer months: 11-13 kWh/day

This became the baseline for all future improvements, with everything we did subsequently measured against Year 1 to understand the true impact of each change.

The Complete Timeline: What We Did and When

Over the course of five years, we completed four major improvement phases, with strategic sequencing guiding our decisions throughout the journey.

2021: Foundation Year

• January: Loft Insulation Phase 1 - £598.09
  • 50mm → 350mm total depth
  • DIY installation, Wickes trade account
  • Perimeter and end sections
  • Foundation for everything else

2022: Windows and Radiators

• January: Windows Round 1 - £2,376
  • Living room, guest bedroom
  • Start of window replacement program
• March: Front Door - £1,212
  • Improved insulation and draught-proofing
• November: Loft Insulation Phase 2 (started)
  • Central boarding section
  • Electrical overhaul (completed Oct 2023)
• November: Windows Round 2 - £1,800
  • Office, bathroom, landing
• December: Radiators + Pipework - £2,406.48
  • 10 radiators replaced (T11/T21/T22 with convectors and TRVs)
  • All copper pipework (replaced Truwel)
  • Strategic oversizing for 50°C flow temps
  • £682.03 radiators, £1,530 labor, £170.20 gas valve, £24.25 Sentinel

2023: Living With Improvements

• Throughout year: Monitoring consumption
  • Year 3 consumption: 12,562 kWh/year (32.2% reduction vs Year 1)
  • Validated radiator + window impact

2024: Boiler Upgrade and Optimization

• January: Boiler Upgrade - £3,180
  • Vaillant Ecotech Plus 826 (26kW)
  • Weather compensation controls (self-sourced £294.53)
  • 7-year warranty extension
  • 2-day installation
• Throughout year: Heat curve optimization
  • Iterative adjustment from manufacturer defaults
  • Final setting: 1.13 steepness (aggressive for oversized radiators)
  • Flow temps: 30-50°C range (vs 60-70°C typical)

2025: Fine-Tuning

• Ongoing: Monitoring and adjustment
  • myVAILLANT app issue (keeps auto-changing heat curve)
  • Regular verification and adjustment
  • Most recent 12 months: 10,115 kWh/year (45.4% reduction vs Year 1)

Year by Year: The Actual Numbers

We tracked real consumption data across five years, with no estimates or approximations to cloud the picture.

Year 1 (2021): Post-Loft, Baseline

• Consumption: 18,539 kWh/year
• Daily average: 50.79 kWh/day
• Cost @ 6.29p/kWh: £1,166.12/year
• Winter: 84-93 kWh/day
• Summer: 11-13 kWh/day

Improvements this year: Loft insulation Phase 1 was the only improvement completed, and this established our baseline for measuring all future changes.

Year 2 (2022): Windows + Radiators

• Data gap: Meter change Feb-Aug 2022, limited data
• Partial year consumption: 5,540 kWh (Sept-Dec only)
• Winter ramp-up (Dec): 112.14 kWh/day (similar to Year 1)

Improvements this year: Windows Round 1 (Jan), Front door (March), Loft Phase 2 started (Nov), Windows Round 2 (Nov), Radiators + TRVs (Dec - late in year)

Impact: Cannot calculate full year due to data gap.

Year 3 (2023): Post-Radiators, Pre-Boiler

• Consumption: 12,562 kWh/year
• Daily average: 34.41 kWh/day
• Cost @ 6.29p/kWh: £790.13/year
• Winter: 59-73 kWh/day
• Summer: 5-6 kWh/day

Improvement vs Year 1:

• Reduction: 5,977 kWh/year (32.2% reduction)
• Cost saving: £376/year
• Attribution: Windows + doors + radiators + TRVs (can't isolate)

Year 4 (2024): Post-Boiler, First Year

• Boiler installed: Jan 16-19, 2024
• Jan 2024 - Jan 2025: 10,505 kWh/year (371 days)
• Daily average: 28.32 kWh/day
• Cost @ 6.29p/kWh: £660.76/year

Improvement vs Year 3:

• Reduction: 2,057 kWh/year (16.4% reduction)
• Cost saving: £129.37/year
• Attribution: Boiler upgrade (clear)

Year 5 (2024-2025): Most Recent 12 Months

• Jul 2024 - Jul 2025: 10,115 kWh/year
• Daily average: 27.72 kWh/day
• Cost @ 6.29p/kWh: £636.26/year

Improvement vs Year 1:

• Total reduction: 8,424 kWh/year (45.4% reduction)
• Annual cost saving: £529.86/year
• Winter: 63-71 kWh/day (vs 84-93 in Year 1)
• Summer: 3.1-3.8 kWh/day (vs 11-13 in Year 1)

What Worked: The Winners

1. Loft Insulation (£598) - FOUNDATION ⭐⭐⭐

• Cheapest improvement
• Enabled all others to work better
• Strategic sequencing validated
• "Retain heat before adding heat"
• Can't isolate savings, but foundation critical

2. Radiators + TRVs (£2,406) - GAME CHANGER ⭐⭐⭐

• T11/T21/T22 with convector fins (vs old T1/T2)
• TRVs = individual room control (huge)
• Oversized for 50°C flow temps
• Enabled boiler right-sizing
• Part of 32.2% reduction Year 1→3

3. Boiler + Weather Compensation (£3,475) - EFFICIENCY OPTIMIZER ⭐⭐⭐

• Right-sized (826/26kW vs 32-36kW recommendations)
• Excellent modulation (2.5kW minimum)
• Weather compensation + heat curve optimization
• 21% heating efficiency improvement
• Clear 16.4% reduction Year 3→4 (despite more DHW usage)

4. Windows + Doors (£7,164) - NECESSARY BUT EXPENSIVE ⭐⭐

• Significant comfort improvement
• Sound reduction noticeable
• Draught elimination
• Part of 32.2% reduction Year 1→3
• But: Expensive, long payback
• Can't isolate savings from radiators

What Didn't Work: The Lessons

1. Phased Window Replacement

• What happened: 3 phases (Jan, March, Nov 2022)
• Why: Budget constraints, baby due May 2022
• Cost: Paid £189 more for same window size due to inflation
• Lesson: All at once would have saved money (but wasn't possible)
• Verdict: Accept budget reality, phasing better than not doing it

2. Initial Electrical Tidying (Loft)

• What happened: January 2021, bought junction boxes to tidy up
• Why: Didn't realize full overhaul needed
• Outcome: Had to redo with maintenance-free boxes October 2023
• Lesson: Do electrical overhaul properly FIRST
• Verdict: Wasted effort, should have planned better

3. Radiator Installation Timing

• What happened: December 2022, Christmas approaching, family stress
• Why: Fitted into plumber availability
• Outcome: Cold house, Christmas pressure, wet vac disaster
• Lesson: Winter heating work needs better timing
• Verdict: Schedule disruptive work better

4. Heat Curve App Issue

• What happened: myVAILLANT app keeps auto-changing heat curve (1.13 → 1.39)
• Why: App bug or "learning" algorithm overriding manual settings
• Ongoing: Have to check and reset regularly
• Lesson: Technology not always reliable, need manual verification
• Verdict: Frustrating but manageable, still worth it

5. Kitchen Radiator NOT Replaced

• What happened: Left old T21 under tiled floor
• Why: Budget + future kitchen reno planned
• Outcome: Kitchen colder in mornings (boiler efficient = no waste heat)
• Lesson: Accept temporary inconveniences for strategic sequencing
• Verdict: Right decision (don't do work twice)

The ROI Reality: Payback Timeline

Total Investment: £13,149.07
Annual Savings: £529.86/year @ 6.29p/kWh

Simple Payback: 24.8 years (total investment / annual savings)

BUT - This Is Misleading

1. Energy Prices Volatile

• Analysis uses 6.29p/kWh (Oct-Dec 2025 rate)
• Recent history: 3-10p/kWh range
• Higher prices = faster payback
• At 10p/kWh: £842/year savings = 15.6 year payback

2. Some Work Was Necessary Anyway

• Windows: Old 1970s double-glazing failing
• Boiler: Potterton gas valve failed (temporary fix)
• Radiators: Dated, no TRVs, inefficient
• Incremental cost matters more than total cost

3. Phased Investment Easier

• Not £13,149 upfront
• Spread over 3-4 years
• Manageable with cashflow
• Each improvement funded by previous savings

4. Non-Financial Benefits

• Comfort improvement (huge)
• No more cold spots (landing was freezing)
• Individual room control (TRVs game-changer)
• Sound reduction (windows)
• Modern aesthetic (new radiators, controls)
• Peace of mind (new boiler, 7-year warranty)
• Radiators safe to touch (not 75°C+ dangerous temps)

5. Property Value

• EPC rating improvement (estimated 1-2 bands)
• Modern heating system
• New windows and doors
• Increased marketability
• Estimated value impact: £5,000-£10,000

The truth is that ROI calculations oversimplify the reality, because factors like comfort, reliability, and strategic sequencing matter far more than what the spreadsheet shows for simple payback calculations.

The Strategic Sequencing: Why Order Mattered

The Actual Sequence

1. Loft insulation (Jan 2021) - £598
2. Windows + doors (2022) - £7,164
3. Radiators + pipework (Dec 2022) - £2,406
4. Boiler + controls (Jan 2024) - £3,475

Why This Order Worked

Loft First

• Cheapest improvement
• Highest impact per £ spent
• Foundation for everything else
• "Retain heat before adding heat"
• Without this, everything else works harder

Windows During 2022

• Phased for budget (reality)
• Before final boiler sizing decision
• Reduced heat loss = smaller boiler acceptable
• Comfort improvement while living through work

Radiators Before Boiler

• Strategic oversizing for 50°C flow temps
• Enabled 26kW choice (vs 32-36kW recommendations)
• New pipework for sealed system
• TRVs installed = room control
• Foundation for weather compensation

Boiler Last

• Sized correctly for actual need (after improvements)
• 826 works BECAUSE radiators oversized
• Weather compensation works BECAUSE house insulated
• Optimization possible BECAUSE foundation solid

What If Different Order?

Boiler First (Common Approach)

• Would have oversized (32-36kW) for poor insulation
• Poor modulation (4.5kW minimum vs 2.5kW)
• Still losing heat through roof/windows
• Radiators still inefficient (no convectors)
• Miss optimization opportunity
• Spend more, achieve less

What I'd Do Differently

Changes I'd Make

1. Electrical Overhaul First - Do maintenance-free junction boxes from start (Oct 2023). Not initial tidying (Jan 2021) then redo. Save time and effort. One disruption instead of two.
2. All Windows At Once - Budget permitting (wasn't possible). Saved £189 inflation cost. One disruption instead of three. But: Accept budget reality.
3. Better Radiator Installation Timing - Not December approaching Christmas. Summer/autumn for cold house tolerance. Less family stress. Better planning around family/holiday schedule.
4. Document Heat Curve Settings Better - Keep manual log of changes. Screenshot every adjustment. Catch app auto-changing issue sooner. More systematic optimization tracking.
5. Consider Asbestos Testing Earlier - Test BEFORE breaking boxing (Sept 2022). Could have avoided £1,500 removal. Or planned for it better. Proactive vs reactive.

What I'd Do The Same

1. Loft First - Absolutely right priority. Foundation for everything. No regrets.
2. Strategic Radiator Oversizing - Enabled 50°C flow temps. Made 826 boiler viable. Screwfix deal made it affordable. Key decision.
3. Right-Sized Boiler - 826 vs 32-36kW recommendations. Modulation matters more than maximum. Validated by results.
4. OEM Controls - Weather compensation essential. Heat curve optimization critical. £94 extra cost worth it.
5. Phased Approach - Accept budget reality and work with it, because incremental progress is better than waiting, with each improvement potentially funding the next one through the savings it generates.

Living With The Results: Daily Reality

Morning Routine

• Check myVAILLANT app (outdoor temp, system status)
• Verify heat curve setting (app keeps changing it)
• Kitchen slightly colder first thing (efficient boiler = no waste heat)
• Prop door open to circulate warm air
• Comfortable throughout rest of house

Heating Control

• TRVs on each radiator (game changer)
• Heat living room without wasting energy on bedrooms
• Set individual room temperatures rather than one-size-fits-all
• No more "all or nothing" heating that wastes energy
• Weather compensation handles flow temp automatically based on outdoor conditions

Comfort Improvements

• No cold spots (landing was always cold before)
• Even heat distribution (convector radiators)
• Rooms warm faster
• Lower flow temps feel gentler (not blasting heat)
• Sound reduction from windows noticeable
• Radiators safe to touch - 28-50°C vs dangerous 75°C traditional systems

Energy Monitoring

• Daily app checks (almost habit now)
• Monthly consumption reviews
• Seasonal pattern understanding
• Adjustment when needed (rare)
• Satisfaction seeing low consumption

Hot Water

• Combi = instant hot water (huge upgrade from old system)
• Wife taking more baths (quality of life)
• Children growing = more DHW needs
• No storage tank = more space
• Consistent temperature (no running out)

Maintenance

• First boiler service included (free)
• Second service due soon
• Heat curve verification regular (app issue)
• No other maintenance needed
• 7-year warranty = peace of mind

The Unexpected

• Kitchen colder (boiler efficient)
• Heat curve app issue (frustrating)
• But: Overall much better
• Comfort + efficiency both improved
• Would do it again

Advice for Someone Starting Today

Ten practical recommendations based on five years of real-world experience.

1. Start With Insulation
   • Loft first (cheapest, highest ROI)
   • Walls if needed (cavity/external)
   • Floor if accessible
   • "Retain heat before adding heat"
   • Foundation for everything else
2. Establish Baseline
   • Year 1 consumption data critical
   • Measure AFTER insulation
   • Track daily/monthly patterns
   • Everything measured against this
   • Don't skip this step
3. Think System, Not Components
   • Radiators + boiler + controls work together
   • Each improvement enables next
   • Synergistic effect > sum of parts
   • Strategic sequencing matters
   • Plan the complete journey
4. Don't Oversized Boiler
   • Modulation matters more than maximum
   • Calculate actual need
   • Account for insulation improvements
   • Challenge installer recommendations
   • Lower minimum output = better efficiency
5. Oversize Radiators
   • Enable 50°C flow temps (vs 70°C)
   • Better condensing efficiency
   • Works with right-sized boiler
   • TRVs essential (room control)
   • Convector fins critical (not flat panels)
6. Choose Controls Carefully
   • OEM controls preserve boiler features
   • Third-party (Nest/Hive) lose modulation/weather comp
   • Understand trade-offs
   • Weather compensation valuable
   • App UX vs efficiency (pick priority)
7. Budget Realistically
   • £13,149 over 4 years (our total)
   • Phased approach acceptable
   • Each improvement funds next
   • Incremental progress > waiting for perfect
   • Accept budget constraints
8. Accept Imperfection
   • Mistakes happen (our electrical redo)
   • Budget forces compromises (phased windows)
   • Timeline slips (loft Phase 2 gap)
   • Technology has bugs (heat curve app)
   • Perfect is enemy of good
9. Monitor & Optimize
   • Track consumption regularly
   • Adjust when needed
   • Learn system behavior
   • Don't set-and-forget
   • Ongoing optimization valuable
10. Non-Financial Matters
    • Comfort improvement huge
    • Reliability valuable
    • Peace of mind real
    • Safety matters (child-safe radiators)
    • Strategic sequencing > spreadsheet ROI
    • Quality of life counts

Conclusion

Five years. £13,149 invested. 45.4% reduction in gas consumption.

From £1,166/year to £636/year. From cold spots and inefficient heating to comfort and optimization. From 1970s technology to modern efficiency.

This Wasn't a Clean Success Story

• Electrical work done twice (should have planned better)
• Window inflation cost £189 (phasing penalty)
• Christmas heating installation stress (poor timing)
• Heat curve app keeps changing settings (ongoing frustration)
• Kitchen colder in mornings (efficiency trade-off)

But It Was Worth It

• £530/year saved at current prices
• Comfort dramatically improved
• No more cold spots (landing transformation)
• Individual room control (TRVs game-changer)
• Sound reduction (windows)
• Modern, reliable system (7-year warranty)
• Strategic foundation for future
• Safe radiators for children (no burn risk)

The Key Insights

1. Strategic Sequencing

Loft → Windows → Radiators → Boiler. Each improvement enabled the next. Foundation before optimization.

2. System Thinking

Not components in isolation. Radiators + boiler + controls work together. Synergistic effect: 45.4% > sum of parts.

3. Right-Sizing Beats Over-Sizing

826 boiler vs 32-36kW recommendations. Modulation matters more than maximum. Oversized radiators enable smaller boiler.

4. Accept Imperfection

Budget constraints force phasing. Mistakes happen (electrical redo). Technology has bugs (app issue). Perfect is enemy of good.

5. Monitor & Optimize

Year 1 baseline critical. Track consumption regularly. Adjust when needed. Ongoing optimization valuable.

Would I do it again?

Absolutely. The comfort improvement alone worth it. The efficiency gains validate the approach. The strategic sequencing proved correct. The safety benefits for our children invaluable.

Sometimes the long game is the smart game.