heating review · next retrofit

Book the loft hatch first

The survey estimates 265 W of heat loss through the hatch, slightly more than through the floor. Sealing it costs £180, takes an afternoon, and can happen next week. The bay window has a larger estimated loss, but secondary glazing costs £1,180 and has a three-week lead time.

The bay window has the largest estimated loss

These estimates use a 20°C difference between inside and outside. They compare the size of each loss, not the savings a finished job will achieve.

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  ariaLabel: "Estimated watts lost by element: bay window 410, loft hatch 265, timber floor 240, front door 155, chimney 120",
  marginBottom: 40,
  marginLeft: 150,
  x: {grid: true, label: "estimated watts lost"},
  y: {label: null},
  marks: [
    Plot.barX(
      [
        {element: "single-glazed bay window", loss: 410},
        {element: "uninsulated loft hatch", loss: 265},
        {element: "suspended timber floor", loss: 240},
        {element: "front door and letterbox", loss: 155},
        {element: "chimney with no cap", loss: 120},
      ],
      {x: "loss", y: "element", fill: "var(--series-1)", sort: {y: "-x"}},
    ),
    Plot.ruleX([0]),
  ],
}

Which measure should be booked first?

The three jobs below have current installer access and quotes. Rank their estimated loss against cost, lead time, and disruption — not as promised savings.

Seal and insulate the loft hatch £180one afternoon

Estimated loss: 265 W. The installer can do it next week.

Add secondary glazing to the bay £1,180three-week lead

Estimated loss: 410 W. The internal panel leaves the sash untouched.

Insulate under the floorboards £2,100room closed for a week

Estimated loss: 240 W. It makes sense only before the planned refinish.

The January draught-proofing may already be helping

Four weeks after the 12 January work sit below five earlier weeks at similar outside temperatures. At 4°C, separate straight-line fits put the post-work readings 43 kWh a week lower. I excluded the shortened boiler-service week. This suggests a reduction, but four post-work observations and no control house cannot estimate its size.

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  ariaLabel: "Weekly gas use against outside temperature: the four weeks after the work sit below the five before at similar temperatures",
  marginBottom: 40,
  grid: true,
  inset: 8,
  x: {label: "outside average, °C"},
  y: {label: "gas, kWh a week"},
  color: {
    legend: true,
    domain: ["before", "after"],
    range: ["var(--series-1)", "var(--series-2)"],
  },
  marks: [
    Plot.dot(
      [
        {outside: 2.1, gas: 604, period: "before"},
        {outside: 3.0, gas: 588, period: "before"},
        {outside: 3.4, gas: 561, period: "before"},
        {outside: 5.0, gas: 512, period: "before"},
        {outside: 6.1, gas: 470, period: "before"},
        {outside: 2.6, gas: 542, period: "after"},
        {outside: 3.8, gas: 498, period: "after"},
        {outside: 5.2, gas: 470, period: "after"},
        {outside: 6.4, gas: 449, period: "after"},
      ],
      {x: "outside", y: "gas", fill: "period", r: 3.5},
    ),
  ],
}