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ASHP guide

Air source heat pump calculator: inputs before output

Calculator outputs are only as good as the evidence behind them. Survey quality decides whether the numbers hold up on site.

MCS says compliant heat-load work for heat pumps is room by room. That is why missing room data, weak U-values, or vague emitter notes can make a neat-looking output unusable. · 3 min read

Guide

Inputs that make ASHP outputs usable

What strong looks like

Capture standards

  • Room-by-room dimensions and exposure captured with supporting context
  • Emitter condition and layout documented before sizing decisions
  • Plant location, access routes, and constraints photographed clearly
  • Assumptions recorded so design teams know what is confirmed vs pending
Where time is lost

Where teams lose time

  • Missing evidence around emitters and routing
  • Assumptions buried in ad-hoc notes
  • No consistent move from survey to design
Why it helps

Why teams use Vertex

  • Clearer reports for office and design
  • Faster quoting with less chasing
  • Install teams start with clearer site context
  • Portal visibility across teams and roles
Related guides
What is an air source heat pump? ASHP survey reports ASHP efficiency guide ASHP survey reports Heat loss calculations
Official reference points

What the MCS heat-load guidance expects the inputs to cover

Room by room

MCS says room-by-room heat-load calculations are crucial for sizing low-carbon heating properly. A whole-house shortcut is not the same standard.

Core variables

The MCS documentation points back to building fabric, room dimensions, air-change rates, target internal temperatures, and winter design temperatures as key inputs.

Practical implication

If any of those inputs are guessed badly, the calculator still gives a number. It is just a weaker number. That is why survey quality matters more than the interface.

Sources checked on 17 April 2026: MCS Heat Load Calculator, MCS heat-loss guidance, and MCS room schema. The third card is an inference from those sources plus normal survey practice.

Practical use

How to use this page on a live job

Use this guide as a decision check, not as a generic reading page. The useful question is whether the evidence behind air source heat pump calculator: inputs before output is strong enough for an installer, designer, or homeowner to move to the next step without another round of avoidable questions.

Before booking

Confirm what evidence is missing

For heat pump evidence, the weak point is usually not the headline requirement. It is the missing photo, document, measurement, or site note that stops the next person from trusting the job record.

During survey

Capture the detail once, then label it properly

A survey report should show what was seen, what was measured, what could not be accessed, and what still needs a design or installer decision. That keeps assumptions visible instead of hiding them inside a photo set.

After delivery

Use the report to reduce internal handover friction

The office, design, and install teams should be able to open the same report and understand the evidence path. If the page helps you spot what to ask for before survey day, it has done its job.

For a live project, pair this guidance with the sample report, deliverables, and guide price builder so the job is reviewed against the same standard Vertex uses for survey delivery.