Severe High Temperature Tax: The Hidden Cost of UK Heatwaves

Can you claim tax relief? Sometimes. Replacing a freestanding cooling item already provided for tenants may qualify, subject to HMRC’s replacement rules. A fixed air conditioning unit in an ordinary buy-to-let is much harder to claim through capital allowances, although some replacement costs may be treated as repairs depending on the facts. The real question is what you bought, why you bought it, and whether it repairs, replaces or improves the property.

The First Question HMRC Asks: Repair or Improvement? 

For landlords, the tax answer usually starts with one question: did the work repair what was already there, or improve the property? 

A repair puts something back into working order. It can usually be deducted from rental profits. An improvement makes the property better than it was before, so it is normally capital and cannot be claimed as a normal rental expense. HMRC accepts that modern replacements are not automatically improvements. If the new item does broadly the same job as the old one, the cost may still be a repair. 

This matters for cooling costs. Installing fixed air conditioning for the first time is likely to be an improvement. Replacing a broken fixed unit with a similar one is more likely to be a repair. The starting point decides the tax treatment: are you restoring what existed, or adding something new?

Capital Allowances on Cooling Systems: The Residential Trap 

This is where landlords often get caught. 

Air conditioning and air-cooling systems can count as plant and machinery because HMRC treats powered air-cooling systems as integral features. In a commercial property, that can open the door to capital allowances. 

But ordinary residential lets are different. If the cooling system is provided for use inside a dwelling-house, plant and machinery allowances are generally blocked. So a fixed air conditioning unit in a buy-to-let bedroom may look like the right type of asset, but the location can stop the claim. 

There are exceptions. Cooling systems in commercial property can qualify. Systems serving the common parts of a block of flats may also qualify, although costs must be split where the system serves both flats and shared areas. HMOs need extra care because HMRC treats shared HMO areas as part of the dwelling-house, so the block-of-flats logic does not automatically apply. 

Reliefs such as the Annual Investment Allowance or full expensing only help once the asset qualifies for capital allowances in the first place. For a bedroom AC unit in a standard buy-to-let, you usually never get that far. 

Worked Examples 

Here are three common summer situations and how the tax treatment can change. 

Three cooling costs. Three different tax answers. The result depends on what was bought, where it was installed, and whether it replaced something that already existed.

Energy Efficiency, Ventilation & Keeping Homes Cooler 

Cooling a rental home is not always about installing air conditioning. Better ventilation, upgraded insulation, reflective materials or improved window treatments can all help reduce overheating. 

For tax, the important point is whether the work stands alone or forms part of a bigger upgrade. If the job includes both allowable repair work and capital improvement work, the cost should be split fairly. An itemised invoice makes that split easier to justify if HMRC asks questions later. 

Checklist: Before You Claim Cooling Costs 

Before adding cooling costs to your tax return, check these points: 

Conclusion 

There is no official “heatwave tax” in the UK. For landlords, the real issue is how ordinary tax rules treat cooling costs: a replacement moveable item may qualify for Replacement of Domestic Items Relief, while a fixed unit inside an ordinary residential let will usually be blocked from capital allowances. 

Good records protect the claim. Keep invoices, photos and notes showing what was bought, where it was used and why you treated it that way. If the cost is significant, get the tax position checked before filing the return so you know what is claimable.