David in Kingston

David in Kingston wrote:

This comes up in search often enough to be worth a thread, and it is one where the honest answer is that this site does not have the whole of it yet. What is on the site: the unit database lists the published noise figure for each unit, and there is a piece on what a noise figure actually tells you, which is less than ...

One thing worth separating out, because people tend to run the two together: whether a unit was allowed to be fitted and whether it is too loud now are different questions, answered by different parts of the council, and winning one tells you nothing about the other.

If you are living with one, the useful thing to post is what your council actually did when you contacted them: who you spoke to, what they measured, and how long it took. That is the part no specification sheet covers.

One thing worth adding, because it is what catches people out after the planning question is settled: permitted development is not the same as your freeholder or your management company saying yes. If you are in a flat, or on an estate with a covenant on the deeds, that consent is a separate conversation and it is the one that more often stops a job that was otherwise fine.

If anybody has been through this with their own council, what they actually asked you for would be worth posting here. The rules are national. How they get applied is not.

This is the question people most often arrive here searching for, so it seems the right place to start the forum.

The short answer for a house in England is that it can be permitted development, and the trap is the one almost nobody mentions: the rules only allow a unit that is not used solely for cooling. A reversible unit, one that heats as well as cools, can be permitted development. A cooling-only air conditioner cannot, at any size, in any position.

The rest of the conditions are about where it goes and how big it is, and the planning checker walks through them one at a time and tells you which condition you fall foul of rather than just saying no.

Two things it deliberately does not cover: it is England only, and it assumes a house rather than a flat. Wales, Scotland and Northern Ireland have their own regimes and are not the same.

If you have been quoted for a cooling-only unit and told it needs no permission, that is worth going back to the installer about.

Another one that comes in through search, and the answer is different from the house answer in two ways.

The permitted development rights that cover an air source unit on a house do not extend to a flat in the same way, so the planning half is more likely to need an application rather than less. That is worth checking with your own council before anybody quotes you.

The other half is nothing to do with planning. A leaseholder usually needs the freeholder's consent to fix anything to the structure or to the outside wall, and an external unit is both. That consent is a separate question from planning permission, it is decided by your lease rather than by the council, and it is the one that most often stops a job that was otherwise fine.

If anybody here has been through it on a leasehold flat, what the freeholder actually asked for would be useful to know.

This comes up in search often enough to be worth a thread, and it is one where the honest answer is that this site does not have the whole of it yet.

What is on the site: the unit database lists the published noise figure for each unit, and there is a piece on what a noise figure actually tells you, which is less than most people assume. A figure measured at one metre in a test chamber is not what you hear through a bedroom window at two in the morning.

What is not on the site, and what I would not want to state without checking properly: the enforcement route. Statutory nuisance sits with the local council's environmental health team, and permitted development for these units carries its own noise condition, but the detail of how those two interact is not something I have written up yet.

If you are living with one, what your council actually did is worth posting. That is the sort of thing no specification sheet will tell anybody.

A conservation area does not make cooling impossible, it makes the outside of the building the problem.

The planning checker has the conservation area conditions in it, and the practical upshot is usually about where a unit may go rather than whether you may have one at all: the front elevation and anything visible from the road are where the restrictions bite hardest.

Worth saying out loud, because it gets forgotten: the things that need no permission at all are often the ones that work best. External shutters, shading, and stopping the sun reaching the glass in the first place do more for a south facing room than a machine fighting the heat after it has arrived. There is a piece on the site about exactly that.

If you have had a conservation officer say yes or no to something, saying which and why would help the next person more than any general advice.

Straight out of the search data, and the answer is a number rather than a word, which is why there is a calculator for it.

The running cost calculator asks for the unit's power, how long you run it and what you pay per unit of electricity, and gives you a cost per hour, per night and per summer in pounds. It defaults to the current price cap but you can type your own rate over it, which is worth doing: the cap is an average and almost nobody pays exactly it.

The thing that surprises people is not the hourly cost, it is the hours. A unit running eight hours a night through a hot fortnight is a very different bill from the same unit run for an hour before bed.

There is also a diagram on the site showing why a single hose portable unit works harder than a double hose one for the same cooling, which is the part of the answer no price comparison covers.

What does your meter say, against what the calculator says? That gap is the interesting bit.

Worth its own thread, because the calculator is only as good as what goes into it.

The usual suspects, in the order they catch people out:

• The rate. The calculator defaults to the price cap, and if you are on a fixed tariff or a time of use tariff, your real unit rate is not that.
• The standing charge. It is on the bill whatever you run, so a bill that went up by more than the calculator said may not have gone up because of the unit at all.
• The hours. Almost everybody underestimates these. A thermostat cycling through the night is not the same as the hours you think you ran it.
• The unit's rated power against what it actually draws. A machine working harder in a hot room draws more than its label suggests.

If you post your unit, your rate, and roughly how long you ran it, somebody can sanity check the arithmetic with you. If the gap is still there after that, it is worth knowing about.

This is the question I have been asked most in person, and I want to be careful about answering it in general terms, because the honest answer is that it depends on the room rather than on the machine.

The physics of it: a room loses the cooling you put into it at a rate set by how well it is insulated, how much glass it has and how hot it is outside. A well sealed room holds it for hours. A loft bedroom under a warm roof does not.

So the two cases are genuinely different, and the way to settle it for your own house is to try both on two similar nights and read the meter rather than trust anybody's rule of thumb.

The running cost calculator will tell you what each pattern costs once you know the hours. What it cannot tell you is how fast your particular room warms back up.

If anybody has actually measured this in their own house, that is worth more than the theory.

The single most common shape of question this site gets, and the reason the room cooling calculator exists.

Start with the heat rather than the machine. The calculator asks about the room's size, its glazing, which way it faces and what is above it, and tells you where the heat is coming from before it tells you what size of unit would remove it. In a loft the answer is very often the roof rather than the windows, and no amount of machine fixes a roof.

In rough order of what tends to help most, and what the site has written up:

• Stopping the sun reaching the glass at all, from outside. External shutters and shading beat anything on the inside of the window.
• Insulation above you, which is a winter job that pays in summer too.
• Ventilation at the right time of night, which is later than most people think.
• Then, if the number still says so, a machine sized to the heat gain rather than to the room.

Post your room and what the calculator said, and let us see whether the number matches what the night feels like.

Outside, every time, and the reason is simple enough to be worth stating plainly: a blind on the inside of the glass stops the sunlight after it has already become heat in your room. A shutter outside stops it before it arrives.

There is a piece about external shutters and shading which goes through the detail, including the part people do not expect, which is that the same shutters help in winter by cutting heat loss through the glass at night.

What the site does not have, and will not invent, is a percentage. The figures quoted around the internet for how much a shutter cuts solar gain vary enormously depending on what was measured and where, and putting one here would be pretending to a precision this site has not got.

If you have fitted either, what changed in the room and roughly what it cost is exactly the kind of thing this forum is for.

Yes, and this is the thing the site is most insistent about: insulation is the same conversation in both directions.

Everything sold as a winter measure is also a summer measure, because it slows heat moving through the fabric of the house whichever way it is trying to go. A loft with a warm roof over it in August is losing that heat downwards into the bedroom, and insulation between you and it is the thing that stops that.

The one thing to be careful about is ventilation. Insulating without thinking about how the roof space breathes is how people end up with a condensation problem in winter that they did not have before, and that is a job worth getting right rather than fast.

Nothing on the site quotes a payback figure for this, deliberately, because it depends on what is there now and what you pay for heat. If anybody has done it and watched what the bedroom did the following summer, that is the number I would want.

A fair challenge, and the answer is on the town pages but is easy to miss, so it is worth a thread.

The series behind those pages is reanalysis data: every reading is the average across a grid cell of about eleven kilometres, not a thermometer in your town. Averaging over an area that size smooths the peaks, so a record here reads a few degrees below the hottest station in the same town on the same day.

That is why those sections are headed "warmest days in this series" rather than "on record". They are not claiming to be the record. They are claiming to be the warmest day in a consistent series that goes back to 1950 and is measured the same way every year, which is the thing that makes the trend meaningful.

If you want the actual station record for your town, the Met Office is the place for it. What this site is for is the shape of the change rather than the single hottest afternoon.

Both, usually, and the town pages exist to separate the two.

Every town page is built from the site's own stored daily series back to 1950, and shows the count of hot days by decade and the trend through them rather than a single number. The stripes on the homepage are the same series for the country: one band per year, coloured by how far that year sat from the 1951 to 1980 average.

Three things about those stripes are honesty decisions rather than design ones. A year only counts when every town covers it in full. The baseline is fixed rather than chosen to suit the picture. And the colour scale is symmetric, so a warm year and a cold year of the same size get the same strength of colour.

Find your nearest town from the postcode box on the heat data page. If the trend where you are looks different from what you expected, say so here: the towns are twenty two places, not a map, and there will be parts of the country the series does not describe well.