Guides & articles
Guides explain the UK standards behind our apps, with the figures cited to the paragraph. Articles are the tangents: why the apps work the way they do, where a rule came from, what we think matters. Filter by kind, topic, or both.
Which way should my TV aerial point?
At the transmitter serving your area, which is often not the nearest one. How the bearing is worked out, why the rods have to match the transmitter's polarisation, what the channel numbers mean for your aerial, and a worked example from Ofcom's transmitter data.
Sizing radiators for a heat pump: the ΔT problem
Radiator catalogues quote output at ΔT50, a boiler running at about 75 °C. A heat pump at 45 to 55 °C gets half or less of that from the same panel. The EN 442 correction, a table of factors, and a worked example showing why the radiator list nearly doubles.
Pay once, own it
Why Plan CD apps are bought outright rather than subscribed to, what that means for updates and longevity, the one exception and why it is still a single payment, and what we give up by working this way.
Why north-facing rooms need bigger radiators
A north-facing room gets no direct sun to offset its heat loss, so the same room needs more radiator than its south-facing twin. What the 15 per cent uplift covers, what it does not, and a worked example.
No Freeview signal? Check these before calling an installer
A ten-minute checklist for a Freeview picture that has gone: is it all channels or some, has the transmitter changed, is the aerial pointed and polarised right, is it the cable, is it the weather, or is it planned engineering work.
What size flue does a log burner need?
Approved Document J Table 2 in plain English: when a 125 mm (5 inch) flue is allowed, when it has to be 150 mm (6 inch), the rules for rectangular flues and open fireplaces, and why the appliance outlet and the manufacturer can override the table.
Where to put a carbon monoxide alarm for a wood burner
Approved Document J requires a CO alarm in the same room as a new solid fuel stove. Here is the alarm standard it asks for, the ceiling and wall positions with their 300 mm and 150 mm rules, and the 1 m to 3 m distance from the appliance, drawn out.
Can a landlord do their own legionella risk assessment?
For most rented homes, yes. HSE says most landlords can assess the risk themselves without professional training. Here is what to look at, what to write down, what a simple system needs, and when to get help.
How many BTUs does a room need?
How radiator sizing works: the heat a room loses through its walls, windows, floor and ceiling, plus the air changes, worked out for three real rooms, with the conversion between BTU/hr, watts and kW.
How a room heat-loss calculation works
What a U-value is and why it is in watts per square metre per degree, where the 0.33 in the ventilation term comes from, what the temperature multiplier stands for, how to read the heat loss breakdown, and where the trade's quick method stops and BS EN 12831 starts.
Getting Freeview in a caravan or motorhome
Every pitch is a new transmitter. How to rank the sites from where you are parked, why holiday areas are relay country with only three multiplexes, when to switch the aerial from horizontal to vertical, and why you retune at every site.
How to find your Freeview transmitter
Three ways to identify the transmitter your aerial should use: rank the sites from your postcode, read the UHF channel numbers off your TV's tuning menu, or look at the neighbours' aerials. With a table of the UK's main stations and their channels from Ofcom's data.
BTU to watts and kW: the conversion and why both exist
One watt is 3.412 BTU per hour. A ready-reckoner both ways, the arithmetic behind the number, why radiators are still sold in BTU while boilers are sold in kW, and the two mix-ups that cause wrong orders.
TV aerial horizontal or vertical? Polarisation and groups explained
Why the rods on a TV aerial point sideways in some streets and up and down in others, what an aerial group letter means, and why an aerial from before the 700 MHz clearance may be built for channels that no longer exist, with the facts from Ofcom's transmitter data.
Wood burner hearth rules explained
What size and thickness of hearth a wood burning stove needs in England: the 840 mm square, the 125 mm constructional hearth, the 12 mm board exception and the clear surface around the stove, drawn to scale.
Sentinel outlets explained
What a sentinel outlet is, how to pick the right taps in a house or a block, why a circulating system's hot sentinels are different, and what the rotation of other outlets is for.
Do I need a legionella certificate?
No. Health and safety law does not require a landlord to obtain or produce a legionella test certificate. Here is what the law does ask for, why water sampling is rarely needed, and what to say to a company selling you one.
Landlord legionella duties: what the checks actually mean
What a landlord is actually required to do about legionella: assess the risk, control it, keep records. What monthly monitoring involves when it applies, and why most simple domestic systems need far less than that.
How we make sure the numbers are right
Our apps produce figures people build from. Here is the discipline behind them: one archived source document, every constant carrying its paragraph reference, hand-derived test cases, and a "not covered" verdict where the answer is not known.
What temperature should hot water be?
The L8 and HSG274 temperature thresholds in plain English: 60 °C leaving the cylinder, 50 °C at the tap within one minute, below 20 °C on the cold within two minutes, and what counts as a pass at the boundary.
Can I fit a wood burner myself?
You can do the work yourself in your own home, but installing a stove is notifiable building work. Here is the building control route, what Approved Document J will be checked against, and why most people use a registered installer instead.
Why our apps don't track you
Plan CD apps have no accounts, no analytics, no ads and no backend. Here is what our privacy policy actually says, why we work this way, and what it costs us to keep it that way.
Do I need an air vent for my log burner?
Whether a wood burning stove needs a permanent air vent in England, and how big it has to be: the Approved Document J Table 1 rule explained with worked examples for 5 kW, 8 kW and 12 kW stoves.
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