Eleven sensors, one boiler, a heat meter on the flow and a target of twelve degrees. Ten of the sensors get there. The one in the north aisle sits at eight and a half whatever the boiler does.
I am the fabric officer for a fifteenth century parish church and the heating is mine.
The system, because none of this makes sense without it.
An oil boiler in an outbuilding, a pumped circuit, and eleven cast iron radiators round the walls and under the pews. Not underfloor and not warm air: water in pipes, which is what these buildings mostly have.
In 2018 we put sensors in. Eleven wireless temperature sensors, one by each radiator, logging every ten minutes to a hub in the vestry, because the diocese would not fund a boiler replacement without a year of data.
And a heat meter on the flow, which measures the energy actually leaving the boiler, in kilowatt hours, because oil in the tank and heat in the building are not the same thing.
The target is twelve degrees for a service, which is what you aim for in a church. Not comfortable. Bearable in a coat.
Ten sensors reach twelve.
They get there at different rates, which is normal: the ones by the door lag, the ones in the chancel come up first.
The north aisle sits at eight and a half.
Eight and a half is not a slow corner. It is a corner that does not respond.
If you fire the boiler for two hours, the other ten climb and the north aisle climbs about a degree. If you fire it for six, they all reach target and the north aisle is at eight and a half.
I have run it for eleven hours, once, on a Saturday in January, at a cost of about ninety pounds of oil, with the church empty, to see where it topped out.
Eight point six.
The radiator is hot.
That is the sentence I have repeated to every person who has looked at this.
It is a big cast iron radiator under the north aisle windows and it runs at flow temperature. I have had an infrared thermometer on it: seventy one degrees at the top, sixty three at the bottom, which is a radiator working properly and giving up its heat.
The pipes to it are hot. The valve is open, and it is a lockshield that I have opened fully and left.
So the heat is going in, and the air is not warming.
What has been checked, and the diocese paid for most of it.
A building surveyor in 2019. Report says the north aisle's fabric is in no worse condition than the south, the windows are the same, and the roof is sound.
A thermal survey in 2020, from inside and outside, on a cold night. The exterior of the north aisle wall reads the same as the rest of the church, which is what you would expect if the heat were staying inside, and there is no plume of warmth escaping anywhere.
Air movement. This was my own theory for two years, because a draught through a building takes heat with it and an old church is full of them.
An air tightness contractor came in 2021 with a door fan and a smoke pencil, and found what he called a normally leaky historic building with no exceptional path in the north aisle.
The heat meter is the thing I cannot get round.
It measures the energy that leaves the boiler. Over a heating season it comes to a number, and that number should equal the heat that ends up in the building plus the losses on the pipe run.
I have done that arithmetic with a heating engineer who does churches, twice.
The building needs about nineteen thousand kilowatt hours to do what it does. The meter says twenty six.
Seven thousand kilowatt hours a year going somewhere that is not the air in this church, in a system where the only place it can go is the air in this church.
His written opinion is that the discrepancy is not explicable by pipe losses and that the meter should be recalibrated.
It was recalibrated. It reads true.
The north aisle.
It is the oldest part of the church. The nave was rebuilt in 1487 and the north aisle is what was there before, and there are two blocked arches in that wall that the guidebook says led to a chapel taken down at the Reformation.
The floor is ledger stones, which are the flat grave slabs people were buried under, and there are eleven of them, and the inscriptions on four are worn past reading.
I am aware of what a person in my position is supposed to feel about that and I would like to say plainly that I feel nothing about it at all. It is a floor.
What I have measured, because I have measured everything else, is the floor temperature.
The nave floor sits about a degree under the air. The north aisle floor sits four degrees under the air, all winter, whatever the boiler does, and it does not move when the radiator runs.
What we do now.
The service is at the chancel end, which it always was, and we put the chairs there and the north aisle has nothing in it but the ledger stones and a table with the leaflets on.
I have stopped trying to warm it. The lockshield on that radiator is closed as of the winter before last, which saves us about four hundred pounds of oil a year, and the diocese was pleased with me.
The heat meter still reads about six thousand over.
I have not raised that, and the reason is the one thing in nine years I have not been able to write down in a report.
I closed the valve on the twelfth of November. The radiator in the north aisle has been stone cold every time I have touched it since.
The sensor beside it still reads eight and a half.