Reaching the Target
How historic places of worship can become net zero carbon
Matt Fulford
Under-pew heaters at St Andrew’s Church, Chedworth which can be switched on for the duration of the service to provide heat where it is most needed
The Church of England has set a target for the whole of the church to be net zero carbon by 2030, with many other faith organisations setting similar ambitions.
This means that within 7½ years most of the nation’s historic places of worship will need to find a way of functioning without burning fossil fuels (gas, oil, LPG or even coal). Is this even possible and, if it is, what needs to be done to achieve net zero carbon (NZC)?
According to Catherine Ross, Open and Sustainable Churches Officer for the Church of England, this landmark decision was passed by the General Synod in February 2020 because of the climate crisis and the fundamental injustice that it impacts hardest the poorest countries and the poorest people.
“Since then”, she explains, “our shoulder has been to the wheel, measuring our emissions, creating plans, revising our rules and our guidance, seeking funding, and – more than anything – engaging people around the country.”
From hundreds of energy audits that have been conducted across church buildings it is clear that it is the fossil fuels used for heating that is by far the major contributor to climate changing greenhouse gases.
In most cases over 90 per cent of the energy and carbon emissions of a church are from the heating. The challenge of delivering net zero carbon is therefore a challenge of moving church heating away from oil and gas and to use electricity instead.
The good news is that we are not starting from scratch as there are already many net zero carbon churches. Back in 2010, St Michaels, Withington became the first in the modern era to convert itself to an NZC church.
As Catherine points out, “Net zero carbon isn’t just a nice theory. Of the 4,000-plus churches completing our Energy Footprint Tool, seven per cent are already net zero carbon.
They have generally got there through making sensible changes to cut energy use, such as LED lighting and fixing broken windows, and they have electric heating which is being powered by a 100 per cent green electricity tariff and/or solar panels.”
So achieving net zero carbon in churches is not only possible – it is already a reality. Most churches that are already achieving NZC are smaller churches that are used once a week, which have direct electric heating and procure their electricity from 100 per cent renewable sources.
Inspired Efficiency was recently commissioned by the CofE to conduct a practical research study to review the energy saving and decarbonisation solutions in its larger, more frequently used buildings.
This study sought to determine if the achievement of NZC was possible in larger churches (as well church schools and theological colleges), and we found it is.
Different solutions and approaches are needed within different buildings. There are a number of issues to consider and technical solutions to work through.
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| The nave of St Andrews Church, Chedworth, Gloucestershire: like most parish churches with high ceilings and large planes of leaded lights, it is difficult to heat efficiently. |
Heating Priorities: Occupant Comfort or Heritage First?
Most are rightly concerned that the historic built fabric needs to be considered within the heating solution.
Generally, the historic fabrics’ prime need in terms of its internal environmental conditions, is one of stability, in both temperature and humidity.
Stability can normally be achieved in one of two ways. One is to provide some level of constant heating to the building 24 hours a day, seven days a week.
The other is the opposite, which is not to have any heating on in the building at all.
Thousands of our churches achieved stability in their internal environment for centuries without any heating and it is only in the past 150 years that we have had the means with which to provide forms of centralised mechanical heating in them.
The problem with constant background heating is that it is costly both in financial and carbon terms.
The problem with no heating is that for at least four months of the year, the building becomes practically unusable as there is no thermal comfort for its occupants.
The challenge is how to find the best compromise between achieving the requirements of the fabric and the requirements of the occupants in a way that is both economically and environmentally friendly.
Sunday Churches
A large number of our historic churches tend to be primarily used (and therefore have a requirement for thermal comfort for its occupants) for just over an hour during a Sunday service.
There may also be some other occasional usage during the week for bell ringing practice, choir rehearsals or a mid-week short morning service but in total the heating demand for the entire week is likely to be less than eight hours and in small, spreadout bursts.
While this type of church is significant in terms of absolute numbers of buildings, their energy and carbon usage tends to be very low indeed.
For this type of church, the general approach is to avoid background heating
1. Operating on a principle of achieving stability of the environment by having no space heating tends to be preferable. The often heard saying ‘I run the heating for one hour every morning to keep the chill off’ should be avoided as it can be highly damaging to both the fabric and the environment, with no benefit whatsoever.
What is interesting in this circumstance is the relative low priority for insulation within the historic fabric. There is no realistic prospect of retaining heat from one heating event to the next as they are often spread out by many days. The building’s heat loss becomes largely irrelevant and calculating the heat loss through modelling can be misleading.
What is important is to provide some level of thermal comfort so that the building can be used, enjoyed and continue to have a strong purpose in the community. To provide this thermal comfort in a net zero carbon way is likely to involve two things.
Firstly, keeping unpleasant draughts to a minimum and secondly, by introducing some form of direct electric heating as close to the occupants as possible.
It is not that the heating is trying to increase the air temperature in the entire space to a level which one would associate with thermal comfort (typically 18 degrees in churches) but that the occupants have a sense of warmth directed at them or flowing past them (before it invariable dissipates).
One of the most successful heating solutions in these churches is to consider the installation of good quality, medium output, under pew heaters (illustrated above).
These under pew heaters provide around 300W to 500W of heat output each. (The older tube style heaters provide around one third of this output.) It is the warm air provided from these that warms the person’s feet and lower body and provides a pleasant sense of thermal comfort while the heat rises past them.
As it is the heat rising past the person that is the primary source of comfort, there is no need to heat the entire air volume of the building.
Furthermore, this heating only needs to be turned on for around 20 minutes prior to occupation to allow the heaters to reach full temperature and to take the chill off the pew seat.
While this heating does require significant amounts of electrical energy when switched on, it does not need to run for very long over a week, with the typical duration being 60 to 90 minutes per ‘event’.
There is good news for Church of England churches. From July 2022 this type of heating installation will be classed as a List B item so it can be installed without the need for a full faculty, so long as it meets the conditions of the new Faculty Jurisdiction Rules coming into force.
Other forms of direct electric heating such as far-infra-red panels, or direct infra-red heating can also be considered in un-pewed areas, but careful consideration needs to be given to the visual impact these have on the space and how close they need to be to provide effective heat.
Care should be taken with the position of direct infra-red units as some types can become very hot. Locations immediately next to historic timbers for high output units are best avoided.
Consideration of draughts should not be forgotten as there is little else more detrimental to your thermal comfort than a cold stream of air running down your neck or up your leg.
Making sure the pointing around windows is well maintained and that the doors fit well into their frames has benefits in terms of the comfort of the space.
Where platforms have been used to raise pews, the voids beneath them can be the source of unpleasant cold rising from the ground below, and they are often ventilated direct to outside beneath.
The introduction of some form of insulation under raised pew platforms can be highly beneficial, such as an inverted form of the insulation normally used above ceilings, with some form of breathable membrane supporting the insulation material.
Other ‘softer’ measures of providing thermal comfort should not be lost in the discussion about heating systems.
Cushions in pews to provide a thermal break between the person and the cold surfaces of the pew seat can be helpful.
Having breathable carpet runners on the floor in front of any seat avoids people having to place their feet on hard cold surfaces. Focusing on providing comfort, as opposed to achieving a certain temperature set point, is key.
Daily Churches
At the other end of the spectrum of usage are those, usually large, and frequently urban, churches that are in very regular use every day.
Typically these have a permanent, paid staff team and run outreach and missional events throughout the week supplemented by lettings to other community groups, and by hosting services such as foodbanks, counselling and others.
Due to the usage that this type of church has, the preferred strategy for achieving thermal stability within the fabric is to provide a constant level of background heating (say around 12 to 14 degrees) and then to raise this up during the day or at the time the building is used.
The insulation of the fabric therefore becomes much more critical to both the effectiveness and the economics of the heating system.
Every opportunity should be taken to reduce the thermal loss and adding in appropriate insulation to roof and floor voids is typically the best place to start.
This needs to be done with expert advice. Any thick, solid walls are likely to be relatively reasonable if well maintained in terms of not letting them become damp from poor roof coverings or failing rainwater goods.
It is the windows and the doors that are then likely to be the biggest thermal weakness and careful consideration should be made to any appropriate treatment of those depending on the space.
Small, plain rectangular windows in the likes of vestry and office space may be suitable for a consideration of high-quality secondary glazing that would be inappropriate on fine large and complex stained-glass windows.
The net zero carbon heating solution within these types of churches is likely to be based on a heat pump. These come in many different forms with their own pros and cons.
Air-source heat-pumps include air-to-air, air-to-water and high temperature air-to-water, while those that extract heat from other sources include ground source and even water source heat pumps.
These are all viable options that can work in different circumstances. A ground source heat pump frequently has many challenges in historical settings given the archaeology in the churchyard, because it involves laying many metres of pipes in the ground.
A water source heat pump requires a large body of water such as a lake, river or canal in very close proximity which obviously limits its applicability.
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| The heat-exchanger of an air-source heat pump on a chancel wall |
Therefore, air source heat pumps (both air-to-water in their low and high temperature forms, and air-to-air) are often the most viable types of heat pump to consider.
Air-to-water systems can be the more obvious choice where there is underfloor heating already installed which remains on all the time, and where the building has a good level of insulation solutions may need ‘topping up’ with another solution such as direct electrical heating on the coldest winter days or for events with higher comfort requirements.
One of the key findings from the CofE Wayfinders programme was the relevance of an air-to-air heat pump solution within churches which are used daily.
Most will be more familiar with this form of air source heat pump when it operates in its cooling mode as an air conditioning unit.
In its heating mode it can send warm air into a space relatively quickly and with higher efficiencies than an air-to-water heat pump which has to transfer its heat into water circulating around a heating system.
It does have the disadvantage of requiring a fan (both inside and out), and while both fan units are now supplied with extremely quiet noise ratings (when installed correctly), there is no escaping the fact that there is a fan.
As most readers will have had a good night’s sleep in hotel rooms with AC units, we know that the fan noise need not be unbearable.
The heat pump market is now producing internal units that move away from the classic lumps of white plastic often seen at high level on a wall in an office meeting room and there are units which can be located on the floor and are hard to distinguish from a fan convector heater.
For those churches that are used often and currently have fan convector units, this solution is an easy substitute and one that other churches that are used daily should consider.
The use of refrigerant gases within these systems needs to be a consideration. These gases have a highly potent ‘global warming potential’ but only if they escape into the atmosphere, so the key is to make sure that they don’t escape.
Having short pipe runs with few joints is helpful in this. The reality is that well installed short lengths of refrigerant pipework in static buildings are at much lower risk of leaking than the AC system in cars.
Adjusting to the 'New Normal'
In summary, the route to decarbonisation can often be found with direct electric heating in little used churches and heat pumps (most likely in the form of air-to-air units) in daily used churches.
The challenges come with churches that have a usage between these two ends of the spectrum, or are little used but have removed all of their pews.
These circumstances certainly require some expert advice on their individual circumstances. We all have to rapidly move to a new normal where gas, oil and LPG are assigned to history.
Where gas mains and oil tanks are replaced for higher levels of incoming electrical capacity and where comfort is as important as flexibility.
We can achieve the NZC target with today’s solutions and in a way that makes our historic buildings more comfortable, more relevant and better able to continue their future on a more stable planet.
1 Any proposal to go from some background heating in a historic building to none must only be implemented with professional advice and supervision giving due regard to the specific individual nature of the building, a review of any special features such as wall paintings and consideration of internal artefacts including fabrics and instruments.
