Historic Churches 2022

BCD SPECIAL REPORT ON HISTORIC CHURCHES 29TH ANNUAL EDITION 7 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, spread- out 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. 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