Conservatory Heat Loss - it can be as massif as the gains

You can only be considering heat loss from a conservatory if the thing is to be heated in the first place. Most conservatories are meant to be unheated for compliance under building regulations for the exempt status which most conservatories enjoy.

If one was to do a SAP heat loss calculation for a conservatory as often needed for a new dwelling, you would find that the heat loss is very high even with some of the latest glass and glazing technologies most of which will never meet the thermal performance of a well insulated wall.

However, the SAP heat loss calculations do allow for other energy inputs such as solar gains and from appliances and human bodies for example so it can often a be a bit of ‘smoke and mirror’ techniques when the SAP calculations reveal a theoretical low heat loss and the same can apply to a conservatory.

A very sunny day in mid December can provide high solar heat gains in side the conservatory that would not require any additional energy input so one could argue that the heat loss for the conservatory is very low. However during the evening and night all that embedded heat now contained within the house & conservatory masonry walls and concrete floors is now being released to heat this inside of the conservatory that may provide a very pleasant environment but the heat loss through the glazing and glass will be very high resulting in very rapid cooling of these embedded heat stores.

Most conservatories are also not very tightly sealed with regard to air leakage due to their framed designs and unsealed abutments causing any pre-warmed inside air to leak to the external air very easily. This is another reason why the heat loss from a conservatory can be very high.