Guidance On Heating Your Self Build

When it comes to heating our homes, we all ideally want a comfortable space that does not break the bank or destroy the earth to create. In order to achieve this, there are a number of details that need to be sorted out and understood very early on.

INTEGRATING YOUR HEATING SYSTEM EARLY

In a new build scenario, we may in the past have built the house and then thought about the heating system at a later stage, which would usually be radiators bolted under the windows and a boiler hanging on the kitchen wall. That is no longer the case. We need to design the heating system into the fabric of the home and make sure that everything is congruent.

A heat loss calculation will be useful based on the anticipated insulation factor of the fabric of the building so that you know how much heat is required in each room. The south side rooms will potentially be warmer than the north side rooms, and there may also be variation between rooms according to how many outside walls the room has, but it is also important to know what type of heat you are trying to keep in or out of the building.

Heat moves in three ways. Radiance, Convection and Conduction. Radiance is like the sun. If you were standing outside on a cloudy day and the sun peeped out from the cloud, you would immediately feel the heat, even through a jacket, but you might not take the jacket off because the air is cold around you.

Now think of a conservatory or greenhouse scenario. The radiant heat, due to its frequency, can pass through the glass roof and windows. The rays then strike the solid floor and get absorbed by that solid mass. After a while, if you touch the floor, you will feel that it has warmed up.

That touch warmth is conductive heat. It is transferred through physical contact. After a bit more time you will be able to feel some heat when you hold your hand above the floor. This is convection. It is a bit more of gentle heat and is the heat you feel when the air heats up.

Radiant heat, conductive heat and convective heat all have very different frequencies, and as such, each one is better at passing through different materials. The radiant heat could easily pass through the glazing on the wall and roof, but the convection cannot. The room, therefore, heats up rapidly.

UNDERSTANDING HEAT LOSS

When we approach the thermal comfort of a building, we really need to try and understand what type of heat transfer we are trying to mitigate. Not only will we want to keep heat in winter, but we will also want to be able to keep heat out in summer.

Therefore, different types of insulation will need to be used, or even combinations of different types of insulation, depending on the construction methods used in the fabric of the building and the emitter circuits and flow temperatures used in the central heating circuits.

It is also worth understanding that air has a specific heat capacity of just less than a quarter of the specific heat capacity of water and around a third of the specific heat capacity of masonry.

This means that the walls and floor of your property will potentially hold three times more heat than the air and take three times longer to heat up than the air. The more masonry you have, the longer it will take for the building to warm up, but conversely, it will also take three times longer to cool down.

This is where heating controls are vitally important. Your emitter circuit flow temperature will always be warmer than the air temperature, and as such, if you put too much heat into your underfloor heating when it is 0 degrees outside, then you may end up over heating the home tomorrow when the ambient temperature is 7 degrees due to the slow reaction time of the heat in the floor and the higher flow temperature.

Once you have sorted out that part of the heating puzzle, you want to start thinking about what sort of technology will provide the heat to the property. You now need to understand that there is a difference between heat loss and heat load.

They may sound like the same thing, but heat loss is the amount of heat that leaves the building by passing through the fabric of the building through radiance, conduction or convection, as well as the heat lost through ventilation.

The heat load is the amount of heat that the heat source (boiler, heat pump, etc.) needs to put into the building to maintain the desired internal temperature. As I mentioned, this may seem like the same thing, but in modern homes where there is a good level of insulation and draft proofing then all the heat that is generated from other activities such as cooking, showering, running appliances, human occupancy (just by sitting in a chair we generate around 190 Watts of heat) and solar gain contributes to the heat in the home.

Therefore, if the home needs 6kWh of heat to stay warm but we recover 3 kWh from the other activities, then the boiler only needs to add 3kWh.

This is the heat load. The heat load does, however, change according to occupancy and other factors, so the heat source needs to be able to efficiently cover the worst-case scenario as well as be able to ramp down on milder days when there is also perhaps a lower occupancy.

Good design is crucial but in order to get good design we need you to define your requirements and expectations.

David is an authority in sustainable building and energy efficiency, with extensive knowledge in building fabrics, heating systems, heat recovery ventilation, emerging technologies and much more. David often works with architects and house builders and designs and project manages appropriate performance tech and heating systems to achieve the healthiest outcome for every home.

Guidance On Heating Your Self Build - By David Hilton