Convection vs Conduction

In is quite common to encounter both convection and conduction heating methods in the same house. Floor heating on the main floor and radiators in the bedrooms for instance. In some cases you can find both types of heating in the same room, convection radiators as the main source of heat and floor heating as an extra. Calibrating radiators and floor heating to work together can sometimes be a challenge. It is important to understand the differences between the two types of heating, especially with a single room thermostat.

Convection Heating - Wall Radiators

There is a long standing misconception that radiators heat a room by radiating heat outwardly.  This is logical as the air closest to the radiator feels the warmest. However, the actual method of heating a room with a radiator is through convection.  Cool air accumulates at the lowest point in a room because it is denser than warm air and the molecules take up less space. The cold air is drawn up through the bottom of the radiator and comes in contact with the heated core.  As the air begins to warm it expands and become less dense. Lighter air rises and the heated air moves upward and along the ceiling of the room in a convection current. As the air moves away from the radiator on the current it begins to shrink as it cools, density increases and the cool air descends back to the floor ready to repeat the heating cycle.  The constant circulation of air moves heat around the room. In addition, the circulating heated air accumulates airborne particles of dust and allergens on the journey and redistributes them around the room as well.  

In cold months radiators require a water temperature between 65-80C. The convection current created can result in a very warm room but a cold tiled floor. Occupants in a bedroom may need to sleep next to the radiator for warmth, but also need a window left open to help ventilate the over-heated space.

Radiator thermostatic control knobs and modern smart thermostats make controlling radiator heat systems easier.  To get the most efficiency out of radiators the air current must circulate freely. This can have restrictive implications for how furniture is placed in a room. A radiator installed under a window with a large overhanging sill or behind a large piece of furniture will greatly reduce its efficiency and ability to move heat throughout the space. Radiators are big dust collectors that also require periodic maintenance to remove air that can accumulate in the system over time causing them to make noise.

Conduction Heating - Floor Heating

In contrast, hydronic heating systems produces radiant heat through conduction. The system pumps water from a heating source (boiler/heat pump) through thermally conductive tubing located in the screed layer of a floor. The heat is transferred to the surrounding screed material (concrete, sand/cement, anhydrite) through conduction. This layer of the floor is insulated so the heat that accumulates does not move downward. Screed is a good thermal conductor and the heat is transferred to the entire floor, radiating warmth upward and warming the floor and everything in the room.  Floor heating essentially turns the entire floor into one gigantic radiator.  This method of heating a space eliminates cold spots and draughts, reduces the circulation of dust and allergens, and allows furniture to be configured without restriction.    

Modern windows and proper home insulation are important factors in retaining heat efficiently and maximising comfort. Likewise, floor coverings are also an important part of floor heating efficiency. Concrete, stone and tile are good thermal conductors and retain heat very well. Wood flooring is less conductive and some types of wood can react to the fluctuation in temperature. When certain rules are followed a wood floor can be installed with floor heating.  Wall to wall carpet has the lowest conductive properties and is not a suitable covering with floor heating.  

The lower water temperature used with hydronic floor heating systems is where the efficiency shines through.  The boiler can be set around 45C, which is enough to create a very comfortable interior and will save on annual utility bills and maintenance. The development of modern smart thermostats have resulted in improved functionality in floor heating temperature control that can be uniquely adjusted for personal lifestyle and needs. However, it is important to note that Smart thermostats require programming to function. There are many manufacturers of smart thermostats and they can all operate differently. The common denominator is that they “learn” how to efficiently regulate a system using algorithms. Smart thermostats require the end user to understand their particular models programming functionality so they can set the system to regulate heat efficiently.