No central heating needed

The space heating requirement in a Passive House is so low that there is no need for a traditional space heating system. In fact most Passive Houses have no conventional heating and nevertheless stay perfectly warm, even in cold continental winter climates. Solar gain, heat from cooking, lighting and computers and the 60 -100W of heat everybody emitts is normally enough to replenish the tiny thermal losses in a Passive House. A small backup heater is nevertheless necessary for those days in winter when there is hardly any solar gain.

A word of warning though: Please do not attempt to build a house without a heating system without gaining professional advice first. The adhearance to certain u-values does not garantee that the thermal performance of the house is enough to meet passive design criteria. Please contact us if you need to calculate the heating demand of your development.

One way of transferring the small amount of necessary heat is through the mechanical ventilation system. Below, you will find details of typical back-up heating systems used in Passive Houses to provide thermal comfort. Space heating demand in a Passive House is typically met through passive solar gains (40–60%), internal heat gains (20–30%) and the remainder (10–40%) needs to be provided from separate heating systems. The PHPP software will accurately predict the following two measurements for each Passive House design:

• Annual Space Heat Requirement - this measures the amount of energy that is needed to maintain a comfortable indoor temperature, specified in kilowatt hours per square metre of treated floor area per year, or kWh/(m2a).

• Heat Load - this measures the capacity of the space heating system required to maintain comfortable indoor temperatures at any one time, specified in Watts per square metre of treated floor area, or W/m2. For a house with, for example 110m2 treated floor space, if the annual space heat requirement is at the maximum of 15kWh/(m2a), the energy consumption for heating would be 1,650 KWh over an entire year. This would equate to approximately 165litres/year of oil, 165m3/year of mains gas or 330kg/year of wood pellets (depending on the efficiency of the systems).

The maximum heat load, on the other hand, is 1100 W, or just over 1 kW. This amount of output could be provided by a very small stove / heater / boiler compared to what might be typically required in a family home. The most common method of heating a Passive House is by post-heating the fresh air via a heat register after it has already been warmed by the exhaust air in the MVHR. This could either be a water-to-air heat exchanger (which can be fed by all kinds of heat sources, even solar thermal or heat pumps) or an electrical air heater.

a) Water-to-air heat exchanger

This method involves using a heating device placed immediately on the fresh air supply outlet of the MVHR. There is a small radiator inside this device and it is heated by hot water (coming from a boiler, a heat pump, or a thermal store which in turn has different sources of heat). If the house needs additional heat (which is determined by a thermostat), then hot water is circulated through the device, hence the appropriate title of ‘water to air heat exchanger’. Once the house has reached the programmed temperature (usually 20ºC), the hot water stops circulating and the air is no longer heated.

b) Electrical air heater

This again is a small device positioned at the fresh air supply outlet of the MVHR. But this time, it simply containes an electrical heat element which is switched on and off according to the temperature in the house.

Sometimes, you will also find compact units, where the MVHR and a heat pump are combined in one unit. This is usually connected to a thermal store, into which solar thermal panels and/or biomass boilers can feed their heat. The advantage of a heat pump is that there is a lower primary energy requirement than if heating with direct electricity (approx. 1/3 of the consumption). Then the small amount of left-over heat from the exhaust air of the MVHR can also be recovered. See DHW.

The defroster at the air intake shown in the diagram is generally not needed for houses in the UK (even if no ground heat exchanger is used), as the temperature rarely drops below -5ºC.

PR: wait...  I: wait...  L: wait... wait...  C: wait...  SD: wait...

Individual Room Temperature Control

Different rooms may have different temperatures due to solar gains, occupation and internal heat loads. Room based temperature controls for temperature differentiation between rooms may be necessary if individual comfort requirements are set for different rooms. In a centralised ventilation heating system however, the supply air temperature is constant for the whole house and this would be typical for most houses built to the Passivhaus Standard. Therefore, for example, to get a cosy bathroom, underfloor heating or a towel radiator might be added to lift the temperature level slightly over that of the rest of the house.

Below, you will find a table of CO2 emissions connected to the calorific value of different energy sources. This is also important to consider when designing your Passive House: