The capital cost of a Mechanical Ventilation Heat Recovery System (MVHR) varies in proportion to the floor area of the dwelling both in material and installation costs. Besides the obvious effect of the size of the dwelling and the number of rooms, various other factors affect the installation cost, is it an existing or new home? A bungalow or a house? Does the construction allow for easy concealment of the ducts? All factors that affect both the material and installation costs.
As examples, the basic costs of materials for an installation in a two bedroom flat will be as low as Â£1100 with the installation being carried out by two operatives in a single day. For a new four or five bedroom house the material cost would be in the region of Â£1900 to Â£2300, with installation taking the equivalent of four to six labour days during the construction of the dwelling.
Whilst one cannot quantify the householder benefits of a correctly controlled, fresh, pollutant free home environment we can cost the benefits associated with the energy savings of heat recovery ventilation.
The following calculation shows a comparison of the air infiltration heating costs associated with two equal houses one with conventional construction and fan ventilation and one that is tightly sealed with MVHR installed.
Floor area 300m2 â€“ Ventilation by extract fans and trickle vents - 2 air changes per hour â€“ gas heating
Heat Loss due to infiltration at 2 ach 14,164 kWh per year @ £0.0359 per kWh = £508.49
Bathroom and kitchen fan operating cost @ 1 hour per day 0.05 kW = £2.08 per year
Total ventilation energy cost House A £510.57
Floor area 300m2 â€“ Ventilation by MVHR with 71% heat recovery - air change rate 320 m3/h assuming no infiltration (Building Regulation F) â€“ gas heating
Heat Loss due to ventilation at 320 m3/h 7,677 kWh less 71% @£0.0359 per kWh = £79.92
MVHR operating cost @ 24 hour per day 693 kWh = £78.52 per year
Two fans operating in winter, extract fan only in summer. Total ventilation energy cost House B £158.44
By tightly sealing the dwelling and using a whole house balanced ventilation system with heat recovery a total energy cost saving of £352.13 can be achieved each year.
The greater part of the energy saving comes from building a tightly sealed dwelling and controlling the ventilation rate. Additional cost savings may be shown using higher efficiency heat exchangers, for example a heat exchanger having 80% efficiency would increase the saving by a further £24.80 and one of 90% would show a further increase to £52.36.
One should bear in mind that more efficient heat exchangers may increase system resistance meaning that the saving could be offset by a higher specific fan power rating with increased electrical consumption; both aspects should be considered when selecting a system. Regavent MVHR central air units have been independently tested by the Building Research Establishment achieving the following results.