One of our children has asthma. Will this alleviate her condition?

Yes. MVHR systems have been clinically proven to improve the living conditions of sufferers of asthma and other respiratory conditions. While G4 filters are used to filter air of airborne debris that could potentially harm the fans F7 grade filters can be fitted to filter pollen from the air.

Can an MVHR system be retrofitted into an existing property?

Yes. Retrofitting the system into a single storey house is usually no problem but it more difficult in two storey house unless considerable renovation work is also being undertaken. However it is important to ensure the house is sufficiently air tight to warrant the spend. If not, Demand Controlled ventilation may be the more appropriate system.

Can my MVHR system filter agricultural smells from the air?

Yes. Additional charcoal filters can be fitted in an inline filter box installed between the MVHR unit and the fresh air intake. It is important to ensure the unit is sufficiently sized to cater for the resistance produced by this additional filter.

Will my system cool my house in the summertime?

During the summer months as temperatures rise MVHR units will be in bypass mode. Rather than recovering the heat from the stale air the system just expels it outside. Consequently the incoming fresh air provides a cooling effect in the house. It is important to note however the definition of fresh air in this case is whatever temperature it is outside. If additional cooling is required an additional cooling system is required.

How do I know my MVHR system works?

It’s a commonly asked question. The electrician has done his job if the light comes on. The plumber has done his if the water flows. However how do you know if your ventilation contractor has completed his job correctly? You can’t see air like you can light or water. In a bid to answer this question we suggest turning off the MVHR unit temporarily. Assuming the house is built to a relatively air tight level air quality should deteriorate quickly and air quality will suffer. You will find yourself wanting to turn it back on before too long. This simple experiment should demonstrate the effectiveness of your MVHR system.

What level of air tightness is recommended for MVHR to work efficiently?

MVHR systems are recommended in houses where infiltration rate (air tightness test result) is 5 m3/h m2 or less at 50Pa. The better sealed the house is the greater the requirement for mechanical ventilation. This is why ventilation is so important in low energy houses.

How are the ventilation rates calculated?

Typically, the minimum ventilation rate is calculated by multiplying the total internal floor area by 0.3 l/s/m². The boost rate is calculated by assigning the following vent rates to each wet-room, and then adding them together. (kitchen 13l/s, bathroom 8l/s, utility 8l/s, WC 6l/s). It is important to note that these flow rates are to meet the minimum regulations. In many cases systems should be designed to allow for up to .5 l/s/m2. It may not always be required but when asked the system, should be able to do it comfortably, quietly and efficiently.

Are Semi Rigid/ Radial duct systems as efficient as rigid ducting and is it SAP tested?

The semi-rigid ducting system has been classified as equally efficient in performance as the rigid duct work. See notes on the SAP Appendix Q website:

“A Semi-Rigid duct system is defined as a unique product supplied by a manufacturer or supplier comprising the components required for assembly of that system. Systems listed within the SAP Appendix Q database have demonstrated that their performance, when installed in a variety of configurations, is at least equal in terms of aerodynamic performance to SAP performance data for Rigid duct. It is therefore possible to select Rigid duct performance data when listed Semi-Rigid duct systems are specified for a dwelling. Refer to Specification Requirements for further details.”

Where are MVHR systems installed within the home?

MVHR systems should be installed within the thermal envelope where possible. This should be considered at design stage to ensure adequate provision of space for the MVHR unit and duct system throughout the house.

What other aspects of the ventilation system should be considered when designing a house?

There are many things to consider when designing a house to ensure the heat recovery system can be installed correctly and will perform as efficiently as possible.

  • Location of the MVHR unit.
    • The unit should be installed within the thermal envelope of the house to ensure maximum efficiency.
    • The MVHR unit itself should be installed centrally within the house as this assists in the correct distribution of air.
    • MVHR units should not be installed near bedrooms where possible. If installing in the attic or other space the unit a suitably insulated unit should be chosen.
    • Safe access to the unit should also be ensured to allow for regular maintenance of the system.
  • Access to atmosphere.
    • Every MVHR system must be ducted to atmosphere. One duct to carry the fresh air in to the house and another through which the stale air is exhausted. These ducts can be anywhere between 150mm and 250mm in diameter depending on the volume of air required. Cowls can be wall or roof mounted. Ventilation poles can also be installed where MVHR units are installed in basements. (link to ventilation poles here)
  • Condensate drain.
    • Most MVHR units, except for units that use rotary wheel units, need to have a condensate drain fitted. This should be plumbed into the waste water system within the house. It should not be piped directly to atmosphere such as a down pipe or gutter as it may freeze in cold conditions causing the water to overflow from the MVHR unit.
  • Prevailing winds.
    • It is important that the air intake and exhaust are as sheltered as possible.
  • Distance between supply and exhaust cowls.
    • A minimum of 1.2m is recommended between them. Consideration should also be given to the prevailing wind by keeping the exhaust cowl downwind where possible.
    • The supply cowl should be kept as far away from the chimney as possible, again, with consideration given to prevailing wind direction.
Can I install a stove if I have an MVHR system?

We recommend installing a stove with an external air supply. This means that the air required for combustion comes from outside rather than from the room.

How is an MVHR unit controlled?

At a minimum MVHR units can be controlled with a speed controller but nowadays most come with remote digital controllers. Boost buttons are also an option outside bathrooms however humidity/ VOC and CO2 sensors can be connected to offer a “demand controlled” element to the system.

How much will I save on my heating bills?

The idea that you will save hundreds on your heating bills is somewhat of a myth.  After all most new houses only cost several hundred euro to heat in the first place. Unlike heat pumps or photovoltaic panels your MVHR system will never pay for itself, not ours or others. While a heat recovery system may recover several hundred euro worth of heat this typically only covers the cost of the electricity to run the unit and a 12 month filter change.

Yes, heat recovery is a valuable aspect to any MVHR system but it is important to understand that it is only secondary to the ventilation function which ensures excellent indoor air quality and prevents mould or condensation issues in the home.

Will my MVHR system heat my house?

MVHR systems are designed to re-use the waster energy from your home. In some, ultra low energy houses, MVHR systems which are fitted with an optional post heater can provide sufficient heat however in most houses a primary heat source such as a heat pump is still required.

How much electricity will my MVHR unit use?

As all of our MVHR units use the latest in high efficiency EC fans electrical consumption is minimal. Approx €20-€30 per year will power an MVHR system required to ventilate a standard 3 bed house. Not bad considering it is the lungs of your home.

Can I open my windows?

Yes you can however in winter it will reduce the efficiency of your unit slightly. During the summer it really doesn’t make any difference. Your unit will be in bypass mode anyway thus preventing heat transfer. Some might ask if they can turn the unit off during the summer when they open windows. It is important to note the extract function will also be lost so turning the unit off should be avoided.

Are MVHR units noisey?

No. Sized correctly our MVHR systems will run very quietly. Fan manufacturers say that their fans should not run continuously above 60% approx. We design systems so they won’t have to run at more than 50% on normal mode.

What maintenance is required?

MVHR systems require a filter change every 6 to 12 months, depending on where the houses is located and the surrounding environment. It is also recommended that every two to three years the heat exchanger and the blades of the fans are cleaned to ensure efficient and long term performance of the system. Filters can be ordered online or phone.

Can a cooker hood be connected to an MVHR system?

It is not recommended as grease will still penetrate the filters in the cooker hood and cause damage to MVHR unit. We recommend installing aa conventional hood ducted to atmosphere in conjunction with a Flow Star or Thermobox flue closer. Both products will maintain an air tight seal in the duct when the hood is not in use.

What if I go on holidays?

You should leave the system running 24/7 even when you are away. However you can set it to holiday mode which will reduce the flow rate to just the right amount to keep your house fresh, saving energy in the process.

Why do we need MVHR?

Simply put, heat recovery systems are the lungs of our homes. In the past, our houses were leaky and difficult to heat. Recent changes to building regulations and modern building practices have resulted in us building ultra-low energy houses, some even capable of heating themselves. However, none of them are capable of ventilating themselves which is why mechanical ventilation is such a critical component of the modern-day home.

Benefits of MVHR
  • Ensure excellent indoor air quality
  • Protect against mould & condensation issues within the home
  • Recover up to 98% of heat typically lost with passive systems
  • Clinically proven to help sufferers of asthma and other respiratory problems
  • No trickle vents or bathroom fans required.
  • Allow you to ventilate your home securely without having to open doors or windows.
  • Your home will be quieter and draught free
  • Remove unwanted cooking smells and other odours.
  • Helps prevent build-up of potentially lethal radon gas
  • Are environmentally friendly and are a recommended in Part F of Irish TGD.
Features to look for in MVHR systems

The standard of MVHR system is very high nowadays. Features to look out for include:

  • Greater than 90% efficiency
  • High Efficiency EC Fans
  • Counter Flow Polystyrene Heat Exchangers
  • Automatic Summer Bypass
  • Built in Humidity Detection
  • Frost Protection
  • Digital Controller
  • Extended Warranty
How often do I have to change filters in my heat recovery ventilation system?

Generally it is recommended that you change filters every 6-12 months however this will also vary depending on location of your home and proximity to trees and other foliage.

Where can I get filters for my MVHR system?

You can order filters from us either online at  www.theventilationstore.com or by calling us on 058 20005.  Alternatively you can complete a contact request here.