MVHR ventilation is a complex system that moves air, collects water, uses electricity, and reaches every corner of the property. You’ll probably need holes in places you hadn’t planned, including structural members. The insulation line may need altering to change cold voids into warm spaces suitable for ducting. A hot plant room is not the ideal place for air handling equipment if you want to minimise overheating risks, and the MVHR may need to link to other technologies including heat pumps or boilers, AC, or Building Management Systems. There’s more to it than meets the eye.
To ensure things run smoothly we recommend the principal contractor, project manager, and/or site manager review the notes below. Besides coordination the principal contractor is also responsible for providing safe access where needed, for instance between floors if no stairs are installed, or a safe working platform if working at height is required, along with power, water, lighting, welfare, parking, and site security.
Our Projects team will endeavour to provide the right nudge at the right time so you know how to prepare for the MVHR first fix, plant install, second fix, and commissioning visits. Meanwhile, here are some specifics for the rest of the build team..
If we have specified MVHR compatible roof terminals they will be supplied by Solarcrest for installation by your roofing contractor. This is to keep any leak guarantee intact with a single provider. Our MVHR design will show you the precise location, although we understand they may need very minor adjustment to integrate with slates or tiles. Please ensure our designer is aware of the style and colour of slates/tiles planned so we can better match the terminals.
Our install fee excludes the cost of core drilling through solid masonry walls, as this work is often completed by the builder or a specialist contractor depending on the number and size of holes required. In some cases they may need to create a wooden former prior to building a brick or block wall, or pouring the concrete for an ICF construction. Our design will clearly identify the location, diameter, and quantity of holes required.
If our installer can handle the core drilling we’ll provide a competitive price following our pre-install survey.
The Solarcrest commissioning engineer is responsible for everything inside the grey connection box attached to the MVHR unit, as well as the wall mounted remote controller. Everything else, namely the boost switches, cabling, and power, are the responsibility of the site electrician. The following tasks should be completed at their first fix.
Power
Your electrician must install a switched fused outlet above or ideally beside the intended location for the MVHR unit. This must be wired back to its own single circuit fuse in the consumer unit, and protected by common RCD to the machine can be isolated if needed. You can either run a conduit from the outlet to the machine behind the plasterboard, or you can surface mount the conduit later.
Some MVHR units include a built-in Electronic Post Heater for advanced frost protection. If an EPH is installed the unit will draw additional load. Please check the install notes for the unit model and fuse rating. If in doubt, it may be prudent to run cable that will support an EPH regardless, as the occupier may decide to retrofit one later. In a property below 200m2 (i.e. DV50 – DV110) a 1.5mm cable should be sufficient. In larger properties (DV145-DV245) make it 2.5mm.
| UNIT | Max Load WITHOUT Heater | Max Load WITH Heater |
| DV50 | 2A | 6A |
| DV51 | 2A | 6A |
| DV80 | 2A | 6A |
| DV96 | 2A | 6A |
| DV110 | 2A | 10A |
| DV145 | 3A | 12A |
| DV245 | 3A | 15A |
NB: Certified Passive Houses ALWAYS include an electronic post heater.
The fuse should NOT be fitted to the outlet for safety reasons. Our technician will make the final connection from the power lead to the MVHR connection box at the commissioning visit.
Boost Switches
Part-F regulations require a manual boost switch to be installed inside or outside any room with a source of odour, typically all WC’s and potentially the kitchen if requested by the client.
NB: MVHR extraction from the kitchen is required IN ADDITION TO the hob extractor. MVHR does not replace the hob extractor, which should be a recirculating extractor, NOT one vented directly to outdoors.
By default, Solarcrest supply one or more (non-latching) white momentary boost switches that send a 24V signal back to the machine when pressed. No earth connection is required. Your electrician must therefore install standard 100mm pattress boxes in your preferred switch location/s, and then run two core cable from each pattress back to the MVHR unit. Standard 0.75mm to 1.5mm lighting cable will suffice.
NB, If you prefer colour coded switches to match other furniture your electrician will need to source non-latching (sprung-loaded) switches from the same manufacturer.
Each boost switch must have an independent wire running back to the MVHR unit. Boost switches cannot be linked in parallel or in series, or be connected to any other wiring (eg, the bathroom light switch). The boost switch wiring must be installed in conduit, clearly labelled at both ends, and then connected together and terminated in a junction box by the MVHR unit.
Our technician will connect the cables to the boost switches, and to the MVHR unit at the commissioning visit. Please leave at least 200mm of surplus cable at both ends.
NB, we recommend Surewire Prewired lighting spur junction boxes: Click here for details
Wired Remote Controller
Our recommended system, the Airflow Adroit, is supplied with a wall mounted touch screen LCD programmable controller. The controller is wall mounted in a convenient (occasional) location no more than 25m from the machine, although most are installed next to the machine itself as it is used infrequently. Adroit’s are Internet connected for servicing purposes, so are normally controlled by smartphone.
The controller cable must be installed by the electrician at first fix, inside conduit to protect it from damage. No pattress is required. The required cable, a screened 4-core 0.5mm (2 x twisted pair), should be run from the desired controller location back to the MVHR. Our technician will make the final connections at both ends of the cable during the final commissioning visit.
NB: The controller allows you to access all functions of the MVHR at the machine, without needing to go online. Here are some examples of the control cable required:
Room sensors (if specified)
The Adroit MVHR units include six environment sensors that will adjust the ventilation rate automatically if elevated temperature, humidity, or CO2 levels are detected. Additional room-mounted sensors are available if required, for example a humidistat for a main bathroom, or CO2 sensor for the kids bedroom. If optional sensors are specified, your electrician must install a 100mm pattress box in the required location, then run a low voltage cable back to the MVHR from each sensor. Use the same cable as the wall mounted controller (see above).
A domestic MVHR unit extracts the moisture generated by the occupants inside the property, which can be as much as 14 litres/day for a family of four. Most is expelled with the exhaust air, but some condenses inside the unit where it drains away through the bottom of the machine. Your plumber must therefore run a 21.5mm solvent weld condensate pipe from the centre of the proposed MVHR location (every location if multiple units) to the nearest foul waste. This needs a minimum 5-degree fall away from the machine. Our technician will later fit a none-return valve to this prior to making the final connection to the machine.
NB, the water that collects inside machine is contaminated with CO2, VOC’s and other pollutants, meaning it SHOULD NOT drain into the rainwater goods.
The majority of the MVHR units we install are ‘Internet ready’. This is to permit remote control by the user, remote support by our technicians, and firmware updates by the manufacturer. The AV contractor responsible for Internet provision, networking and/or building management software therefore needs to install an ethernet data point within 1m of the MVHR unit. This connects back to the router via a CAT5 or CAT6 cable. Our technician will make the final connection to the MVHR unit.
NB, If the Internet is live at the time of commissioning, our technician will set up the connection. They may require the assistance of your AV contractor, particularly if you have firewalls or other security measures. If the connection is not available, it can still be set up remotely, but you may need the AV contractor on site at the time.
Except for hall, stairs, and landings, every room will have an air supply OR air an extract. Occasionally both. To allow the passage of air from room to room the internal doors must have an 8-10mm undercut between the bottom of the door and the finished floor surface, depending on the width of the door. Please ensure your carpenter creates this undercut before the internal doors are hung.
NB, if the final carpet, tiles, or other floor covering is not yet installed, you may need to leave a 20mm gap or more, depending on the finished level. The regulatory minimum free space requirement is 7600mm2 free space between bottom of door and top of finished floor surface, meaning a 760 internal door needs a 10mm gap..
After our 1st fix install there will be one or more 125mm pipe/s protruding down below the ceiling datum, or occasionally through a wall. Assuming these pipes penetrate what will become a finished surface, your plasterer must cut a hole in the board before offering it up, so the pipe is still visible after the skim. Ideally the plaster will seal around the pipe to prevent air escaping into the void behind. The pipes are cut flush with the finished ceiling at our 2nd fix ahead of the final decor.
NB: If the plasterer in any way boards over the ceiling plenum, or removes ducting to facilitate their work, the only way to fix this ‘snag’ is to remove the ceiling.
