AIR-TO-AIR OPTIONS
this unit can also be used for space heating if the heating demand is exceptionally low. Very accurate heat loss calculations will need to be done and the system will need to be very well designed and installed to ensure that it can indeed cover the heating requirements or it may call for heat from a back-up electrical heater that could end up costing a small fortune to run.
How much will this system cost?
Expect to pay around £1,200 for a simple version of a EAHP product, with costs rising to around £2,000 for newer units and even as much as around £3,000 or £4,000 for units with more connectivity and control. These costs do not include installation.
Retrofit solution
There are also ‘retrofit’ versions of these exhaust air heat pumps that do not have a hot water cylinder attached. The fan unit instead goes in the loft, or near the cylinder, and you run ducts from the bathroom and other wet rooms, as well as the route to outside for the stale, cold air, and then plumb it to the cylinder, most often in a parallel system. This means that the EAHP only heats the water which is in the cylinder — by pumping water between the cylinder and the heat pump.
Before you buy any system, check with a local heating engineer that it’s compatible with your existing cylinder and plumbing arrangement.
How much will this system cost?
These retrofit exhaust air heat pumps can cost as little as around £900 with more complex units going upwards of £4,000. Make sure you also factor in any remedial plumbing and electrical works required to connect it to existing cylinders and controls.
Micro heat pumps are also available as air-to-air systems rather than the air-to-water options. The air-to-air units are often made to work with a MVHR unit and they are also commonly only able to do cooling. The cooling box is normally installed on top of the main MVHR fan unit and this effectively makes it a taller box. The unit extracts heat from the fresh air going to the rooms and dumps the heat in the stale expelled air. Some of these units can also be reversed so that heating and cooling options can be used but they are not easily retrofitted and should be planned into the ductwork design when the system is initially designed.
“Air-to-air systems are best suited to low-energy homes such as Passivhaus builds”
Heating and cooling solution HEAT PUMP BUDGETING
There are also micro heat pumps that have been factory built into MVHR systems, and these are often referred to as heat pump ventilation, and they can do both heating and cooling. The heating and cooling function is done while the air is being delivered to the home so that indoor temperatures can be maintained.
Due to the low energy delivery, these products are best suited to very low-energy homes such as Passivhaus builds because, ideally, you want to deliver the heat in the air that is required for the healthy existence of the occupants of the home. In any other property, the heat delivery may not be adequate to maintain comfortable temperatures in the home because of the air tightness levels and the higher heat loss. There is only so much heat that air is able to hold so if you need some extra heat then you will need to increase the air speed and that may, in turn, increase the risk of noise. The ductwork all needs to be insulated to prevent heat loss in winter and also to prevent condensation in summer when cooling is required.
There is a valid argument that if you fit one of these systems you may not need a wet heating system and therefore the cost is offset by not needing the alternative heat generator and wet emitter system such as underfloor heating or radiators. Just make sure that the design calculations have been done with your expectations in mind and that you fully understand the type of heating system that you are investing in.
Many MVHR installers are now fully versed with cooling options and you will need the MVHR installer to insulate the ducts. Duct insulation is not something that you want to add after the MVHR system has been installed.
How much is this system likely to cost?
The add-on cooling units for MVHR systems are usually not cross compatible between different manufacturers so prices for these differ between manufacturers but expect to add around £3,000 to £5,000 for the cooling unit and also an additional cost for the insulation required for the delivery ducts.
Duct insulation ranges between £6 to £35 per metre, depending on the insulation quality and the duct diameter, and don’t forget the cost of installation of the insulation.