Room heat recovery. Can it work?

With more and more people getting worried about heating bills one of the ways that is being highlighted to reduce costs is to use a heat exchanger on any ventilation systems. Basically they are designed to work as a way of using the warm moist air to preheat the cooler incoming fresh air by using a heat exchanger. This all sounds great, however at around £300 for a room based system do they work?

The basic answer to this is ‘it depends’. Really helpful I know. To get to the bottom of whether it is right for you, you need to know the answers to the following points / questions.

1. Which wall is the extracted air being expelled?

2. Does the extract require a filter? (normally associated with a kitchen extract)

3. How airtight is the room in question?

1. The direction that the wall is facing makes a huge difference to its effectiveness. All extracts have fins on them that are designed to open when extracting air, however they are no match to the power of the wind. So if they are facing into the wind they will just be blown shut and hence stop the whole system working (this applies to all extractors, not just heat exchanger ones). So look to site your extract on an east facing wall or into a well vented roof void / eaves.

2. If you are extracting air from a kitchen area then you will need to have a good filter system to stop the sensitive heat exchanger from blocking up. So you will need to be prepared to have a good maintenance regime in place so that it can work effectively.

3. If your room is not very airtight then one must question the effectiveness / need for a heat exchanger as much of the air being lost / removed will not pass through the exchanger and so any good that the unit does will be quite minimal compared to the rest of the ventilation going on.

In conclusion I think that you should only look at investing in a room heat exchanger in the following situation:

Bathroom with an east facing / eaves extract that is well draught proofed.

I would also suggest that your driving force is not money saving, but to create a more comfortable environment when showering / bathing.

Heat exchangers are great in airtight new buildings, but they use is really limited in older homes (unless a major refurbishment is undertaken) and in this case you will be looking at a Whole House Ventilation System.