Home Ventilation Systems and Heat Transfer Systems

A lot of customers have many questions about home ventilation and heat transfer systems. I shall try to answer the most common questions here. If you have any questions I have not covered here you are more than welcome to contact me here or by phone.

Question: Will a home ventilation system stop my windows from condensating?

Answer: Home ventilation systems will reduce the amount of moisture in rooms where outlet vents are located. Outlets are typically located in bedrooms, living rooms, hall ways & dining rooms.

   Creating positive pressure in these rooms (forcing air into a room) will work against cold, damp air drafts that typically enter through gaps in window & door frames making the room feel warmer & dryer.

Question: My kitchen, laundry & bathroom also condensate can I have outlet vents in these rooms?

Answer: Kitchens, laundries & bathrooms should be regarded as air extraction areas only. These rooms typically produce moisture that is trapped in the building envelope, this is particularly true of more modern buildings that are better sealed than draftier older homes. Using a range hood whilst cooking, ducting the clothes dryer exhaust outside & using a bathroom extraction fan that delivers 10 to 15 air changes in the room per hour should remove this moisture. It is also a good idea not to dry clothes on racks inside the building as this moisture will condensate on windows and be soaked up by soft furnishings such as carpets, settees, bedding & curtains.

Question: What are the other sources of moisture in my home?

Answer: One of the other sources of moisture are people. On average we loose about 400 ml of water per day through our breath and 200 ml of water through perspiration whilst sleeping.

This moisture is absorbed by warmer air but when temperatures drop colder denser air is unable to absorb as much moisture. This is why windows in living areas & sleeping areas condensate & soft furnishings feel cold & damp.

Question: I have had a home ventilation system installed but my bedroom windows are still a little condensated in the mornings, why is this?

Answer: As time progresses from the installation of a home ventilation system the furnishings in the rooms with outlets will become dryer and dryer as the moisture contained in them evaporates this may take a full summer season to complete.

Question: My home ventilation system blows cold air into my room during the early hours of the day &  there is still a little condensation on my bedroom window in the morning.

Answer: With the SmartVent Positive Pressure home ventilation system that Thornton Electrical install there is a minimum air intake temperature that can be set so to that the fan will reduce in speed or shut off when this minimum temperature is reached. Competing home ventilation systems such as HRV do not have this option.


Once the ambient temperature starts to rise again & the roof cavity starts to increase in temperature the SmartVent system will increase the speed of the fan drawing in the warmer air from the roof space & remove any condensation on the window. If the SmartVent system is programmed to stop the fan at the minimum set temperature the system will need to be turned back on in the morning.


Often people confuse the system with a heating system which it is not. It is better to put another blanket on & have the system running than have it switch off, a damp room in winter feels colder than a dry room winter. Outlets are not placed over beds in order to reduce the feeling of air movement. The ideal setup for the system is to start of with the minimum shut off temperature at it lowest setting and slowly increase it night after night until condensation just starts to appear. This can be done by the owner and does not require an electrician.

Question: Will a heat transfer system work better than home ventilation system at reducing the moisture in my home?

Answer: Whilst a heat transfer system is a cheaper option than a home ventilation system it will only be effective when the heat source in the inlet room is operating, generally people do not start their fires or run their heat pumps until the evening meaning that condensation in the outlet rooms is not removed at the start of the day & can be absorbed by soft furnishings or even remain on the windows, creating mold & damp. However a heat transfer system is a great addition to a home ventilation system.



Question: Should I consider a heat transfer add on for my home ventilation system?

Answer: A heat transfer system can only be installed if the heating system is compatible. Compatible heating systems are:

  1. Pellet fires

  2. Wood fires

  3. Electric heaters

  4. Heat pumps

These heating systems will work well with a heat transfer system as long as the heating system is capable of producing heat that exceeds that required for the room in which it is in. Owners of heat pumps should get the output sizing of their heat pump checked first as it was probably only sized to heat the room it was installed in and not an additional two or three bedrooms.​

Heating systems that are not compatible are:

  1. Portable LPG heaters

  2. Un-flued fixed gas heaters

Flued gas heaters should be inspected & checked by a licenced gas fitter, with a statement in writing issued that the gas appliance is suitable for use with a heat transfer system​. This is because gas appliances produce a lot of moisture, when they are un-flued or the integrity of the flue is not 100%, moisture will enter the home along with gasses from combustion. When gas is burnt moisture is produced along with carbon monoxide if the flame burns yellow, the later can cause asphyxiation, not something you want in your bedroom whilst sleeping if the gas fire is still running.



472 Maitai Valley Road Nelson 7010 NZ