Consumer welcomes the results of the Otago University study on the heating and cooling potential of roof space air.
The myth of abundant free heat in the roof space is well and truly busted.
The Otago university study has monitored the roof space temperatures in kiwi bungalows (with the classic corrugated iron roof) and found that pumping in air from the roof space could often make your house colder in winter and hotter in summer than the usual inside temperature during those seasons.
For some time now Consumer has been concerned about the way some ventilation systems are advertised. It may well be hot enough to grill a sausage on a corrugated iron roof in February, but that’s not when homes need extra heat.
This study proves Consumer is right about heat in the roof space. We have been saying for many years on our website that “there won't be warm air up there on frosty nights and cold grey winter days”.
Consumer looks forward to the end of advertising that makes misleading claims about the heating or cooling benefits from positive-pressure type ventilation systems. These ventilation systems should only be promoted on their ability to control condensation by providing adequate ventilation.
Condensation is a problem in many older house designs in New Zealand, and ventilation systems have been shown to reduce condensation in many types of houses.
Ventilation systems which use roof space air should not be advertised on their ability to provide winter heating or summer cooling in New Zealand houses. They also shouldn’t be promoted on their ability to control dust mites as an earlier study by the Wellington School of Medicine and Health Sciences showed no reduction in house mite numbers after ventilation systems were installed.
All three claims are now proven to be misleading.
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My husband is working for HRV in Hawkes Bay and so he agrees that the system only provides the Free Heat when nature can give it to us. Your roof is a giant solar collector so it makes sense to use the free heat from the sun on bright sunny days. On a normal day the roof could be 24 degrees and your coldest bedroom could be as low as 13 degress at midday. Ben said that The World Health Organisation wants us to maintain 18 degress if possible, a well ventilated home will retain heat longer than a wet home and per m2 an HRV is good value as it treats the whole home.
Ben said you will still need a heat source during the night as the system is controlled by nature.
Our experience is that condensation is very effectively removed in winter. You can also 'manage' the flow in the winter by manually adjusting the thermostat to pump in air when there is more heat in the ceiling than in the house, even when this is less than ideal. i.e. you may want 21 degrees but have to settle for pumpming in at the ceiling temperature of 12 degrees when the house is 9 degress and the ideal is set at 21 - just watch out for chill factor in the immediate area around the ceiling fan(s). Less moisture certainly improves the living conditions.
Our Smart Vent system has a summer feature which takes cooler air from outside and pumps it into the house in summer, in winter it pumps roof space air and I agree that there is no warm air up there, you can see this on the display the day you install it, outside temp matches ceiling temp the moment the sun is gone
I had a Healthaire system, and it was programmed to turn off at 23oC which meant that I wasn't getting hot air down from the roof in summer.
A very simple roofspace fan, timer, and thermostat,helps to heat the remote, colder areas of my house, which are not within range of my woodburner.
It is only effective on sunny days, from around 10.30 AM, but in sunny Hawkesbay, it works very well, at a minimal cost.
This is almost free heat, within limits, but still of value.