Home Ventilation - Separating the Salient from the Sales

Forums › Home Workshop DIY › Home Ventilation - Separating the Salient from the Sales - Your thoughts?

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pctek

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#887807 1-Sep-2013 15:12

Slumlord: Thanks. Yep, I only need ventilation - trying to prevent condensation and moisture build-up. Not worried about heating.

So eliminate, or at least reduce, the moisture in the first place.

This place had an HRV when we bought it, irritating thing would turn on by itself, we found after accusing each other of turning it back on.
We disconnected it which reduced the power bill, stopped the filthy rings around the vents in the ceiling - and the coughing for those with dust allergies - and we have no condensation problems.

This is a standard modern, aluminum window house....but we do have at least 2 windows open a wee bit in Winter - and pretty much all of them in summer.

mattwnz

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#887848 1-Sep-2013 17:20

timmmay:
mattwnz: The components to buy these things are reasonably cheap, so there are pretty big margins in them. My parents have a ventilation system in their house which they had installed for them years ago, and it is hopeless. Their house is big with lsome skillion roofs, and I think they really only suit houses with pitched roofs with a large roof space. Not to mention that in the winter they are often pumping in cold air from the roof space, often where the fibreglass insulation is. You can feel the coldness of the air coming in.

Read up on the system I posted about. It doesn't use air from the ceiling cavity, it uses fresh air, passes it through filters, and then warms it with the stale air it takes from the house - in summer it cools it if the air inside the house is cooler than outside. The idea is the air quality in the ceiling cavity isn't good, and stale (warm moist) air has heat that is recovered. You can put an input in the bathroom over the shower if you want to as well, though it won't be powerful enough to get rid of all the steam. It recovers 80% of the heat that it draws out.

You can also run them on a timer, or thermostat.

It depends on who you speak to as to whether bring in air from the outside is a good idea, over bring in air from the ceiling cavity. The problem is getting good independent advice which isn't tied to any system. But IMOH a ventilation system shouldn't be needed if people open their windows and eliminate other problems, such as rising damp from subfloors, insulation, thermal breaks in windows and double glazing, etc.

timmmay

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#887867 1-Sep-2013 18:15

mattwnz: It depends on who you speak to as to whether bring in air from the outside is a good idea, over bring in air from the ceiling cavity. The problem is getting good independent advice which isn't tied to any system. But IMOH a ventilation system shouldn't be needed if people open their windows and eliminate other problems, such as rising damp from subfloors, insulation, thermal breaks in windows and double glazing, etc.

Agreed, to a point. I have no rising damp as I have ground sheets and under floor insulation, I have great extraction, and I have security stays on the windows so I can leave them open. That helps, but I feel that forcing air in does provide better ventilation, gets rid of more moisture, and generally helps keep the house drier. In winter on sunny days bringing air down from the ceiling cavity does warm it up a couple of extra degrees, and every degree helps reduce heating costs.

In the ceiling cavity I have wool, I have pink batts, there's old mouse droppings (under the insulation), there's borer treatment, old hessian, there's 50 years of dust and general crap up there - to the point I'm considering vacuuming the whole place.

Bringing in air from the outside gets rid of all that, with the downside of pollen and potentially smoke from fires. That can probably be filtered out to some degree. You can also use a heat exchanger to warm the air. This pulls air out of your house though, so I'd want a system that I can program easily, especially to have it power down at night, or at least run on very low speed.

Overall I think outside air is probably generally better for my house, but maybe not for everyone's.

martyyn

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#888163 2-Sep-2013 10:45

We finally bit the bullet and had an HRV system installed last week. The A6 system was initially quoted as $4600 and we were offered a reasonable discount on the spot.

I cant tell you what we eventually got it for but our condensation problems were solved in 24 hours and the house is definitely dryer and warmer because of it.

The thermostat in the wall unit is a little optimistic with the temperature in our hallway I feel and you can certainly here noise if you stand under the vents and listen for it, but just doing you normal thing you don't notice them at all.

So weve had a DVS in our old house and an HRV in the new one and they have both cleared the condensation in 24 hours but I have to be honest, cost was the only driver in our decision. They've both done exactly what I'd expect of them.

Batman

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#888212 2-Sep-2013 11:49

how many vents for that price?

timmmay

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#888217 2-Sep-2013 11:57

Was it a proper heat recovery ventilation unit, or a branded unit that's basically just a big fan? What make/model?

martyyn

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#888254 2-Sep-2013 12:53

Six vents and what looked like two 'units'. I didn't pay enough attention to see what it was they installed. To be honest, it got to the point where I couldn't care less.

I got fed up with salesmen either just outright lying, having every website and forum telling me great things about whatever it was someone installed or the evangelists just telling me it was as easy as opening a window. It was information overload with little direct comparison.

In the end I thought, sod it. I'll go with the HRV guy who lied the least and in the end the deal they offered was too good to refuse. The system has worked. We have a warmer, dryer house so I'm moving on to worry about something else now :)

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mattwnz

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#888295 2-Sep-2013 13:45

timmmay:
mattwnz: It depends on who you speak to as to whether bring in air from the outside is a good idea, over bring in air from the ceiling cavity. The problem is getting good independent advice which isn't tied to any system. But IMOH a ventilation system shouldn't be needed if people open their windows and eliminate other problems, such as rising damp from subfloors, insulation, thermal breaks in windows and double glazing, etc.

Agreed, to a point. I have no rising damp as I have ground sheets and under floor insulation, I have great extraction, and I have security stays on the windows so I can leave them open. That helps, but I feel that forcing air in does provide better ventilation, gets rid of more moisture, and generally helps keep the house drier. In winter on sunny days bringing air down from the ceiling cavity does warm it up a couple of extra degrees, and every degree helps reduce heating costs.

In the ceiling cavity I have wool, I have pink batts, there's old mouse droppings (under the insulation), there's borer treatment, old hessian, there's 50 years of dust and general crap up there - to the point I'm considering vacuuming the whole place.

Bringing in air from the outside gets rid of all that, with the downside of pollen and potentially smoke from fires. That can probably be filtered out to some degree. You can also use a heat exchanger to warm the air. This pulls air out of your house though, so I'd want a system that I can program easily, especially to have it power down at night, or at least run on very low speed.

Overall I think outside air is probably generally better for my house, but maybe not for everyone's.

Systems that take the air from the cavity are still essentially getting the air from the outside via gaps in the roof, but supposedly it is getting warmed a bit by the existing air in the cavity, as well as by the sun during the day (a bit of a crude system). Branz has written some articles on them, and they suggest using a heat exchanger if getting air from directly outside. http://www.branz.co.nz/cms_show_download.php?id=1c2a51c5310206e92ee4ae2222bcf72eb4b0646f & http://www.branz.co.nz/cms_show_download.php?id=5e2e00fa467bdd16ceebbeac289916d63609a57ahttp://www.branz.co.nz/cms_show_download.php?id=5e2e00fa467bdd16ceebbeac289916d63609a57a
Personally I would be a bit concerned about these system sucking up lose or disturbed fibre glass particles from older insulation, which are very fine, and possibly wouldn't get stopped by filters.
This branz appraisel is quite interesting http://www.branz.co.nz/cms_branz_show_appraisal.php?id=269%20
It says that hey work better in newer houses which are more airtight, rather than older ones which are more 'leaky' and have more gaps, were the results can be unpredictable. But I would have thought it was the older houses that have more problems with condensation.

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#888309 2-Sep-2013 14:10

hmm interesting!

Skolink

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#888317 2-Sep-2013 14:42

martyyn:
In the end I thought, sod it. I'll go with the HRV guy who lied the least and in the end the deal they offered was too good to refuse. The system has worked. We have a warmer, dryer house so I'm moving on to worry about something else now :)

If others are considering the same decision I would recommend neither HRV(brand) nor DVS. A portable dehumidifier is less expensive to buy, and cheaper to run*.

*In a home that requires heating to maintain a comfortable temperature for a significant portion of the year.

timmmay

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#888319 2-Sep-2013 14:47

Skolink:

If others are considering the same decision I would recommend neither HRV(brand) nor DVS. A portable dehumidifier is less expensive to buy, and cheaper to run*.

*In a home that requires heating to maintain a comfortable temperature for a significant portion of the year.

A dehumidifer is pretty small scale, and with house windows open you're trying to dehumidify the planet. The fans on a decent ventilation system pump through a lot more air, they warm (or cool) the air in the house if it's set up correctly to get air from the ceiling cavity or using a heat exchanger. They should be cheaper to run as well, as they're just a fan, and reduce heating costs by driving out moisture that doesn't need to be heated. I don't leave mine running 24/7 as they blow cold air into the house, it's on during the day, and I have it on a timer so it comes on occasionally in the evening for short periods to keep the air fresh after there's been people inside for hours with the windows closed.

I don't think a dehumidifier can replace a ventilation system, though there is some overlap in their use in some cases.

Jaxson

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#888320 2-Sep-2013 14:54

This has been discussed many times here before, but basically there are pros and cons to every approach you want to take.

A stick hut with see through walls would offer an extremely well ventilated property, with little condensation issues, as the warmer humid air from breathing/cooking etc would be cleared from the room very easily. This house would cost a huge amount to heat, as the design offers no attempt to retain any heat.

Conversely living inside a sealed refrigeration container would offer excellent heat retention properties, but the air would become very stale quickly. The air would be very laden with moisture, but condensation probably wouldn't be an issue given the absence of many cold surfaces.

Fundamentally a forced air system is a draft that you are paying for. It's a system that takes outside air and pumps it directly into the house, feeding in straight past any insulation you have installed etc. Where they attempt to correct this via an element to pre heat the incoming air, well you're just going to have to pay a lot to run this over winter. Certainly the heat exchanger approach is probably the best option in this situation.

One should also do a bit of thinking about air flow paths. If you have air being forced into your home, it will need to find it's way out again. If all your house windows are closed, it's probably being forced back up into the ceiling cavity via downlights, or out existing vents, such as range hoods or shower extracts. Grill placement in a room is probably worth considering so you ensure the air flow path does cycle the rooms air, rather than it shooting directly out in the nearby hallway etc. Modern homes seal extremely well, where as older homes will leak around windows etc, and probably have a more efficient air turnover rate because of that.

timmmay

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#888325 2-Sep-2013 15:01

Systems with a heat exchanger rely on careful duct placement. Fresh air is bought into the home through the heat exchanger, flows where it's meant to, and then sucked out by another fan. This exhaust goes through the heat exchanger to warm (or cool) the incoming air with 70-80% efficiency. If you're putting through a large volume of air there will be significant heat loss, but a lot less than a simple fan that just lets the air go out through cracks in the floor, around windows, etc.

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