I touched on DVS systems in my last blog and I will go a bit further today.
There are two systems that can take warm dry air from the roof space and pass into the home via ceiling outlets. The generic names are Domestic Ventilation Systems (DVS) or Home Ventilation (HRV). Do not get confused though with Heat Recovery Ventilators (HRV) which take warm moist air from the house and via a heat exchanger replace it with dry slightly less warm dry filtered outside air.
I will from now on call the DVS and home ventilation systems, which are the basically same product, the general name of DVS. These are also known as Positive Pressure Ventilation (PPV).
During a sunny winter’s day the roof cavity can get hot with the sun shining down on it. Clay tiles do not make the roof cavity hotter for longer than a metal clad roof and take longer to warm up.
What a very basic DVS system does is blow this warmed dry air via a filter into the house. This dry air pushes out, via gaps in windows and doors, the moist air caused by breathing, washing, cooking, etc.. Buying a dehumidifier to cure a moisture problem is useless as you are only getting rid of the symptoms of the problem not the cause of it. They have to be constantly emptied and are only reducing moisture in the area they are situated in. They also cost more to run than a basic DVS system, which is just a fan. Some people have found that they have had a reduction in their heating bills after fitting a DVS system. This is because it can warm up a home for the cost of just a fan running and it is easier to heat up dry air than moist air, as there are less water molecules in the air to warm up. Other benefits air that the air is filtered and can reduce asthma and allergy problems. If there is positive pressure inside a house there is less chance of pollens coming in. The most obvious addition to the system is to have a heater that takes the chill off as the air in the attic space cools down at night or on none sunny days. In most systems the heater just makes the air from the attic the same as the room temperature at best. With the system from Moisture Master you can have a 2kw heater, which on the highest setting actually blows hot air, but not enough to heat a house.
If you have got a pellet or log fire there is normally an option to take very warm air from near the fire and pump it around the rest of the house. This is a very low cost option as the whole house can be warmed up at the cost of running a fan. Obviously there is a thermostat that switches between the attic air and the ‘fire’ air depending on temperature. There is also a system that moves air from the fire area to other rooms. This only really works when the fire is going and for the price you would be better off buying a DVS system which can supply dry air all year round.
The last option is the summer option. This takes cool air from the South side of the house and blows it into the house. You could go out on a cold morning and shut all doors and windows tight and later the weather changes and your house starts to become hot and stuffy. With the summer option as the house gets too hot cool air is blown in and reduces the heat almost as if you had a window open.
The shape and size of your home and your family’s needs dictates how many outlets you have. As I have a long house I chose to have two outlets in the bedrooms furthest from the heat pump and one in the lounge at the other end. It is important to remember that these systems can give benefits even when there are no other heating or cooling systems in use. So if you are in Australia for 2 weeks in the winter you can come home to a freezing house. All the static air in cupboards and behind furniture, especially on the south side of the house, has come down in temperature to near the outside temperature. This cold air on your return can take several days to warm up. With a DVS system running, warm air on sunny days has been pumped all round the house and kept the overall temperature higher than it would have been. So do not rule out having an outlet in the area near a heat pump as you may not have to turn the heat pump on depending on how big your heating element is.
With any system that draws fresh air from the roof cavity or outside, which is then passed into the home, there could be a smell in winter, if you live in an area with lots of log fires. If you step outside your door on a winters night and you catch the sweetish aroma of smoke, that smell will probably be drawn into your home.
I have the Moisture Master system which has an automatic mode, but allows you to control the heater temperature and fan speed. So on a cold day I can turn the fan down to half setting and turn the heater up to the highest setting and nice warm air flows into the house. You must not have the fan setting more than the heat setting otherwise the air will not have had chance to warm up as it passes over the heating element. At night we turn the heating down to half and the fan to the quarter setting just so that the chill is taken off the night air. On hot days we have the fan on full so that cool air is blown in whether we are at home or not. On several days last year we had the system set to auto and with the heater on. Later during the day the sun came out really warmed the house up and the system swapped over to cooling.
If you suffer from ‘crying’ windows, thinking of buying a dehumidifier, constant cold hands even when the heat pump is on or damp and mould, a DVS system could be for you. There are various options so get various quotes and go for the option that suits you best. Money should not come into the equation as they could save you money and fitting extras later could be a lot more expensive. I saw a lovely expensive house with varnished wood everywhere; because of crying windows a very large internal wooden window sill had rotted. To replace that sill will cost more than a basic DVS system. Talk to people that have one and see what they reckon about it.
Remember with one of these installed can make your house more resalable.
Does anyone know where to buy arizona 5 filters not HRV as I don’t like the black mail sales pitch. You ask them how much for filters, first thing they say is your warranty will be void if they dont install at 2 year yeah right smart arses cheers warren alttruck@xtra.co.nz
Checking out ventilation systems. If I use a HRV it would blow warm air into house, But it would be more humid than the air in my house. House humidity is about 45% in roof space cause it mid winter it is 86%.
So why would I want to replace with more humid air, admittedly it is warmer by a couple of degrees but is much more humid.
The figures seem really odd. Why should the roof space be that humid. If this was the norm roofs would be collapsing all over as the wooden supports would be rotten.
Hi Steve,
Its a concrete tile house,only about 30 year old.Up top is good dry,no smells at all.Good insulation.Had the roof sealed and treated about 5 years ago.A concrete tile roof house has heaps of air ventilation,my thoughts it would be as humid as outside.
I found this site so useful when trying to decide whether to have a leap of faith and purchase a HRV system. I live in Dunedin and condensation was an issue in the house. The rep was OTT and I think the product is expensive but as far as removing condensation it has been superb. I was never ‘sold’ this product as a heating device- but it has raised the temperature by 2 degrees in non heated areas on a cold day- and on sunny days by many more degreees. So overall I am thrilled with the result. It also removes cooking odours.
Relative humidity is associated with heat. Heat mobilises moisture in the air and raises the RH.
You heat a home it mobilises the moisture into the air, this is a prime opportunity to flush this moisture laden air out with a good PPV consequently conditioning your home and over time making it drier.
On a cold morning the air inside the home will be cold and the RH will be low. This is a false sense of security regarding moisture in the home. The moisture at that point has settled and or soaked into the home fixtures and furnishings.
You can see the the RH in a home change from 55% RH at 8am to 80%+ RH by 12. Sometimes the RH in the ceiling will be high when it heats up but this is caused due to the condensation formed in the ceiling on a cold night. This moisture mobilises when the ceiling heats up creating a high RH, it is not there for long and soon dissipates as the air in the ceiling is replaced and expands. Once this moisture laden air is gone from the ceiling, any fresh air which is heated will have a much lower RH than outside or what is in the home. It is this drier warmer filtered air which is flushed through a good PPV which helps keep your home drier with an average lower moisture content.
There are some good down to earth FAQ’s at the Sayr website:
http://www.sayr.co.nz/FAQs/tabid/30620/Default.aspx
Recent testimonials:
http://www.sayr.co.nz/TESTIMONIALS/tabid/32569/Default.aspx
Check out some down to earth FAQs and recent testimonials on a good PPV
www sayr co nz
Are the upvc double glazed windows here fitted with air vents in the frame as they are in the UK? This does allow some air flow.
I Have a weather station that reads humidity and temp inside and outside.Cheap as it is ,i think it is fairly accurate.
The lower the temp the higher the humidity,inside and out.Thats what it tells me anyway.
Currntly the outside unit is in ceiling space.It is as humid there or near enough to outside.
So why on earth would you want that air in your house?.A couple of degrees warmer sometimes sure but a lot more moisture in the air?
Any comments on pellet fires appreciated.I live in christchurch and thinking of getting one.
People say they noisey,i go to showroom quiet as,no worse than heat pump.They say older ones are noisey.
One person said his is 3 years old and sounds like a hellicopter?.How can this be?
Is it just because they need maintenance( bearing etc).That maintenance never done?.After all you need to service a heat pump regularly,I never done mine.
The ones I saw have a constant tinkling sound as the pellets are dropped in. Having had an open fire in my childhood and almost jumping out of my skin when a log has let out an almighty crack they are not too bad. Our heat pump is quite loud, but as it is a constant drone in the background you tend to forget about it.
At the showroom ask them to turn it up to full and see what they sound like when working at their hardest.
Kevin. You need to be monitoring the RH in the ceiling on a constant basis and see what it averages at over various times/temps/conditions.
Also you need to be reading the RH inside the house when it is warm, thats where the problems come from with damp homes. Again, if you are reading gauges you need to be extremely thorough in recording and calculating data. It is too easy to be mislead with a couple of readings and making ill informed or uneducated conclusions.
I’m not sure what the sales people told my parents; i just know that despite the fact i agree it’s somewhat false advertising? It half works for people that have asthma; we’ve seen significant amount of reduction in molds (sorry i spell it without the U, i’m american
) – and other condensation problems. I think the new housing idea is not sound, cause you also gotta look at the city you live in.
Any true person would know that Central Heating, PLUS one of these Heat Recoveries, and maybe the other bits would make it ideal – BUT because we all live in New zealand, it’s enough just running a fan heater to cause a 400 dollar power bill.
Being that i have mild to severe asthma depending on the time of year and the allergic issues i have, the HRV has even made living with a dog (which we all know that asthmatics SHOULDNT have long haired shedding adorable horse-like puppies whom slobber on you at ever chance! XD) more tolerable.
Yes; i think there’s things that every system goes wrong with- i just know that what we have (Yes a branded HRV, which may or may not be true to it’s form) works as well as it can. Burnt Toast in our house because it’s SMALL, works over a period of time.. and frankly it doesnt serve when you leave your bathroom door open to serve the house the nasty smells after someone’s been eating curry. (So burnt toast mode is totally not going to fix that
)
All in all i think the one we have may not BE the best, but it works for what we paid for it, without spending an arm and a leg on power that is.
@ janie 18 July: Hi Janie. I’m not sure about the uPVC window manufacturers, but some of the aluminium fabricators can include trickle ventilation in the frames.
Our company – Easy Air – has been manufacturing and supplying glazed-in trickle (passive) vents for the last 13 years. Our vents can be fitted in to new windows (we also have a double glazed model), and they’re the only ones on the market here that can also be retro-fitted into existing windows.
Trickle vents are standard in the UK, and are very effective at controlling moisture levels.
Positive Pressure Ventilation is not common over there. In fact it’s not even recommended in the building regulations, whereas passive is.
@ Kevin: Hi Kevin. Great idea setting up a humidity meter in your home before making any decision on which ventilation to choose. I’m surprised more people don’t do that, along with taking temperature readings in their roof space before selecting a ventilation option.
A quick note on Relative humidity vs total humidity. Cold air has the capacity to hold much less water vapour than warm air. Relative humidity is the measure of the actual water vapour RELATIVE to the capacity of the air to hold water AT THAT TEMPERATURE.
So, cold air with a high RH%, will actually have less moisture than warm air with a lower RH%.
As an example: If you draw in 10C outside air with 80% RH (approx. 7.2 g/m3 of water) and warm it to 20C, the RH of that air has now dropped to approx. 42%RH.
So you can see that drawing in cooler air and warming it, at the same time displacing the old damp inside air continually will lower your total levels of water vapour.
Hence the standard recommendation to continually replace inside air with fresh outside air.
I hope that helps
I first heard of Sayr when researching opinions in these type of forums. I got one and now it’s my turn to give them a plug. They’re a smaller coy for sure but have proven themselves equal and surpassing the big boys as far as I’m concerned. More than matched them in features and result. Well done guys, I’m telling others like I said I would.
hi all
going back to some comments earlier re musty odours. We had an HRV installed at the end of last summer but althought the air is drier we have definitely noticed an unpleasant musty/dusty smell which is intensified when the system is actively pumping air. I have complained to HRV (whose after sales service was appalling but that’s a different story) who moved one of the units as they said the front of the house (which is newer, ie 10 yrs old) had an odour which newer rooves sometimes do. Now that it is warming up again we are really noticing the odour as the fan is working harder. Am really reluctant to fork out hundreds of dollars more for further ‘carbon socks’ or whatever – any suggestions? HRV didn’t seem to have any ideas; we are going to go back to them but want some ammo first!
Hi Mares
Hmmm. Not a lot you can do. These musty smells generally are from 1 or 2 reasons.
1. You have building paper under the roof material and when the roof heats up, the building paper material gives off fumes which most of the time is the ‘tar’ in the paper.
2. You have insulfluff in the ceiling as insulation. This can be old and under any new insulation. This insulfluff stinks.
Sometimes these odours are exaggerated from a low roof? nothing you can about that apart from making sure the unit is hung as high as possible in the apex of the roof.
There is not a lot you can do without spending more money other than the carbon socks.
The smell will diminish in time but it could take quite a while.
This is not ‘common’ but it does affect some houses.
Definately go back to hrv. Good luck and let us know how you get on.
An HRV convert here . We have a 1929 weatherboard house with large roof cavity . Our house now feels like it has much nicer air and is much more comfortable . Is definitely warmer and drier in the autumn and spring evenings after fine days ( need log burner on less ) . Not so much different in winter , but we never expected it to heat the house anyway . Burnt toast option is great . No problems with smells or noise . Have since psuedo – double glazed ( over leadlight windows etc , great system ) and that has helped also . Pellet burner noisy , ( is an older model ) , by making an irritating whine , but heats OK . Pyro-classic log burner is what keeps us toasty in the ChCh winter , and we cook on it too. Brilliant . !!! . I would recommend an energy action report ( $100 ) to anyone who is considering spending money on heating/ventilation , as what works best depends entirely on age/construction/materials/ location of house . Not all systems work well everywhere .
First of all great article!
Theres many comments and opinions on here and many other websites with regards to home ventilation. Some are true but many are not, the only real fact is every house is different and a unique system should be designed for each property.
For this reason it is important to actually get a trusted consultant around and go over the property properly, otherwise people end up with situations like the couple on Target the other night when they installed an HRV system. HRV home ventilation
More to the point people considering home ventilation especially in the Nelson area should feel free to contact me and Ill be more then happy to answer their home vntilation questions. Visit my website http://www.haveahealthyhome.co.nz for more details.
I am amazed at the information on this it has been very interesting, thanks everyone for the comments …. My husband and I had an older home 1960 style with all the ventilation problems damp and freezing cold ice on the windows in the winter after a frost, we are in the southland area, we put in insulation ceiling and underfloor, an HRV with a log fire and eventally a daikin heat pump, the biggest floor model … the last 2 winters we would get up in the morning and couldn’t tell there was a frost until we went outside it was so good, the HRV had a huge impact and the heap pump just toped it off by giving that extra warmth it heated the whole house with the HRV helping to spread the heat around the other rooms, it was amazing, I also no of a person who trialed the HRV in there home, liked it so much they also put it into their 2 rental properties over time, they find it amazing as do their tenants, I was researching what is best now which is what bought me to this site and I have read all the comments, I am sorry to those who find the HRV not to their liking, for some reason it is not working in your homes as I have known it to work and have had it work in our home … we now have a new home and after reading this and other research we will install another HRV in our new home, which is only 6 years old but damp and musty after being in here only 2 days I can’t wait to get the ventaltion system in, i do hope they can do it quickly I feel I am getting sick, the bathroom and toilet area also smells of mould … The house was beautifully cleaned as we moved in but it still smells of mould … Good luck everyone … HRV is the one for me … ;o)
Just adding my 10 cents worth. I’ve had an HRV in the past and it did a really good job. But I bought a SAYR last year. Same motor so it’s as powerful and has some really cool features. It’s cheaper, but thats not why I bought it.
It’s the fact you get cooler nights in summer when your sleeping that I like!
Hallo everyone,
) I am much into insulation and am replacing all my windows with double glazed thermally broken suits. Underfloor insulation will follow.
a lot of people with a lot of knowledge and ideas, maybe someone has one for my situation as well?
I bought a 35y old lockwood house (so yes there is no roof cavity) and do not want to crack more holes in the ceiling or walls than necessary.
I got one bathroom extractor fan and a heatpump and thinking of replacing the fan with the outlet of a gas or wood fire (needs to be fed through a interior wooden wall). I will then need another way of moisture extraction out of my two bathrooms (one of them has no extractor at all). My thought is a heat transfer system that will take out the moisture as well and replaces the air with either dry warm air from over the burner (or from close to the heatpump) in winter or cool dry air from under the house in summer as I have a lot of room under the house that I can use.
Since I am German as you can tell from my accent
Since I am no expert at all and this configuration does not come up in any of the sites that I visited I’d appreciate any thoughts on the matter
Cheers
Helge
I live in Auckland and am really considering getting one of these systems. There are so many forums on this, ITS SOOO CONFUSING!!! Moved into a new brick place last year and the dampness is uncontrollable. I get streaming condensation, mold on the curtains and the place just feels so cold. In the summer it also gets so heavy and humid.
The one thing I have been warned from talking to a friend is DO NOT get any of the systems with built in heaters or “tempering units”. Waste of power and do very little. They had a DVS and keep the heaters constantly off.
So far I have had by far the best feedback from people on the HRV, seems like thats the quality one but guess there’s a price to match. Any knowledge of the differences between the HRV, DVS and Moisture one?
I’m going to try get some quotes soon. If you have some insights let me know and I’ll endeavor to remember to write here again when the quotes are in.
Thanks for this post Steve.
Hi Rita,
I have a moisture master and have no problem with damp and the others should be similar. The tempering is to warm up the cold air in the winter to a reasonable level rather than blow in cold air in the rooms that have not heat producing “equipment” in them. Have a word with the people in your area and see if they are using a system that works for them. In Christchurch my moisture master unit works for me.
if your wanting the best ventilation system available you want HRV ive got one and so do most people i know and work with and they all love it. moisture master is crap to be honest chinese control panel and the ducting comes off one outlet which you’ll find usually 4 or so off that one outlet, air is lazy so will go down all at different speeds of air. with HRV rest assured as your getting 2-5 air changes per hour no one else competes with that. HRV have just done a new filter upgrade so now its not just a F7 filter it has manuka extract sprayed on so will remove nasties from the home down to usually .3 of a micron a world first. HRV is nz owned and operated using a German Fan and swedish filter with kiwi build behind it, the system has two outlets at the bottom of the box for air to go through evenly and not have ducting off the main two ducting lines like the others like moisture master and DVS and Sayr. thats a small run down on HRV stick with the leader in this time because of the recession as HRV is the most stable of them all
Hi, I have an HRV which is appox 7 years. I got it for the condensation side of things and it worked amazing. But unfortunately the last couple of winters it is not working to get rid of the condensation. Its like I dont have an HRV going at all. Filter has been changed with a generic one. I paid $75 for the HRV guy to come out and found no fault. Have mailed HRV and get no response as thought it may inprove this year from last year but no. After install service not so good. It makes me wonder if they came to my house would they say the unit would work and get rid of condensation to get a sale when it does not work? Is the unit faulty even though I have had it checked? The HRV guy never said it could be the filter. Very disappointed back to wiping down windows and mould.
There was a similar problem that I heard about that was caused by a leaking pipe under the house causing an increase in moisture that HRV could not cope with. I would check all water and drainage pipes for leaks and check your roof area for moisture penetration as well.
We have a fully ducted central heating system. We have draughty wooden joinery as well. When the temperature is reached in the house, the heating system rests. It works great until the winter, we live in an area that is thick with log fire smoke outside. There is always a faint smell inside and really uncomfortable when trying to sleep. What I think happens is that when the heating system turns off, the air from outside seeps in. Still haven’t been able to figure it out.
I had Moisture Master in today and the rep suggested that by installing a heated system the house would stay ventilated and the smoke smells would be removed.
I notice that someone has mentioned the following and wonder if you can help.
“With any system that draws fresh air from the roof cavity or outside, which is then passed into the home, there could be a smell in winter, if you live in an area with lots of log fires. If you step outside your door on a winters night and you catch the sweetish aroma of smoke, that smell will probably be drawn into your home.”
Comments?
I have moisture master and if I walk outside and smell wood smoke I will probably also get a faint smell of it inside. Remember after 15 to 20 minutes the brain does not register the smell any more. We did this in an experiment at school. A horrible smell was released and ten minutes we no longer noticed it, but anyone stepping into our closed classroom did.
HRV after sales service is no good. They do pressure you into them and then give you some story about how you need two! Since getting the HRV’s installed we have had to get a heater installed in our bedroom! We also have had ice on the inside our south windows in winter. The north bedrooms of the house do not need the HRV which we were told we had to have. Wish I’d never got an HRV! They are noisy things and when you ceiling gets into the minus temps they they blow!