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#272835 19-Jul-2020 10:13
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We have a new-build 4-bed home in N Canterbury, 235m2 with 3x heat pumps. It is warm and comfortable as you'd expect but in the coldest winter months we do get quite a bit of condensation on our bedroom windows which are the typical double-glazed, aluminium framed ones most new builds have. There is usually somebody at home all day so we in winter we usually have 2 of the heat pumps running 5am thru to around 9pm and off in-between.

 

We have had a quote for a DVS system (not the heat recovery system, but the system with a fan in the roof blowing air into the home) but after doing a bit of research and reading through some of the threads about those systems on this website I just don't know if it's the right thing to do. I'd be really keen to hear from anybody who has a similar setup - i.e. DVS or similar in a new-build home. Does it eliminate condensation for you? Does it make the house any colder?

 

The heat pumps do have a 'dry' mode - would it achieve the same thing if we simply left the heat pumps on dry mode at night instead of turning them off? Would that cost significantly more in power than running a DVS system?

 

 


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896 posts

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  #2525574 19-Jul-2020 12:10
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Every time I've installed one of these types of systems I've had positive feedback that it's got rid of the condensation problem. The idea is the fan is running full time and moving air from either outside or inside the roof. I am a bit surprised you are getting a lot of condensation inside a home that is so new but maybe this is common in colder areas? 

 

Dry mode on heat pumps will do what a dehumidifer does, so as long as it reaches those rooms it should work

 

Edit: I should add that while I have not had issues with my installs, I do remember HRV being on fair go and saying their systems just wont work in some houses...what houses they are I do not know. Mine have been brick and tile or weatherboard/iron/tile


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  #2525586 19-Jul-2020 13:15
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Ventilation without heat exchanger has the same effect as open window. I have one of these and its brilliant for the purpose of fighting condensation. However, it moves cold air inside the house. Not much of the problem in Auckland, but does get cold for a week or so during the year. The most simple system costed me 1400 for 3 outlets. Does the job. I'm happy. Most expensive is labour. If you can do yourself if there's power at attic - can be installed for 200-400 at most incl multi speed 12v fan and smart socket :) does the job.




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  #2525591 19-Jul-2020 13:31
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Most positive pressure ventilation systems (e.g. DVS) force in dry (sometimes cold) air into the house and rely on the house being "leaky" enough to let the moisture laden air out through cracks and gaps around doors and windows etc.

 

 

 

The problem with newer airtight double glazed homes is that they tend to be warmer and can therefore hold more moisture in the air, and a PPV can't force it out, unless you have some form of vent or even open windows.

 

 

 

I think the best solution would be for a heat recovery system, with returns in bedrooms etc. this would allow the moisture laden air out, and temper the incoming cold air.


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  #2525624 19-Jul-2020 15:01
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look at ways of getting rid of the moisture in your house. as that's why the windows are condensating. consider running the heat pumps in the dehumidify mode for a few hours a day, consider opening windows to let out the warm moist air. unless you air the house you are not getting rid of the moist air.

 

This would have been better addressed during the build then now.


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  #2525627 19-Jul-2020 15:06
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How does opening windows help when outside air is 100% humidity, I've always wondered this.





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  #2525628 19-Jul-2020 15:07
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Spyware:

 

How does opening windows help when outside air is 100% humidity, I've always wondered this.

 

 

is it though?


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  #2525635 19-Jul-2020 15:13
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It is. Christchurch, inside 46% humidity, outside 99% humidity. Still get condensation on windows simply because they are cold. Best is to run heat pumps 24/7. Night is coldest so a super idea anyway, can be as low as -5 outside, 20 degrees inside.





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  #2525778 19-Jul-2020 18:07
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Humidity is related to temperature.

 

Just because the cold air outside has a high humidity, doesn't mean it will have the same high humidity when brought inside and heated to room temperature.

 

Outside air with 99% humidity at 5Celcius will have a humidity of 39% when heated inside to 20Celcius.


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  #2525825 19-Jul-2020 20:10
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There are a whole heap of threads on here that explain the merits (or lack of) the DVS/HRV systems, have a google of "Geekzone: HRV"

 

Try the dehumidify mode on your heat pumps otherwise look at getting a ventilation system with heat exchange that vents outside and grabs fresh air - not into your ceiling.


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  #2525832 19-Jul-2020 21:02
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I think dry cycles on a heat pump use a bunch of power. They basically run in "cool" mode to dehumidify then "heat" mode to stop the room getting really cold. I suspect it will cost a bit to use it, and on the rare occasion I use them I don't find them very effective. I don't need them often though, just say when the carpets are cleaned.

 

Where is the moisture in the house coming from? Do you have good strong exhaust in the bathroom and over the stove? That's a key thing to do. Is any dampness coming in from under the house? Removing the source of water is key, unless it's people breathing and such, which you can't avoid.

 

I wouldn't put a standard positive pressure system into a nice new house. You could, and you could run it a few hours a day on a basic timer (Kasa Wifi or standard Mitre Ten) and it will probably reduce the problems, but it makes the house colder and / or increases your power bill. You'd want outlets in each bedroom if you can, and in common areas. As it's been said, you might need windows open to give the air somewhere to go. It would help, even run 4 hours a day, as that reduces the moisture in the house a lot by putting in cold air. I prefer to bring in fresh air from outside rather than ceiling cavity air, which is lower quality air. I put external air through a HEPA and active charcoal filter to remove dust, pollen, and smells, filter works great.

 

I would probably go with heat recovery ventilation (the concept not the brand) in a new house, so you're not just throwing heat away. Yes it can cost more, but it will be more comfortable and pay for itself. Look at Cleanaire, that's who I liked when I was looking, but I didn't do anything about it yet. I would still run it on a timer so it's not blowing all the time, you don't need it running constantly. If you get one run it 24/7 for a week, then I'd run it a few hours during the day, maybe a couple of hours in the evening, see if that's enough. A good filter as I mentioned above can help, only cost me $120 for a filter that does both.


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  #2525844 19-Jul-2020 22:19
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You could probably run a positive pressure ventilation system. I ran one in my previous house, worked well. It was a lot smaller though, so our condensation was quite bad in our master bedroom (pre installing the ventilation system).

 

I put a ducted heatpump in my next build of similar size to yours and condensation is so minimal I don't even worry about it. My theory is that all of the air in the house is mixed together during the day so overall moisture levels are stread around the house. Rather than being concentrated in master bedroom / ensuite.

 

The system I had in old place had a single vent in hallway and reduced our condensation by 99%. I ran it 24/7 so needed to heat the house more, but as mentioned above, you could set it on a timer. Even running all of your heatpumps 24/7 won't solve the problem. 

 

Where is the moisture coming from? Long hot showers with limited use of extractor fan in ensuite? Fan could be s**t? Is it only in your bedroom or every bedroom that people sleep in?

 

 


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  #2526764 21-Jul-2020 20:46
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Froglotion:

 

Where is the moisture coming from? Long hot showers with limited use of extractor fan in ensuite? Fan could be s**t? Is it only in your bedroom or every bedroom that people sleep in?

 

 

 

 

Non-thermally broken windows from the sound of it ie moisture content doesn’t have to be abnormally high.


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  #2526827 21-Jul-2020 22:59
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What about a reasonably priced balanced pressure unit with heat exchanger?

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  #2526852 22-Jul-2020 07:48
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We went from a 1920s bungalow to a brand new build in Rolleston earlier this year and were surprised by the amount of condensation, our windows were soaked each morning, we must be hot sleepers and we weren't opening the windows on really cold mornings. At the recommendation of some of the people here on GZ and doing lots of research we ended up going with a Cleanaire balanced heat recovery system and it's been brilliant, it's completely sorted the condensation problem. The house is 235m2 and the system was $6.5K installed.


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  #2526986 22-Jul-2020 11:17
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old houses leak air which helps with humidity levels and condensation, newer houses are more airtight and unless you ventilate them you will get humidity


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