Condensation in old home

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sharlene

1 post

Wannabe Geek

#320112 7-Jul-2025 17:51

We have a 1970's home with single glazed windows and aluminium joinery. We're getting heavy condensation collecting on windows and window frames, and when its extremely cold, we see spots of condensation on the ceiling and walls too.

We've done enough renovating on the home to know that the cavities in the walls are only moderately insulated, and so is the ceiling. Happily, it's as dry as a bone inside the walls and the ceiling cavity. The concrete pad floor with underlay and carpet is also dry too.

We've been NZ homeowners for just 3 years, so this is the first time we've had to tackle this problem and we're unsure where to start. We're aware it may need to be a multi-pronged heating / ventilation / glazing solution, but where do we begin our healthy home journey? Our kiddo has asthma so we want to make an impact fast, but budget is a consideration.

Our home is fairly large and is an open plan style. We have just one heatpump in the lounge area. We'd love a ducted heating system but with a flat roof, that's out of the question.

We're concerned that adding heatpumps may increase the temperature indoors and therefore create more moisture? Is this true? We've therefore been looking into ventilation... Lossnay / smartvent fresh / smartvent tempra but is ventilation the right place to start? We're conscious the systems we're looking at will make the house even colder.

Any advise on what order we should proceed in would be greatly appreciated.

darkasdes2

428 posts

Ultimate Geek

#3391745 7-Jul-2025 18:11

I would start with the heat recovery ventilation system.

We have one in out 1960s era home and it had a moisture master system already installed when we brought the house last year.

https://www.moisturemaster.co.nz/products/heat-recovery-ventilation/moisturemaster-heat-recovery-systems

We had very little moisture in our home last winter in a 4 bedroom house.

As budgets allow, insulation, double glazing, identifying and sorting any air leaks.

Just my 2 cents worth.

Handle9

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#3391746 7-Jul-2025 18:25

Firstly:

A heat pump will not "create moisture indoors." It literally has no way to do this. It will heat or cool the air, that's all.

If you have condensation forming on walls and ceilings you have a thermal envelope problem and/or you are not heating the space sufficiently. The reason that moisture forms on a surface is that the temperature of the surface is below the dew point of the air. In Auckland today that is 4-8 degrees. If your walls or ceilings are that cold your house is too cold, you need to heat it more. Better insulation will make this more efficient.

If the wall/ceiling is warm no moisture will condensate. Windows and frames are a different story as they act as a thermal bridge to outside and it's basically impossible to stop this happening to some extent. Heavy floor to ceiling curtains will help as they will stop warm, moisture laden air contact the windows and condensate.

If you have good ceiling access get the insulation assessed, and if it's not great get a blanket overlaid. If you have recessed ceiling lights that aren't IC rated replace them with IC rated lights so you can cover them with insulation.

In parallel with this heat the space properly. This will probably sort out a lot of you kids asthma problems. Oil column heaters are cheap to buy if a bit expensive to run. Get the space warm and see what happens. Once you get the space warm you can figure out your next steps and whether it makes sense to replace electric heating with heat pumps.

A ventilation system can help with condensation but if your house is cold your house is cold. You need to get it warmer.

jonherries

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#3391754 7-Jul-2025 19:08

Handle9:

Firstly:

A heat pump will not "create moisture indoors." It literally has no way to do this. It will heat or cool the air, that's all.

If you have condensation forming on walls and ceilings you have a thermal envelope problem and/or you are not heating the space sufficiently. The reason that moisture forms on a surface is that the temperature of the surface is below the dew point of the air. In Auckland today that is 4-8 degrees. If your walls or ceilings are that cold your house is too cold, you need to heat it more. Better insulation will make this more efficient.

If the wall/ceiling is warm no moisture will condensate. Windows and frames are a different story as they act as a thermal bridge to outside and it's basically impossible to stop this happening to some extent. Heavy floor to ceiling curtains will help as they will stop warm, moisture laden air contact the windows and condensate.

If you have good ceiling access get the insulation assessed, and if it's not great get a blanket overlaid. If you have recessed ceiling lights that aren't IC rated replace them with IC rated lights so you can cover them with insulation.

In parallel with this heat the space properly. This will probably sort out a lot of you kids asthma problems. Oil column heaters are cheap to buy if a bit expensive to run. Get the space warm and see what happens. Once you get the space warm you can figure out your next steps and whether it makes sense to replace electric heating with heat pumps.

A ventilation system can help with condensation but if your house is cold your house is cold. You need to get it warmer.

Agree. This might be simpler:

Insulate the ceiling ++, heat rises, every $ you put into heating goes out the ceiling first and you can do this yourself…
Thick curtains as it is going out the windows second. The next thing if you can is seal up leaks.
Airconditioning. This is more confusing/complex, but essentially the compressor uses $1 of electricity to get $3 of heat into your house (look up thermodynamics if you want to understand how this works). It runs in reverse to cool the house in summer.
Ventilate bathrooms, make sure you have a good fan and keep it running after your shower. Make sure you have a rangehood.

Last thing that was mentioned/is key is heat you home. Comfort/international standards are 20-22 and 18 at night in bedrooms. You can get good little Xiaomi sensors from PBtech which are worth using - they do humdity and temp - you will see the humidity come down as temp goes up because warmer air can hold more moisture for the same humidity.

Jon

Stu1

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#3391759 7-Jul-2025 19:56

Insulate ceiling , can get insulation and heat pumps through rates in a lot of regions . Ducted heat pumps are over priced cheapest option is having units in each bedroom. We priced it up 3 units about 2 months ago came in at 10k. DVS or smart vent as well to help. Check you have decent ventilation in the bathroom and the kitchen . Good start

tweake

2391 posts

Uber Geek

#3391760 7-Jul-2025 20:07

+1 to what Handle9 said. tho i would add heat moves moisture. heating is a big part of keeping houses dry. one of the downsides of just heating a living room is moisture can move and settle in colder rooms. you really need to heat the whole house.

next thing is what part of the country are you in?

what sort of floor do you have (wood sheet, wood plank, concrete)? and is your house on piles (ie crawl space under the house).

all houses should have ventilation. mechanical ventilation is better than opening windows. all you need is basic positive pressure system, especially if you have typical 70's wood plank type flooring.

if you have a crawl space under the house, then you should install a ground sheet, eg poly, to stop moisture coming out of the dirt and into your house. this will make a HUGE difference.

also many of that era have breeze block walls and are problematic for moisture coming through. there is a few solutions however.

as already mentioned, temp/humidity gauges are really handy to get an idea of whats happening.

fe31nz

1229 posts

Uber Geek

#3391779 7-Jul-2025 23:45

If you stop the air circulating over the windows, only a small amount of moisture will reach the windows and be able to condense. So put up curtains over them in a way that will stop the reverse chimney effect that causes the air to circulate. The curtains need to meet the floor or window sill without any gaps at the bottom. No gaps at the side. And there should be a pelmet at the top that the curtains meet so there are no gaps at the top. As well as preventing condensation, this also stops a lot of heat loss through the windows. Still air is actually quite a good insulator. If air moves then it will move a fair bit of heat by convection.

scuwp

3885 posts

Uber Geek

#3391856 8-Jul-2025 12:50

We put in one of these. Condensation disappeared overnight.

https://www.smartvent.co.nz/

Lazy is such an ugly word, I prefer to call it selective participation

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tweake

2391 posts

Uber Geek

#3392102 8-Jul-2025 17:54

fe31nz:

If you stop the air circulating over the windows, only a small amount of moisture will reach the windows and be able to condense. So put up curtains over them in a way that will stop the reverse chimney effect that causes the air to circulate. The curtains need to meet the floor or window sill without any gaps at the bottom. No gaps at the side. And there should be a pelmet at the top that the curtains meet so there are no gaps at the top. As well as preventing condensation, this also stops a lot of heat loss through the windows. Still air is actually quite a good insulator. If air moves then it will move a fair bit of heat by convection.

actually kinda the opposite happens.

better the curtains the MORE condensation you get. by blocking the heat getting to the window, the window is colder.

this is also a trick ventilation companies pull. by putting vents in range of windows (why do you need multiple vents for the lounge? its not for airflow) so they blow air across the ceiling which will hit the wall and flow down behind the curtains. moving air past tends to keep condensation from forming. there was a really good pic of a guy in canada who tested the temp of the brass door knob on the house side of the door. its was -20c, it should have been covered in ice. but it wasn't because of the air movement from the hvac system.