2y ago

We've got an insulated house, heat it properly, ventilate it, but still see humidity levels of 70%+ in bed rooms. How to fix that?

We built a house 7 years ago and it's insulated and has double glazing. I've installed Home Assistant with temp sensors in the bed rooms and seeing 70%+ humidity levels. Temperature is always above 16c

We ventilate it, but still it's 70% in the bedrooms. WHO recommends 40-60%, so we're a bit worried.

Living room is around 55% during the day when we have the heat pump set at 21c.

As it's pretty humid outside I think it's almost impossible to get it lower, but are there any other tips? I don't want to run dehumidifiers. Would an HRV like system help?

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So your house is insulated and warm, and presumably pretty sealed. I think you should be considering sources of water vapour.
Some common sources:
Shower
Drying clothes inside
Cooking
If you have a separate shower (rather than shower over bath) you can get a shower dome which significantly reduces steam leaking outside the shower. I don't much like using a shower with one but they are effective. You can also get a more powerful extractor fan, though even the super powerful ones don't seem to be that powerful (I want one that sucks your clothes off).
If you dry clothes inside, try not to. If you have a dryer that isn't a condenser dryer, try to vent it outside or at least open the window. Probably try to use it less though using it less and not drying clothes inside don't make for many options in the winter.
For cooking, make sure you have a rangehood to catch the steam from any boiling pots. And make sure it's externally vented. I have lived in placed with rangehoods that just push the air back into the room (I'm not sure of the point...) but I'd think with a house that new it wouldn't be an issue.
You might have other ideas about sources of water. Gas heaters can be one but it sounds like you heat with a heat pump.
An HRV/DVS can help but I'm not sure it's as effective in a newer house.
You also mention the living room is 55% in the day when heated to 21c, what temperature are the bedrooms when they are 70%? Colder air can hold less water, and so the relative humidity is higher with the same amount of water in the air.
- Thanks Dave, much appreciated! Yes, I guess it's from internal sources, like shower, drying clothes and cooking. Will try to decrease that, but as you said, drying clothes outside is not really an option in winter.
  So, right now, living room is 21.5C@57.1%. Bed room 1 is 18.1c@67.6, bed room 2 is 17.8@70.4%, bed room 3 is 19.1c@65.3% We've got doors open so it should stabilize a bit more. I understand that higher temps means lower RH, but I don't want to heat bed rooms to 21c. There are panel heaters in each bed room, which are set at 16c during the night, and at 19c at the end of afternoon until 6pm.
  Garage is 14.6c@77.7; which is not insulated & not heated.
  Think as a gap stop I'll get a dehumidifier, especially for the colder winter months.
  
  Other than the garage, those temperatures/humidities all have a similar amount of moisture in the air, the difference comes from the temperature of the room. See this calculator I googled up: https://www.omnicalculator.com/physics/absolute-humidity
  So the warm air has X amount of water in it, and when it goes to the cold room it still has the same amount of water, but because cold air can hold less water the relative humidity goes up. So I don't think there's anything special about the bedrooms.
  The dehumidifier is probably a good idea, but before you go and buy one, check if your heat pump has a "dry" setting.
  
  You could probably solve most of this problem by installing an ERV but those are fairly expensive.
What do you mean exactly you ventilating. Mechanical ventilation?
Modern houses NEED mechanical ventilation. It's a travesty that new houses in NZ don't come with mechanical ventilation as standard, as is done in the rest of the developed world.
It's pretty obvious if you think about it. Seal the house well, well insulated, double glazed. How will the moisture leave without ventilation. This is why modern houses NEED mechanical ventilation. Older houses don't need mechanical ventilation because the house is already leaky.
And not the silly DVS thing. I don't want rat infested air from my attic thank you. I don't care how good the filters are. Ventilation from the outside please.
What this looks like is intake vents in the soffit, a duct, and fan that pumps fresh air in for positive ventilation. Our you can do negative pressure where it pumps out, or balanced where you have air coming both in and out. You can install a mechanical heat recovery system if the house gets cold.
Full HVAC includes ducted heating/cooling.
TLDR: your house is humid because it's well sealed and the builders couldn't be bothered putting in mechanical ventilation because we are 20 years behind the rest of the world.
If you already have mechanical ventilation then it is likely not installed properly. Just putting it in doesn't necessarily mean it's sized correctly for example.
- What do you mean exactly you ventilating. Mechanical ventilation?
  We've got mechanical ventilation in the bathrooms.
  But I meant just old school opening all the windows :)
  TLDR: your house is humid because it’s well sealed and the builders couldn’t be bothered putting in mechanical ventilation because we are 20 years behind the rest of the world.
  Yes, I understand that, we generate moist from cooking/breathing/washing and that has to go somewhere. We've got many windows open a little bit 24/7.
  I'm from Europe, and yes, houses are better insulated, we had double glazing 30 years ago, and now have triple glazing, but ventilation was never an issue. We just open our windows to ventilate for e.g. an hour and that's it.
  
  4 year old house, double glazing. We have the heat pump set at 21dg on 24x7 all winter and never really open windows.
  Current temps and moisture levels:
  If you're worried about moisture I recommend a dehumidifier, those things work wonders and much cheaper than retrofitting ventilation like the other poster mentioned.
  I guess it's worth mentioning, we have a tumble drier in the garage so the house doesn't get any moisture from drying clothes.
  
  Thanks for further details. I would definitely invest in getting HVAC installed in that instance or if cost is an issue then at minimum install simple positive pressure mechanical ventilation from the outside into the bedrooms. This should fix your problem. It sounds like windows aren't enough because the house is well sealed, so you need a mechanical solution. Please don't get DVS from the attic.
  I live in a new house with HVAC and leave the mechanical ventilation on when not heating or cooling and it keeps moisture levels low. I also got HVAC retrofitted into my previous house which made a massive difference in moisture. I'll never live in a house without HVAC in the future if I can help it.
  
  You would probably have had air bricks too.
70% you need to be running dehumidifiers...
It's not just mold that's an issue, it can cause structural damage.
- As I understand it, dehumidifiers are not a proper long term solution for an entire house; they are recommended for rooms where ventilation is hard.
  
  You can call an HVAC specialist and get something more permanent, but you need to do something ASAP.
  But you can absolutely get one with a drainage tube and run it 24/7 tho. Lots of people in older houses in America do it.
Vapour barrier. Vapour barrier. And maybe a vapour barrier.
They're really cheap and only a little difficult to install. I've installed them in every house I've ever lived in. In our current house things dried out so much some of our floorboards warped a little. They are magic.
- Never heard of that, thanks. Our house is built on a concrete slab, so don't think that will work?
  
  If there's an air-gap between the slab and your floor, and you can get in there, then yeah it will help. Concrete is remarkably porous to water.
  
  Sounds like a reasonably new build. If it’s slab on grade they would have put down a vapour barrier prior to pouring the concrete slab.
Hvac is oversized and not running long enough. Super common issue especially when people tighten up their house
What sensors are you using to measure your humidity? Have you got anything you can calibrate against?
- I've got Sonoff SNZB-02 temp sensors. I also have a weather station; there is a difference of up to 5%, so I am taking the readings with a grain of salt.
  I just bought a dehumidifier which has a RH sensor as well, which is almost the same as the reading of my Sonoff sensors.

102 comments