Indoor humidity

its all relative.

our house sits at 17degc most days and is 70% humidity. W<span style="font-size: 12.8px;">e have condensation issues.</span>

increase that temp and the humidity drops.

Humidity is difficult to quantify(wrong word) as it's temp dependant so a % at one temp drops as the temp rises although the amount of moisture doesn't change.

That said my weather station thing puts a smiley face icon on at around 60-65% at 16°C.

Living room currently 16.7 degrees, humidity is 76%. No idea if good, bad or indifferent, but I'm not cold, only 'windows' are the patio doors and no condensation. Outside temp currently 9 degrees ish.

40-50% is out target. after a couple of years of inadvertently growing mold in our house in the winter and associated respiratory issues

It’s inescapable at the moment. It’s mild out (daytime 15c here in the SE) and 80-90% RH outside. The house is comfortably a few degrees warmer without even having the heating on thanks to solar gain, so there’s nothing to really reduce the humidity. If it were 10c 90%RH outside and the heating were on, then by the time we heat that air the relative humidity would be more like 60% or less.

Relative humidity is… relative. It’s a measure of how much water the air can hold before saturating/condensing. Warm air can hold more. Dramatically more. So if you bring in cold air at 90%RH, then heat it, it becomes warm air at 50%RH, for example.

Present conditions are not really a condensation concern. It may be 80% inside but there will be little condensation and mould. Once the weathers cold enough to cause serious condensation risk on walls and windows then humidity should automatically come down with the heating but let a bit of that cold dry air in if it’s not coming down. Any black mould spots use a mild bleach to wash down.

@bearback that chart makes sense but only for proper winter when temperatures are lower. You wouldn’t consider, for example, 90% humidity to cause allergic rhinitis if it’s 35c outside. But you would if it’s 90% RH in your house and it’s 0c outside. That’s because parts of your house, eg exterior walls, will be at 10c and condensation will be happening there and bacteria will be growing.

Right now we’re in between winter and summer conditions (even though it should really be winter already) and so indoor humidity will be high but condensation risk will be low.

If you have specific health concerns continue to use ventilation as you would in summer because it’s warm enough heat loss should be low. Balance this with your heating budget. As conditions really start to cool indoor RH should lower.

Good info goldfish, thanks. Thing to remember over Winter is continuing to ventilate it seems. Whilst the idea of opening windows when it's cold outside doesn't appeal, a 5-10 min burst should replace the stale air inside and help avoid any condensation issues. Doing this whilst having the heating on more sounds like it should lower the humidity levels from what they are staying at (65-70%), but time and an unhealthy attention to the hygrometers around the house will tell.

Jolsa
Full Member

Good info goldfish, thanks. Thing to remember over Winter is continuing to ventilate it seems. Whilst the idea of opening windows when it’s cold outside doesn’t appeal, a 5-10 min burst should replace the stale air inside and help avoid any condensation issues. Doing this whilst having the heating on more sounds like it should lower the humidity levels from what they are staying at (65-70%), but time and an unhealthy attention to the hygrometers around the house will tell.

The problem for me is, it's been so wet that this hasn't been working for the last 2-3 weeks. I know wet outside air should be lower rel humidity when warmed but the house refuses to budge below 75% with this method.

When it is as wet out as it has been (combined with being warm) the house will always be high. The lowest I have seen it (Under 40) without use of dehumidifiers is on cold but very dry spells in winter.

Whilst the idea of opening windows when it’s cold outside doesn’t appeal, a 5-10 min burst should replace the stale air inside and help avoid any condensation issues.

That is the best strategy indeed. Well it’s what I do anyway, I’ve heard it described as the German model. I get excited when there’s a cold clear dry morning because that air has so little moisture. Throw open all the windows. And doors even. Five or ten mins. The fabric of the house will still be warm but the air you’ve swapped in will be dry, it will warm up quickly. A little dose of heating on if you can and you’ll be back to a comfortable house with lower humidity.

But as I tried to explain yesterday, don’t worry about high humidity too much in the current weather conditions.

Lüftung!

Germans love it.... GF's folks constantly opening the windows, although that might only be whilst I'm there and farting. God knows what their heating bill is going to be this year.

Mine's hovering around 60-65%.

Thing to remember over Winter is continuing to ventilate it seems. Whilst the idea of opening windows when it’s cold outside doesn’t appeal, a 5-10 min burst should replace the stale air inside and help avoid any condensation issues.

Recently purchased an Aranet4 monitor and it has highlighted just how bad I was at this. The CO2 level in the bedroom by morning and in the room I work in during the day were in the 2k-5k ppm range which is described as "Headaches, sleepiness and stagnant, stale, stuffy air. Poor concentration, loss of attention, increased heart rate and slight nausea may also be present". 10 mins of windows open both ends seems to replace all the air. It was up to 4k by morning in the bedroom, still up to 3k with the vents at the top of the window open.

I have a very poorly balanced MVHR system, humidity is around 63% in the hallway according to my Nest thermostat, a little higher in the bedrooms if the cheap humidity sensor is correct. It will rise in our bedroom overnight as the inbound air feed is slowed right down in the middle of the night. So we get continuous air exchanges and the humidity is still in the 60s. We aren't blasting the heating on too high either. It'll get to 19 tops in the hallway (we set it to 19 that is) if we put it on, normal temp is around 18/18.5 in the hallway. It dropped to 17 today after a few days of it being off, but it was much colder last night than it has been for some time. Utility room ceiling (currently don't have one) is still open to the cold roof so once that is finished I hope the house can keep a temp for a little longer.