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Humidity, or lack thereof... is my heat pump making rooms drier?

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Air Source Heat Pumps (ASHPs)

Last Post by AndrewJ 2 months ago

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AndrewJ

(@andrewj)

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Topic starter 19/02/2026 10:05 pm [#2839]

The humidity in my house is very low since the heat pump started providing heating - most rooms are somewhere between 30% and 40%. Bathroom is higher after a shower obviously and some of hat persists during the day but is down around 45% by the end of the day.

Is this something that is common? What do you do?

This topic was modified 3 months ago by Mars

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Deltona

(@deltona)

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19/02/2026 10:16 pm

What makes you think it's too low?

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trebor12345

(@trebor12345)

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19/02/2026 10:25 pm

Posted by: @andrewj

↑

The humidity in my house is very low since the heat pump started providing heating - most rooms are somewhere between 30% and 40%. Bathroom is higher after a shower obviously and some of hat persists during the day but is down around 45% by the end of the day.

Is this something that is common? What do you do?

I am currently at 37% RH and it's been at that level for most of the winter season. I believe it comes from the underfloor heating being on 24/7.

My previous houses would have been some 60/70%.

Hitachi Yutaki SCombi Heat Pump
(Indoor Unit ) RWD-3.0RW1E-220S-K
(Outdoor Unit) RAS-3WHVRP1

2024 build bungalow, Southern england, 179 m2, 14w/m2
Underfloor heating all fully open
7KW heat pump
50 litre buffer tank (4 port)
3.6KW solar panels

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AndrewJ

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Topic starter 19/02/2026 10:44 pm

@deltona I always thought a range of 40% to 50% was a good level to have. It can feel a little dry sometimes and I wonder if it’s good for wooden furniture.

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Majordennisbloodnok

(@majordennisbloodnok)

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20/02/2026 12:36 am

Posted by: @andrewj

↑

@deltona I always thought a range of 40% to 50% was a good level to have. It can feel a little dry sometimes and I wonder if it’s good for wooden furniture.

Actually, it’s better for wooden furniture – or at least the consistency is. It’s the swings in humidity that cause the problems unless the furniture is well designed.

As for people, guidelines vary; 30-50%, 40-60% and the NHS’s own 50-55%, so the 30-40% you mention is on the low side but definitely better than being too high. @andrewj, how many house plants have you? They’re a well proven way to gently raise humidity; 5-6 medium ones can raise it by 10-15%.

This post was modified 3 months ago by Majordennisbloodnok

105 m2 bungalow in South East England
Mitsubishi Ecodan 8.5 kW air source heat pump
18 x 360W solar panels
1 x 6 kW GroWatt battery and SPH5000 inverter
1 x Myenergi Zappi
1 x VW ID3
Raised beds for home-grown veg and chickens for eggs

"Semper in excretia; sumus solum profundum variat"

👍

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Deltona

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20/02/2026 7:48 am

Posted by: @andrewj

↑

@deltona I always thought a range of 40% to 50% was a good level to have. It can feel a little dry sometimes and I wonder if it’s good for wooden furniture.

I'd be happy with what you have (so would millions of others), if you aren't actually 100% seeing any ill effects then conclude that it's fine.

👍

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AndrewJ

(@andrewj)

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Topic starter 20/02/2026 10:54 am

@majordennisbloodnok really? We have loads, but they are all in the conservatory. Maybe I need to distribute them a bit more.

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AndrewJ

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Topic starter 20/02/2026 10:57 am

@deltona It feels a bit dry and definitely a result of this heating. I never measured it with the gas CH but it was more comfortable and condensation was never a problem.

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Majordennisbloodnok

(@majordennisbloodnok)

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20/02/2026 11:09 am

Posted by: @andrewj

↑

@majordennisbloodnok really? We have loads, but they are all in the conservatory. Maybe I need to distribute them a bit more.

That would make sense. I've found the effects are pretty localised so spreading them around is a good idea.

Obviously, a humidifier will work well but I generally feel that if I can avoid unnecessary electrical consumption then that's a good thing. Plants naturally deal with humidity and make a home feel more "homely" (in my opinion) so are a good leccy-free alternative.

Transpiration is the natural plant process that increases humidity in that water absorbed through the roots will end up evaporating from the leaves. Plants with bigger leaves or more leaves will have a greater effect, for obvious reasons. Conversely, many plants are also able to absorb moisture from the surrounding air and so reduce high humidity, and since quite a few of the best known plants for one problem are actually pretty good at dealing with the other problem too, you may be able to mitigate against both extremes at the same time.

Some classic recommendations:

Boston Fern
Peace Lily (for very different and personal reasons, my favourite)
Areca Palm
Spider Plant
Rubber Plant
Philodendron
Bamboo Palm

"Semper in excretia; sumus solum profundum variat"

🧐

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IRMartini

(@irmartini)

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20/02/2026 1:40 pm

I've found that generally the humidity in the house is lower in the winter and higher in the summer.

I assumed this was due to cooler air being dryer or unable to 'contain' (is that the right word?) as much moisture as warm air rather than anything to do with heating!?

“Anything worth doing, is worth doing right.”

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Mars

(@editor)

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Joined: 5 years ago

Posts: 4549

20/02/2026 3:16 pm

I remember reading about this a couple of years ago, so I hope I remember it correctly (andn the numbers are roughly accurate), but when you warm air up, its ability to hold moisture increases. So even if the actual amount of water vapour in the air stays the same, the relative humidity drops. That’s why homes often sit at 30-40% in winter once the heating is running steadily, whether it’s a heat pump, gas boiler or anything else.

In fact, heat pumps can sometimes feel drier simply because they provide more continuous, even heat rather than short hot bursts.

Below 30% is where people tend to notice dry skin, sore throats, static, etc. Bathrooms spiking after showers and then drifting back down is completely normal too.

Love the info about indoor plants @majordennisbloodnok... we have loads. That's very interesting indeed.

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Mars

(@editor)

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20/02/2026 3:35 pm

@majordennisbloodnokjordennisbloodnok, this is in an intriguing direction you've taken this discussion in.

If you can nudge humidity back into a comfortable range without plugging something in, that’s awesome. Plants are also a far more elegant solution than having a plastic box.

As you say, transpiration does the work in the background, and the effect is nicely self-regulating. There’s also something psychologically important about greenery in winter. When heating systems run steadily, homes can feel a bit “sealed” and clinical. Plants soften that.

Our indoor plants on the hallway featuring a spider plant.