Direct Air vs Air from Room - for Wood stove. What's best for high humidity house?

[CornishWoodworker]

Hi all

A bit of background: I live in the Brecon Beacons surrounded by a lot of trees and a stream, all of which I presume lends to the high relative humidity (RH) in my house. It often sits in the 70% region and sometimes even creeps above 80%. In times of high RH, opening the window is counter productive and causes it to rise. We use a dehumidifier when it's at its worse.

We have a wood burner in one room, which does not have a direct (external) air feed. It's not been in long, but it does do a good job of reducing the RH. We'll soon be installing a further two wood stoves. I totally see the sense in direct air in as much as it will minimise drafts, and negate the need for a vent which would let copious amounts of cold air into the house...

But when it comes to humidity I can't get my head around it. No direct air to the stove means more air changes and air circulation in the house (I think?), which could be looked upon as a good thing. But then again, it also means more air coming from outside, where the humidity is higher, so perhaps it isn't such a good thing. And maybe that's all too basic a way too look at it anyhow.

I wondered if anyone out there has a better understanding of the science behind this and could explain which option is best and why, when it comes to humidity?

Many thanks

Use a stove with a balanced flue.
Air drawn in may be moisture rich but that direct into stove and then expelled.
Result
Warm house with reduced interior humidity

https://www.islandpelletstoves.co.uk/balanced-flue-for-wood-stoves/

 

[MikeJhn]

The use of a mechanically ventilated heat exchanger (called a VMC/CMV in France) will suck out humid hot air separate the moisture from the air as condensate and return the air moisture free to the rooms heated from the secondary plenum in the unit, have a look here: https://www.leroymerlin.fr/produits...tilation-mecanique-controlee/vmc-double-flux/

Or here: Mechanical Heat Recovery Ventilation | MVHR | EnviroVent

 

[Jacob]

So do you! A guy i knew fitted a pot bellied stove to a small yacht he lived on, one winter the Medway patrol boat noticed his boat anchored for some days in a remote place with snow on the deck, they had a look & found him dead in his bunk, It was found that he had shut all the hatches & had died of carbon monoxide poisoning.
When we fitted our stove building regs said we must have two vents (air intakes) from underfloor near the stove. They are usually shut as they cause bad drafts but if the stove is going i open them & the cold air goes into the stove alcove & gets hot pretty quick!

Similar with caravans and even tents. Small spaces, well sealed, unventilated and smouldering fires, or gas appliances etc - calor gas lantern in small tent can be bad news

 

[Stevekane]

I often wondered how people get on with those highly insulated homes you somtimes read about, so super insulated that just the people and a light bulb will keep them warm,,what happen to all the moisture created by the occupants and cooking etc,,I suppose they have the fancy heat exchangers fitted? Actually thinking about it they cannot be getting much heat from a modern light bulb anymore either! Its the future though and I wish we could have a bit more insulation on our old and cold house. Were still holding off lighting the stove, have a good pile of wood ready to go and we had one evening with the central heating on just to make sure the 40plus yrs old Potterton Kingfisher was still running okay,,,which thankfully it is,,I keep thinking about changeing it but the new boilers, stuffed full of cheap chinese electronics worry me too much.
Steve

 

[Jacob]

I often wondered how people get on with those highly insulated homes you somtimes read about, so super insulated that just the people and a light bulb will keep them warm,,what happen to all the moisture created by the occupants and cooking etc,,I suppose they have the fancy heat exchangers fitted? Actually thinking about it they cannot be getting much heat from a modern light bulb anymore either! Its the future though and I wish we could have a bit more insulation on our old and cold house. Were still holding off lighting the stove, have a good pile of wood ready to go and we had one evening with the central heating on just to make sure the 40plus yrs old Potterton Kingfisher was still running okay,,,which thankfully it is,,I keep thinking about changeing it but the new boilers, stuffed full of cheap chinese electronics worry me too much.
Steve

Spot on. Some improved technologies just create new problems as they over-ride old solutions. Having a draughty window is a good way to ensure adequate air exchange rates and reduce condensation. Opening it increases the rate.
Apparently Florence Nightingale recognised the need for fresh air and highly recommended sash windows as they are so good at controlling ventilation

 

[StephenArfer]

Whatever type of combustion device in use, I would strongly suggest installing a good quality Carbon Monoxide detector alarm. I use "FireAngel" CO detectors with a 7-year sealed battery life. As it happens I have also used them along with FireAngel fire detectors in the house for the last few years. No failures or false alarms. They are sensitive and will warn long before CO concentration reaches an unsafe level. Best not to be around spinning blades etc. when you start to feel dopey.

 

[Jameshow]

The use of a mechanically ventilated heat exchanger (called a VMC/CMV in France) will suck out humid hot air separate the moisture from the air as condensate and return the air moisture free to the rooms heated from the secondary plenum in the unit, have a look here: https://www.leroymerlin.fr/produits...tilation-mecanique-controlee/vmc-double-flux/

Or here: Mechanical Heat Recovery Ventilation | MVHR | EnviroVent

Could you not make a laberinth heat exchanger which extracted heat from stale air and warmed incoming warm air?? Two sheets of plywood with an Alu maze to promote the transfer of heat?

Cheers James

 

[hairy]

Our house has about 400mm of insulation all around, a 5KW Morso Squirrel and window trickle vents with a CO monitor. Yesterday with a bit of sunshine we had 21degC in the main room. Most visitors struggle when they come round complaining it's too warm, but the fire hardly gets lit until it's either properly cold out or the wind comes from the east and we've left the trickle vents open. I've never had a house this insulated and I still can't believe how well it works.
Currently 12degC outside and 95% humidity, 20C and 67% inside, we had a fire on Saturday for a few hours and no heating since. I love it.

 

[Krome10]

Fantastic responses - thank you all very much! A bit tied up right now, but will respond more fully soon. Until then, thanks again