Mechanical Ventilation

Worldlywanderer

I am currently renovating my Victorian home and have discovered in a number of areas that decisions are needed which are usually made by tradesmen based on their knowledge of regulations and regularly ignore science. For example, I am currently considering ventilation. When considering why I might require ventilation I ignored the regulations and used common sense. the answers I came up with were simple; I like to be comfortable and healthy.

Cutting to the chase it became apparent that I needed to avoid mould growth, control humidity and remove odours. The answer I came up with was to use a humidistat to turn on an extract fan at a given level of humidity. Positioning fans in the areas where moisture is most likely to be concentrated seemed sensible so I decided to talk to the experts. That’s when I discovered that the experts (technical department of extract fan manufacturer) are only concerned with selling whichever model of their fan meets regulations in a given situation.

My research suggests to me that mould starts to grow at around 55% humidity so I should look to extract damp air above that level but fans generally work on two settings 60% and 90% - is there a scientific reason for this and at what level of humidity should I set my fan to operate? Then I discovered that humidistats operate on ambient humidity. The ambient humidity where I live is 69% today and averages 80% in April. I am now reconsidering why, fundamentally, I want to drive a four inch hole through my wall at all or whether I should simply rely on opening a window.

Experts talk about air flow in litres per second and how many air changes are required per hour. Taken together this suggests it is possible to calculate which is the best fan for a particular room but regulations get in the way and fan manufacturers say that the size of the room is irrelevant - maybe to regulations but surely not to achieving a healthy environment. Do I need a fan with a greater capacity for a larger room and if not, why not?

footyguy

Worldlywanderer wrote: »

I am currently renovating my Victorian home and have discovered in a number of areas that decisions are needed which are usually made by tradesmen based on their knowledge of regulations and regularly ignore science. For example, I am currently considering ventilation. When considering why I might require ventilation I ignored the regulations and used common sense. the answers I came up with were simple; I like to be comfortable and healthy.

Cutting to the chase it became apparent that I needed to avoid mould growth, control humidity and remove odours. The answer I came up with was to use a humidistat to turn on an extract fan at a given level of humidity. Positioning fans in the areas where moisture is most likely to be concentrated seemed sensible so I decided to talk to the experts. That’s when I discovered that the experts (technical department of extract fan manufacturer) are only concerned with selling whichever model of their fan meets regulations in a given situation.

My research suggests to me that mould starts to grow at around 55% humidity so I should look to extract damp air above that level but fans generally work on two settings 60% and 90% - is there a scientific reason for this and at what level of humidity should I set my fan to operate? Then I discovered that humidistats operate on ambient humidity. The ambient humidity where I live is 69% today and averages 80% in April. I am now reconsidering why, fundamentally, I want to drive a four inch hole through my wall at all or whether I should simply rely on opening a window.

Experts talk about air flow in litres per second and how many air changes are required per hour. Taken together this suggests it is possible to calculate which is the best fan for a particular room but regulations get in the way and fan manufacturers say that the size of the room is irrelevant - maybe to regulations but surely not to achieving a healthy environment. Do I need a fan with a greater capacity for a larger room and if not, why not?

I'm no expert, but extraction fans are usually installed only in areas that produce high levels of humidity (steam) e.g. in kitchens & bathrooms.

The problem with extraction fans (or opening a window) it that it not only expels humid air, but also warmth.

What's more, if the ambient humidity is generally between 69% and 80%, I can't see how either a fan or opening a window will reduce the humidity indoors to well below that (55%)

Have you considered using a demuidifier instead?

Richie-from-the-Boro

Humans cause humidity, fancy expert gizmo's are no better than a cheap dew meter, kitchen bathrooms and gas fires contribute almost all of the rise in the UK average which ordinary ventilation takes care of after April is over. Are you in the UK ?

Pincher

I put in some air ducts during a major renovation, in anticipation of needing to put in a MVHR (Mechanical Ventilation with Heat Recovery) air exchange unit.


Despite having no trickle vents on the 30 year old double glazing, and draught strips on external doors, enough air seep through the floorboard/skirting to remove the moisture content, plus I open the windows from time to time.


I also have PIR/Humidity sensor bathroom fans, which also help.


Basically, there is no need for a MVHR unit at all.


I consider it rather precarious to actually have a house so air tight that that you depend on having a MVHR working all the time. What if the MVHR fails? I prefer to have a house that naturally breathes, even if it's not ultra heat efficient.