Whole home vent system question

Because we live in an old stone Welsh house we have suffered for years with severe condensation problems and some mould in odd corners.
I am fully aware of all the issues regards drying clothes indoors and other vapour sources.
I have therefore been researching the whole home systems such as the Lofty or Drimaster for example. BUT as I now understand the principles of how and why it works, before I buy a unit, I'm running a test by leaving two 4" vent fans running for a week as a method of air replacement.
After two days the difference has been amazing. Condensation running down the windows has almost cleared, although we still have one or two condensation points in odd corners of cold bedrooms.
QUESTION: If using two extractor fans (one shower-room, the other utility room) works so well after just two days, why can't I just use this method without spending two or three hundred pounds on a Drimaster?
Does anyone also know if I can find continuous rated and economical extractor fans to replace the current ones?
Many thanks.

 

You are extracting air which is different to how positive pressure fans work and is inefficient and potentially expensive

You seem to be extracting moist air at source, which is good, but is not the same principle as the PP fans. You are also dealing with the problem in a different way (moist air extraction, not air movement), so you really need to monitor properly whether this method is actually going to work long term. If this method is working, then it should also work if the fans were just on a humidistat rather than continuous

 

Thanks Woody.
I have seen other posts making your point, but try as I have done, I just don't understand why any one system of air replacement can be better than any other. Positive and negative systems both work on moving the moist air from the entire house. My test using extractor fans is also sucking the air out of the whole property and creating the required pressure differential, hence should suck replacement air in through all our small gaps and chimneys etc..... which it does seem to be doing at the moment.
As you say.I'll monitor carefully and see what happens after a week or so.
Thanks

 

Are the other systems you've been looking at "heat recovery" systems ?

The problem with just sucking air through the building is that you are also sucking heat out. Heat recovery systems suck air out and pass it through a heat exchanger so it can transfer it's heat to air being blown in - and so you shouldn't lose much heat at all.
So you get the fresh air & moisture reduction, but without the heating bills.

Well that's the theory, never seen or used them myself.

 

IIRC, heat recovery systems are most efficient in countries colder than the UK, so not really worth it as payback times are too long

The PP fan systems (Lofty DriMaster etc) claim to use partially warmed air from the loft, but in practice the level of loft insulation tends to mean a very cold loft nowadays and so there are complaints of the incoming air feeling cold - but siting the unit over a stairwell tends to prevent this to a large degree

PP and extract fans work in different ways and an extract fan is good for removing moist air at source or locally, but not good for ensuring that all the air in a property is moved about ... which is how the PP fans work.

So an extract fan may well remove moist air produced in bathrooms and kitchens, but if there is other moist air getting to a distant room and causing condensation and mould there, then the extract fan wont tend to deal with this

 

Im only just looking into it, but my understanding as well is that for a whole-house heat recovery system to really work well and heating costs to go down the house needs to be fairly airtight as well (google airtighness of buildings) which ofcause goes hand in hand becuase an airtight house needs ventilation.

However, with rising fuel costs rising all the time, and heat recovery technilogy cheaper all the time, to me it sounds like madness not to fit a heat recovery unit if you are going for whole-house vantilation, wihch sounds like the best solution for the OP.

We have a whole house MVHR system in my parents house (velavent sytem, fitted in the late 80's when the hosue built) and its really good. We never open windows in winter, and clothes dry overnight on the banistairs. I have retro fitted one (also a velavent) to my grandmothers bungalow for air-quality reasons, which took two of us a long weekend.

Im currentkly skint and aware im planning to move within five years, but of a family home you intented to stay in wouldnt hesitate to fit one. get one big enough for the house, fit it to the first floor, and then look at inproving airtightness and extend downstairs, as and when you have time and come re-decorate the rooms the pipes need to run through?

Dont know, not an expert, or anything do with aformentioned company, just a happy customer anda bit of a DIY/engineering type.


Daniel

 

double post

 

triple?

 

Why?

What is wrong with opening windows or natural ventilation?

Heat recovery may be a solution for a limited set of issues, but are no way a necessity or even desirable for our climate

 

Well, quite simply becuase for several months of the year (now, in febuary, for instance) its signicantly colder outside than in, which means no heat-recovered ventilation results in lost heat, and cold incoming air at the point of ventilation.

Ive not done the sums, but given the amount energy it takes to run a MVHR system I would be really very supprised if for atleast 6months of the year the energy saving is quite significant. However, that aside, having lived in houses both with and without, the reduction in condensation and removal of the need to open/close windows and tricklevents alone is in my personal experence worth the investment alone.

The kit to do my grans bungalow which would be big enough for most smallhouses (vents in two bedrooms, living room, dinning room, bathroom, kitchen and hall and two external vents) was little over a grand and as said, was fitted in a day. Larger kits are not much more and although installing on the groundfloor of a two story house would be more work its not at all impossable with a bit of thought.

Considering most people will easily spend twice that or more on a new kitchen or carpet they dont really need. I would have the venliation all day long.

Again, im not saying im right, and I am compairing an 80s house with the system, to a 40 and 50's house without, thats my personal thoughts on it.

Certainly I would (and am) consider a heat exchanged vent system for the bathroom, and run it at a reduced speed 24/7 with the door open, on full with door shut when the bathrooms in use.


Daniel

 

Heat recover systems may have certain advantages in limited situations if designed correctly and installed in airtight properties

In reality, the gains of "exchanged heat" is very little in the UK climate (not cold enough for long enough) and apart from the actual energy use and maintenance costs, you probably need some sort of airlock on all the exist doors as otherwise significant air infiltration occurs every time you go in and out

So there is no practical advantage or benefit in installing a system in a typical property - and even less so installing retrospectively in a property not specifically designed for it

 

Come on now Daniel, be honest, you've been watching last week's DIYSOS haven't you?

 

Son has a 1 year old flat with a ventilation system, uses outgoing air to warm incoming air - unit runs all the time.

Seems to work well and hasn't complained about heating bills or condensation, he has no-where to hang washing outside so must dry it indoors.

 

Never seen it, watch about 4 hours telly a week.

Im not saying it makes economical or enviromental sense, what im saying is its not an ecomonically or enviromental disaster, and in my experence it improves the conditions within the house significantly. If i do fit a system or partial system to my current house, which will be directly comparable to the house without, I will report back!

Comment about airlocks is proberbly pertainant, presumably only on external doors. Im certainly very aware that my front door currently opens directly into the hallway at the base of the stairs, in comparisen with my parents where there is a small unity room at one door and a internal porch at the other.



Daniel


Daniel

 

I started this post a few months ago by asking if I could use a couple of constant running extractor fans rather than a "whole house vent system".

I can now report back on my results for those who may be interested.........

My test period of just running two existing extractor fans was a great success, almost eradicating the horrendous damp even in the odd corners.

I therefore bought two Vent-Axia constant running 4" fans each costing only £5 a year to run! I found I could buy the two (by searching the internet) for £114 inc VAT and postage.

They've now been running almost two months and our 40 year battle with running windows and walls is over.

People will tell you that you must have a positive vent system or other types of special systems, but at least in our case, this wasn't needed.

Think about it..... If a whole house system works simply by removing the damp air by constant replacement, then ANY method of achieving this should also work.... and in our case, using two extractor fans, it is working brilliantly.

Just thought someone might be able to learn from our experience.
Although, I guess this might not work in all properties.

Cheers.