Bathroom extractor fan or DMEV

[atomsvoyage]

My house was built in 1981 and for some reason doesn't have any ventilation in the two upstairs bathrooms, other than windows which can be opened. I want to fit some ventilation system to reduce condensation and moisture build-up as we do get some mould appearing on the ceiling and around the windowframe. Looking into the various systems I can't work out whether to get some inline fans in the loft and out through the eaves vent, or put in a continuous DMEV system in each room. As far as I can tell, the extractor fans will be noiser when in operation, but could be fitted directly above the shower and pull out all the moisture very efficiently. What's the advantage of a DMEV system and which should I be thinking about? Looking to stay in this house for the next 10-15 years.

[JohnMo]

dMEV.

Almost silent in normal mode, quiet in boost mode. Low and slow continuous ventilation.

 

You need a window vents be open in dry room (bedrooms etc) to be effective as they use cross ventilation to sweep out CO2 in bedrooms and damp air in wet rooms.

 

But more expensive than a normal extractor.

 

Normal fan, makes a racket only on for a short time, not really sure how effective they are if you have a damp issue.  Cheaper than dMEV.

 

What ever you choose, don't position near a window or doorway, as it will not be effective.

[atomsvoyage]

Thanks JohnMo, that's helpful. What's the issue with positioning near window or doorway?

[Iceverge]

12 minutes ago, atomsvoyage said:

What's the issue with positioning near window or doorway?

 

If they're ajar there's a risk of the airflow just bypassing the main body of the room. 

 

From my research/experience, to achieve good air quality you need continuous mechanical ventilation.

 

DMEV achieves this by design. 

 

In our previous cottage we used to leave the kitchen extractor running all day when we were out. It made a significant difference to the dampness in the entire house so long as internal doors were left open.

 

Similarly I installed continuous mechanical ventilation in a my parents landing. Again, though is only sucking out from a central area, the whole house is fresher/dryer. 

 

I did have to make a separate silencer though as it was audible in the nighttime and when folk can hear it they turn it off. 

 

 

 

 

 

[atomsvoyage]

Thanks Iceverge. We don't have vents in the windows and tend to leave them closed most of the time in winter - is this an issue with DMEV? Or does leaving doors open and general air leakage provide enough air flow?

[JohnMo]

No surprise you have mould issues, if it not windy your ventilation rates will be next to zero.  If you put a CO2 meter in your bedrooms you would also most likely have a unhealthy level of CO2 during the night.

 

If you don't have vents above the windows, I would crack open the window, there should a way to open very slightly and close the latch/ handle.  But in the medium term look at what you could retrofit.

 

Here is good write up, their fans can be picked up a very good prices if you shop about, look for the model number as they are sold under different vendor name in the UK.

 

https://www.zehnder.co.uk/blogarticles/evolution-dmev-technology

[nod]

I used inline fans in our bathrooms 

Set n a board above the ceiling Very quiet and will clear show steam in seconds 

[atomsvoyage]

So it sounds like we need to sleep with the windows open as a starting point. Then is the following summary accurate?

DMEV Pros:

• Would improve the air quality in the rest of the house, provided bathroom doors are open and there's some inward air (from bedroom windows or elsewhere). Will not make a difference to ventilation at night when bathroom doors are closed
• Working continuously, taking out moisture from eg damp towels during the day

DMEV Cons

• Working continously, could be a noise issue and additional power consumption
• More expensive than extractor fans
• Needs a hole made in the side of the house - is this correct? I haven't seen a DMEV solution that would go into the loft with ducting

[JohnMo]

1 hour ago, atomsvoyage said:

 

DMEV Cons

• Working continously, could be a noise issue and additional power consumption
• More expensive than extractor fans
• Needs a hole made in the side of the house - is this correct? I haven't seen a DMEV solution that would go into the loft with ducting

Difficult to hear the when on.  Low energy motors so don't cost any more to run than high output normal extractor. Plenty can go in ceiling.  Quick search

 

https://www.extractorfanworld.co.uk/envirovent-eco-dmev-ht17v-zone-1-selv-continuous-ventilation-unit--humidistat--timer-4123-p.asp

[atomsvoyage]

Thanks JohnMo

 

I found this article to be informative, although it suggests that if you're only considering the bathroom it's much cheaper to have intermittent rather than continuous ventilation:

https://www.vent-axia.com/healthyhomes/simplesolution/extractfans

 

The benefits listed here are completely underwhelming to me, and none of these seem to be advantages of continuous over intermittent

https://www.eltafans.com/top-3-benefits-of-continuous-extract-fans-in-domestic-properties/

[Iceverge]

7 hours ago, atomsvoyage said:

advantages of continuous over intermittent

 

At least half of the intermittent isolators I've seen are turned off because of the racket they cause.  

 

Even if they function as designed, they leave your indoor air quality ( CO2, VOC's, humidity etc) completely to chance the rest of the time. So called "natural ventilation" is similar to hole in the roof for fresh water supply. 

 

https://passivehouseplus.ie/magazine/insight/natural-ventilation-does-it-work

 

 

 

 

 

 

[JohnMo]

Run round the show houses in your area check out the bathroom fans, we checked our local ones prior to building, dMEV was very difficult to hear.  Non dMEV made a racket.  Your choice your money