Positive Input Ventilation opinions please?

Nugsy88 · 29 Nov 2021 at 15:14

Bug One said:
If all vents and windows are shut, where is the air going to? Into the loft I expect. You're not going to remove any moisture if the air has nowhere to go.

I think you are over estimating the air tightness of a 90s house. Just window vents are closed, not extractor fans etc

b0rn2sk8 · 29 Nov 2021 at 15:20

Houses are far from air tight, the air will find places to escape.

Modern houses are most definitely not air tight. They’ll have extractors in the kitchen and any bathrooms.

robj20 · 8 Jan 2022 at 12:12

About ready to order one, part of me still thinks all its going to do is blow air straight through the bathroom and not reach any other rooms especially downstairs.
Looking at the link-hc version so I can have the boost switch as well.

b0rn2sk8 · 8 Jan 2022 at 12:46

What's the benefit of these over say a heat recovery ventilator system?

Molep · 8 Jan 2022 at 14:22

https://www.bpcventilation.com/blog/do-heat-recovery-systems-work/

https://www.bpcventilation.com/what-is-positive-ventilation

b0rn2sk8 · 8 Jan 2022 at 14:26

well yes, I know how each system works but I was more inerested in why you would pick one system over another

SoliD · 8 Jan 2022 at 16:06

You'll be surprised @robj20 they are very effective!

Siliconslave · 10 Jan 2022 at 10:02

Heat recovery looks to be a better overall solution, but costs significantly more to purchase and install. The benefits of PIV seem to be you get a good chunk of the 'fresh air' benefits at a fraction of the cost.

New airtight homes are recommended to install a heat recovery ventilation system (MVHR) and not a positive ventilation unit (PIV).

dirtychinchilla · 12 Jan 2022 at 11:04

MVHR is a no brainer. If you have fresh air entering the property without pre-heat or heat recovery, it will enter at the same temperature as the air outside, causing a draught. If you're also extracting air, you're extracting heat from the building. Why not cooridnate both to warm incoming air and reduce energy consumption due to heat loss?

Siliconslave · 12 Jan 2022 at 11:26

dirtychinchilla said:
Why not cooridnate both to warm incoming air and reduce energy consumption due to heat loss?

As i say the cost of installation will be the real limiting factor - I can cut a hole in the ceiling and wire a plug in pretty easily but putting a load of piping into the loft may be more of a challenge (and cost) - would the long term benefit be worth the additional cost.

The systems seem to be about 5-10x that of the PIV systems and on a multi-story period property it'd be a nightmare to route all the tubing for a proper MVHR - guess I could do the upstairs pretty easily but would that really offer much of a benefit?

dirtychinchilla · 12 Jan 2022 at 11:49

Siliconslave said:
As i say the cost of installation will be the real limiting factor - I can cut a hole in the ceiling and wire a plug in pretty easily but putting a load of piping into the loft may be more of a challenge (and cost) - would the long term benefit be worth the additional cost.

The systems seem to be about 5-10x that of the PIV systems and on a multi-story period property it'd be a nightmare to route all the tubing for a proper MVHR - guess I could do the upstairs pretty easily but would that really offer much of a benefit?

Fully agree. Putting in a ducted MVHR unit would involve a lot more work. I often think about it, with a comfort cooling coil on. But it would be loads of work and not cheap.

Comfort-wise, you'd probably have a decent improvement. I don't think the ROI would be very good though, at least until energy prices reach a sensible (higher) level in the UK.

SoliD · 12 Jan 2022 at 16:07

For that cost uplift i'd rather have Split AC for the additional cost again over MVHR.

dirtychinchilla · 13 Jan 2022 at 11:30

SoliD said:
For that cost uplift i'd rather have Split AC for the additional cost again over MVHR.

AC doesn't provide any fresh air.

Buffman · 13 Jan 2022 at 11:42

I've had it before (nuaire drimaster like the above photos) it did reduce condensation significantly. Only thing was there was a slight loft smell (possibly due to proximity to floor but it was a very tight loft space)

SoliD · 13 Jan 2022 at 12:18

dirtychinchilla said:
AC doesn't provide any fresh air.

but it will clean and dry the air and provide necessary circulation to it in the house.

panthro · 13 Jan 2022 at 12:40

What's the difference between this and a dehumidifier? We have condensation 3 out of the 4 bedrooms in the winter but the dehumidifier has solved this mostly unless it's below zero. We have no mould issues though except when the bathroom extractor broke without me realising.

dirtychinchilla · 13 Jan 2022 at 13:15

SoliD said:
but it will clean and dry the air and provide necessary circulation to it in the house.

AC doesn't typically clean the air. If you wanted all singing all dancing then the best thing would be MVHR with heating/cooling capacity.

Doobedoo · 13 Jan 2022 at 13:20

panthro said:
What's the difference between this and a dehumidifier? We have condensation 3 out of the 4 bedrooms in the winter but the dehumidifier has solved this mostly unless it's below zero. We have no mould issues though except when the bathroom extractor broke without me realising.

Electricity usage will be the biggest factor. Piv is literally just a fan where as a dehumidifier will consume 150-500 watts depending on size and type.

Dehumidifier also removes moisture from the air where as a piv just circulates air.

Adam_151 · 14 Jan 2022 at 00:01

Siliconslave said:
Heat recovery looks to be a better overall solution, but costs significantly more to purchase and install. The benefits of PIV seem to be you get a good chunk of the 'fresh air' benefits at a fraction of the cost.

Just to puit my 2p, while they do say that MVHR is not recommend for older properties that arn't to mordern air tighteness standards, and can see how this breaks the theory of the thing on paper in terms of energy savings etc. But I have an an older property that some of if is solid walls etc, the biggest place I used to get an issue through was windows, in winter you'd wake up and there would be enough water on the windows to leave a towel sodden after you'd wiped them all. Considered PIV as well as MVHR and went for MVHR and the window issue went away, and I have to open windows less which must be saving me energy over doing that (although not in the perfect way perfect airtightness and MVHR would on paper...)

Extra ventilation is required in rooms that make a lot of condensation suddently, like high flow shower in bathroom, MVHR cant be expected to coe with all though.

Lukily as its a bungalow and all the rooms requiring extraction where along the back of the property and all though requiring air inlet were at the front, it was not too difficult ducting wise.

Still need to sort the speed control, its running at its fastest speed with no set back at present, which is adding a little to the bills and is on the list to sort!