PIV questions and PIV vs traditional extractor fans

[John74813]

Hi all

I live in a detached house built in 2006. Most rooms have trickle vents above the windows and there are extractor fans with timers in the bathrooms and utility room (5 of these in total)

While I don't have problems with condensation, I am interested mechanical ventilation for the benefits to indoor air quality.

I've read a lot about PIV system which I think could work well in my house. However, my concern would be the loft gets incredibly hot in Summer.. Can the PIV unit be connected to ducting that goes out of the roof (replacing a roof tile with a roof vent)?

As I already have several extraction points throughout the house, could I in theory achieve a similar goal by having some/all of the extraction points set to be permanently on? Air would then be drawn in through trickle vents and expelled through the extractor fans.

Any thoughts please much appreciated

Thanks
John

 

[pcaouolte]

When the loft gets incredibly hot in the summer the PIV will shut down. It will start up again when the loft cools down, usually overnight. Some days & nights in the summer the PIV won't come on at all, these are the days where it is not needed because the air inside the home will already be dry, you can open windows at these times if necessary.

Don't duct the PIV to outside, you want the dry warm air from the loft, not the cold wet air from outside.

I don't think that you will achieve a similar effect with extraction. The air that the PIV supplies is filtered and blown into the home, extractors are unlikely to be able to draw air into the home through a filter.

 

[John74813]

Hi thanks for your response. I appreciate the air from the PIV is filtered but if it’s not in use during hot summers then the air coming in through the open windows will also not be filtered (as would the air coming through trickle vents).

Is there a particular need for the incoming air to be filtered that I may have overlooked? We don’t live in a densely populated area so not worried about external particulates

 

[pcaouolte]

I thought that you were trying to improve the indoor air quality rather than pump in dust, pollen and insects from outside?

 

[John74813]

Air quality as in co2 and pm2.5/pm10 particulates which generally measure better outside than inside.

My only reservations with the PIV would be the inability to use it for most of the Summer. If this house is anything like my last, the loft was sweltering hot. I could indeed open windows for airflow but will have the same problem of pollen and dust.

 

[BlueLoo]

PIV?
I've obviously spent too much time on Reddit.....

 

[pcaouolte]

PIV?

Positive Input Ventilation.
https://www.nuaire.co.uk/residentia...positive-input-ventilation-systems-piv-nuaire

 

[pcaouolte]

Air quality as in co2 and pm2.5/pm10 particulates which generally measure better outside than inside.

My only reservations with the PIV would be the inability to use it for most of the Summer. If this house is anything like my last, the loft was sweltering hot. I could indeed open windows for airflow but will have the same problem of pollen and dust.

I've just looked back through my energy monitoring and last summer my PIV had 13 days where it did not come on at all, I wouldn't call that "most of the Summer". My roof has dark brown tiles which absorb a lot of heat from the sun so I expect that my loft gets as hot as most. As the PIV draws outside air into the loft before pushing it into the house it does tend to keep the loft a bit cooler.

 

[John74813]

Ok, thanks for checking. Yes, you're right about the PIV drawing in the outside air therefore keeping the loft cooler in general. I might give it a go then. Do you have one with a heating element as well?

As I understand it, the duct will go down and exit through the ceiling of the landing. Is there any "tuning" required in terms of which trickle vents to leave open (and by how much) in order to get the air flowing through the house as much as possible? I'd be concerned that the air would only make it as far as the upstairs rooms and not down into the kitchen etc. I guess you'd need to check whether air is coming IN to the trickle vents or out. I guess I'd also keep the existing room extractor fans as they currently are? (on a ~10min timer)

Edit: Other thing of concern is I can't seem to see any ventilation in the eaves of the loft. I would therefore assume that the roof felt is breathable but do not know how to validate that. There is no condensation in the loft but the insulation is only 100mm

 

[JohnD]

In hot, sunny weather, you can open the loft hatch and hot air from the house will rise into it. This relies on eaves ventilation so it can escape. Results are best if you have an opening on the shaded side of the house for fresh air to enter. Otherwise there will just be adventitious ventilation from various gaps. No fan is necessary.

You should be able to see daylight in the eaves, with the loft insulation trimmed to cover the ceilings below. Some people incorrectly stuff it into the eaves. It is easily corrected using a breadknife or wallpapering scissors. Wear a dust mask, especially if you have the old yellow fibreglass insulation.

 

[JohnD]

Don't duct the PIV to outside, you want the dry warm air from the loft, not the cold wet air from outside.

This is incorrect. Cold, wet, outdoor air contains less water vapour, and less dust and contaminants, than warm indoor air.

 

[pcaouolte]

This is incorrect. Cold, wet, outdoor air contains less water vapour, and less dust and contaminants, than warm indoor air.

If it is incorrect, which it isn't, then why do the makers of PIV units design them to get their air supply from the loft rather than outside?

The air in the loft is not warm indoor air, any openings from the house to the loft should be sealed when installing a PIV unit. The air in the loft is outdoor air warmed by the sun.

 

[pcaouolte]

Ok, thanks for checking. Yes, you're right about the PIV drawing in the outside air therefore keeping the loft cooler in general. I might give it a go then. Do you have one with a heating element as well?

As I understand it, the duct will go down and exit through the ceiling of the landing. Is there any "tuning" required in terms of which trickle vents to leave open (and by how much) in order to get the air flowing through the house as much as possible? I'd be concerned that the air would only make it as far as the upstairs rooms and not down into the kitchen etc. I guess you'd need to check whether air is coming IN to the trickle vents or out. I guess I'd also keep the existing room extractor fans as they currently are? (on a ~10min timer)

Edit: Other thing of concern is I can't seem to see any ventilation in the eaves of the loft. I would therefore assume that the roof felt is breathable but do not know how to validate that. There is no condensation in the loft but the insulation is only 100mm

I do have a PIV with a heating element. The heater usually comes on when outside temperatures are below 6 degrees. It doesn't make the incoming air feel warm, just a bit less cold.

The duct goes down through the ceiling of the landing. The incoming air does travel a surprising distance around the house. I don't have any trickle vents. I do have extractor fans working exactly as they were before the PIV was installed.

Loft spaces are not usually sealed from the outside air even when there are no eaves vents. Stick your head in the loft on a windy day.

 

[John74813]

Great, thanks for all the info. Interestingly, I found this "Nuaire Drimaster 365" which does in fact take air in from the outside, but only when the loft is too hot. The only downside I can see to this model though is it doesn't contain a heating element.

Will have a look in the loft on a windy day to check for air flow, good idea.

 

[pcaouolte]

Interestingly, I found this "Nuaire Drimaster 365" which does in fact take air in from the outside, but only when the loft is too hot. The only downside I can see to this model though is it doesn't contain a heating element.

Interesting. I hadn't seen that model before, perhaps it is new. On balance I think I would stick with the ones that take air from the loft and accept that for about 14 days of the year they don't work ,to avoid having to install the extra ducting to outside. YMMV.