Positive pressure unit? 17 April at 10:28AM in In my home (includes DIY) MoneySaving 11 replies 278 views

cherryblossomzel

Does anyone have any experience of positive pressure units in their homes? I live in a 1930s build and damp is a constant battle. I run a dehumidifer most of the time in winter, and in summer when I'm drying laundry. I'm wondering if a positive pressure unit will be more efficient. It's only a small 1 bed flat, so wouldn't need to be the most powerful unit available (assuming you get ones of different power). It may also help to reduce pollen inside? That would be a bonus as I do get hayfever.

Just wondering if anyone has any words of wisdom? How much should it cost to have something installed?

ashe

If you mean a PIV then they're £300-400 and then whatever your electrical charges you to install it 

don't bother with the heated units they're very expensive to run 

make sure you go through all the usual things first to eliminate condensation like checking bathroom ventilation, flaking sure no damp etc 

rob7475

I have one in our 3 bed house and it's great. We now get very little condensation (maybe a cm on the bottom of the windows during really cold spells compared to halfway up the windows before).

They cost very little to run compared to a dehumidifier.

Are you hanging laundry inside to dry or using a tumble drier? If you're hanging is up, a PIV may not help too much with the condensation created by that as you will be massively increasing the humidity in your home within a short space of time.

housebuyer143

ashe said:

If you mean a PIV then they're £300-400 and then whatever your electrical charges you to install it 

don't bother with the heated units they're very expensive to run 

make sure you go through all the usual things first to eliminate condensation like checking bathroom ventilation, flaking sure no damp etc 

I personally would say don't buy it without the heater because you won't use it in the winter as it pumps out ice cold air.
I turned mine off for this reason and will replace with a heated version if needed.

rob7475

housebuyer143 said:

ashe said:

If you mean a PIV then they're £300-400 and then whatever your electrical charges you to install it 

don't bother with the heated units they're very expensive to run 

make sure you go through all the usual things first to eliminate condensation like checking bathroom ventilation, flaking sure no damp etc 

I personally would say don't buy it without the heater because you won't use it in the winter as it pumps out ice cold air.
I turned mine off for this reason and will replace with a heated version if needed.

The heated version does barely anything. I bought the heated version but turned the heater off as it runs at 500w and makes no noticable difference to the incoming air flow. 

Mine is installed on the landing so although the landing feels a little cooler during winter, the rest of the house is fine.

housebuyer143

rob7475 said:

housebuyer143 said:

ashe said:

If you mean a PIV then they're £300-400 and then whatever your electrical charges you to install it 

don't bother with the heated units they're very expensive to run 

make sure you go through all the usual things first to eliminate condensation like checking bathroom ventilation, flaking sure no damp etc 

I personally would say don't buy it without the heater because you won't use it in the winter as it pumps out ice cold air.
I turned mine off for this reason and will replace with a heated version if needed.

The heated version does barely anything. I bought the heated version but turned the heater off as it runs at 500w and makes no noticable difference to the incoming air flow. 

Mine is installed on the landing so although the landing feels a little cooler during winter, the rest of the house is fine.

Hmmm that's interesting to know as 500w is a lot of money over time and if it's not much warmer, then what's the point. 
Might need to rethink this 🤔 it might be warmer but then I won't use it due to cost 😆

cherryblossomzel

Interesting re heated vs non-heated. The flat I live in does tend to be cold, even in summer, so on the one hand I'm loath to pump it full of even more cold air. However, if it is significantly more expensive to run, then maybe I'm better off just using the dehumidifier as I am at the moment. Or just getting the non-heated version, and being careful with placement, I would probably install it in the entrance hallway, which is the most central location in the flat.

housebuyer143 - when you say it's putting our freezing cold air - do you mean that if you stand underneath it, it feels like an air conditioner?

housebuyer143

cherryblossomzel said:

Interesting re heated vs non-heated. The flat I live in does tend to be cold, even in summer, so on the one hand I'm loath to pump it full of even more cold air. However, if it is significantly more expensive to run, then maybe I'm better off just using the dehumidifier as I am at the moment. Or just getting the non-heated version, and being careful with placement, I would probably install it in the entrance hallway, which is the most central location in the flat.

housebuyer143 - when you say it's putting our freezing cold air - do you mean that if you stand underneath it, it feels like an air conditioner?

Yes, when the weather outside is cold, it literally pulls air from the loft space which is the outside temp and pumps it into the house, in our case the hallway. 
As you can imagine when it's snowing outside and you are desperately trying to heat up your house then you have this fan blowing in literally freezing air.  It's completely counterproductive.
 Then you have the reverse problem in the summer, you are trying to keep the house cool on really hot days by keeping the windows closed and you have this PIV pumping in scorching air from the loft. 
Not sure the solution as in theory they are a good idea, but practically they are not great. 
I'm going to see if I can find a heated one that is cheaper to run...

rob7475

housebuyer143 said:

cherryblossomzel said:

Interesting re heated vs non-heated. The flat I live in does tend to be cold, even in summer, so on the one hand I'm loath to pump it full of even more cold air. However, if it is significantly more expensive to run, then maybe I'm better off just using the dehumidifier as I am at the moment. Or just getting the non-heated version, and being careful with placement, I would probably install it in the entrance hallway, which is the most central location in the flat.

housebuyer143 - when you say it's putting our freezing cold air - do you mean that if you stand underneath it, it feels like an air conditioner?

Yes, when the weather outside is cold, it literally pulls air from the loft space which is the outside temp and pumps it into the house, in our case the hallway. 
As you can imagine when it's snowing outside and you are desperately trying to heat up your house then you have this fan blowing in literally freezing air.  It's completely counterproductive.
 Then you have the reverse problem in the summer, you are trying to keep the house cool on really hot days by keeping the windows closed and you have this PIV pumping in scorching air from the loft. 
Not sure the solution as in theory they are a good idea, but practically they are not great. 
I'm going to see if I can find a heated one that is cheaper to run...

The bit about pumping hot air in in summer shouldn't be an issue. Most PIV units detect when the loft air temp is above say 25 degreest, the unit cuts off. When the outside temperature is warm, condensation shouldn't be a problem so there's no need for the PIV unit to be running.

consumers_revenge

yep it can start turning off anywhere after the loft temp get above 18 degress.

we have the heated version and it comes on if its below 7 degrees in the loft. it will raise the temperature coming out by about 2 degrees so up to 9 in the 7 degrees example. Its not a constant 500w mind as its 'pulse' generating and dont forget the air coming in is from the loft space, so the loft is warmer than directly outside. Unless its freezing outside then I dont tend to bother turning the heating element on.

does it work? yes provided the internal doors are cracked open just a bit (1cm) or have a gap underneath I can say about 97% of the condensation in now gone in my house. And we used to have to karscher vacuum the windows daily from half way down. RH has dropped by 25-40%

if its for a flat you want the nuaire flatmaster rather than the drimaster

ashe

housebuyer143 said:

ashe said:

If you mean a PIV then they're £300-400 and then whatever your electrical charges you to install it 

don't bother with the heated units they're very expensive to run 

make sure you go through all the usual things first to eliminate condensation like checking bathroom ventilation, flaking sure no damp etc 

I personally would say don't buy it without the heater because you won't use it in the winter as it pumps out ice cold air.
I turned mine off for this reason and will replace with a heated version if needed.

Opposite imo. The temp difference isn't huge according to most owners, and in another thread a user did two days of running it with it off and On and it recorded £3 usage for one day I believe but he said there was barely any temperature difference in the air coming in.

the other alternative usually suggested is to open windows at night and that will also introduce cold air so no different doing that to me.