Ventilating loft to lower temperature upstairs.

FreeBear

stuart45 said:

Lofts do get incredibly hot in the summer, especially when not insulated at rafter level.

Stuck my head up in to a loft one summer that had multifoil insulation stapled to the rafters. Could only spend a few minutes up there without being cooked to a crisp.

WIAWSNB

I think I can state, with nigh-on complete certainty, that you aren't going to lower the temp of your house by any noticeable degree by increasing the ventilation in your loft.

All you can do is isolate the loft from the house as much as possible using insulation at loft floor level, and then deal with the house separately. 

justwantedtosay

WIAWSNB said:

I think I can state, with nigh-on complete certainty, that you aren't going to lower the temp of your house by any noticeable degree by increasing the ventilation in your loft.

Cooling the loft would obviously lower the temp of my bedrooms to some degree. Are you saying that pumping out the hot air wouldn't lower the temp in the loft by enough to make any difference?

GDB2222

The weather is much cooler today, and there is quite a strong breeze. So, that’s the problem solved until next year.   I’m not good at DIY but great at procrastination. 

stuart45

justwantedtosay said:

WIAWSNB said:

I think I can state, with nigh-on complete certainty, that you aren't going to lower the temp of your house by any noticeable degree by increasing the ventilation in your loft.

Cooling the loft would obviously lower the temp of my bedrooms to some degree. Are you saying that pumping out the hot air wouldn't lower the temp in the loft by enough to make any difference?

It might make some difference, but probably not enough to be noticeable. You will only really know by trying it out. 
A surface thermometer will tell you the temp of the ceiling.

WIAWSNB

stuart45 said:

justwantedtosay said:

WIAWSNB said:

I think I can state, with nigh-on complete certainty, that you aren't going to lower the temp of your house by any noticeable degree by increasing the ventilation in your loft.

Cooling the loft would obviously lower the temp of my bedrooms to some degree. Are you saying that pumping out the hot air wouldn't lower the temp in the loft by enough to make any difference?

It might make some difference, but probably not enough to be noticeable. You will only really know by trying it out. 
A surface thermometer will tell you the temp of the ceiling.

As Stuart says.
I obviously cannot suggest what difference it could make, but in a properly insulated loft, the whole point is that heat transfer is minimised between it and the house below.
And heat transfer works both ways. So if you insulate your loft correctly in order to reduce heat transfer from your home, then the very same insulation will reduce the heat transfer downwards from the loft insulation in summer. Ie, it's good for both the goose and gander. 
You insulate your loft to retain heat in your home. In winter, with the loft being at near zero temps, sometimes even below, will your ceiling feel icy cold? No, because it's insulated, thereby 'blocking' the 'cold'. But you appear to be blaming the heat in the loft for making your ceiling hot, whereas mostly it'll be due to the hot air in the bedroom.
Does the loft heat make a 'difference'? Yes, I guess it must do. But don't blame it, as the main issue is the simple fact that your loft insulation is doing the job it should - retaining heat in your rooms. 
Attempting an artificial method of driving out the hot loft air sounds expensive to me, and it's success in reducing the house temp almost certainly minimal. Instead, drive out the warm air in the actual rooms. Get a fan, or a portable air con unit.

Section62

justwantedtosay said:

WIAWSNB said:

Hi JWTS.

Almost certainly your bedroom ceilings are 'hot' from the heat in the bedroom - hot air rises - and not coming through from the loft.

That's definitely not the case.

What measurements have you done to determine this?

What is the surface temperature of the ceiling vs the still air temperature immediately below the ceiling?

justwantedtosay

WIAWSNB said:

Instead, drive out the warm air in the actual rooms. Get a fan, or a portable air con unit.

Driving out hot air with a fan would only make the room hotter, at least during the day: 

Indoor temp 27

Outdoor temp 33

27 degree air blown out of the house would have to be replaced - nature abhors a vacuum - and it could only come from outside - there is nowhere else - which would be hotter than the air being removed.

I've tried using a fan once it's less hot outside but by then the fabric of the house is hot and it has little effect. A few ounces of even icy air isn't going to lower the temp of tons of bricks and mortar, not that you could feel anyway.

Air con is beyond my means.

GDB2222

I can’t see any disadvantages in increasing the flow of air through the loft, but you ought to experiment cheaply before spending too much.

Realistically, with outside temperature of 33c, an inside temperature of 27 seems reasonable.  I wonder how much you can improve that without air conditioning. 

WIAWSNB

justwantedtosay said:

WIAWSNB said:

Instead, drive out the warm air in the actual rooms. Get a fan, or a portable air con unit.

Driving out hot air with a fan would only make the room hotter, at least during the day: 

Indoor temp 27

Outdoor temp 33

27 degree air blown out of the house would have to be replaced - nature abhors a vacuum - and it could only come from outside - there is nowhere else - which would be hotter than the air being removed.

I've tried using a fan once it's less hot outside but by then the fabric of the house is hot and it has little effect. A few ounces of even icy air isn't going to lower the temp of tons of bricks and mortar, not that you could feel anyway.

Air con is beyond my means.

In which case, how can reducing the loft heat from 40o+ down to ambient 33o possibly help?

My suggestion of a fan is not to shift the air out of the rooms, but to cool yer bod. This works, 'cos your body has inbuilt cooling systems, that the fan will assist.

Don't have a fan running unless there's someone there to be bathed in its airflow. 

I visit mil on a near daily basis. Lawdie, the heat in her bungie, as she doesn't ventilate it properly. 

However, she does have a 'Carbon', and this does cool when it aims at you. It may well be blowing 25o+ air over your body, but that added air flow evaporates your sweat, and that cools. It actually feels cool. 

Seriously, if you go to bed, spray some misty water on the oversheet, and set a fan going over it, you will chill yer t***s off. Not even water required - just set a carbon (other makes are available) running over you, and you'll be fine. Honestly.