Electric fans to ventilate loft space
Discussion
At about this time of year I occasionally wonder if actively ventilating the loft in a house would help with lowering temperatures in the rooms with lofts above. I was thinking something along the lines of a fan in the soffit at either end of each loft or even better one blowing out at the apex and one in at the soffit.
Has anyone tried this? I've just wandered upstairs and the ceiling doesn't feel noticeably warmer to the touch than the walls but that's not particularly scientific. Will give it a go with LASER thermometer in a bit.
Has anyone tried this? I've just wandered upstairs and the ceiling doesn't feel noticeably warmer to the touch than the walls but that's not particularly scientific. Will give it a go with LASER thermometer in a bit.
Richard-D said:
I was thinking something along the lines of a fan in the soffit at either end of each loft or even better one blowing out at the apex and one in at the soffit.
Best option will be to just extract the hot air and not try to add positive inlet?Ideally you'd draw air from the highest point(s) and vent that out, fan doesn't need to that high as it could feed from duct.
Leave the soffits as-is, assuming ghey have some level of ventilation they should act as just passive inlets for the whole space.
Not sure what size extraction you'd want, suspect anything too small wouldn't do anything useful given the rate heat can be absorbed by a roof and you'd be better with something large run intermittently than something small run continously.
JoshSm said:
Best option will be to just extract the hot air and not try to add positive inlet?
Ideally you'd draw air from the highest point(s) and vent that out, fan doesn't need to that high as it could feed from duct.
Leave the soffits as-is, assuming ghey have some level of ventilation they should act as just passive inlets for the whole space.
Not sure what size extraction you'd want, suspect anything too small wouldn't do anything useful given the rate heat can be absorbed by a roof and you'd be better with something large run intermittently than something small run continously.
Good point about the inlet. As you say, that shouldn't need anything other than ensuring soffit vents are clear (which should already be the case).Ideally you'd draw air from the highest point(s) and vent that out, fan doesn't need to that high as it could feed from duct.
Leave the soffits as-is, assuming ghey have some level of ventilation they should act as just passive inlets for the whole space.
Not sure what size extraction you'd want, suspect anything too small wouldn't do anything useful given the rate heat can be absorbed by a roof and you'd be better with something large run intermittently than something small run continously.
GetCarter said:
Fans just move hot air around.
Is that a technical view? A desk fan moves air around. An extractor fan would move hot air from inside (heated by the sun on the tiles) to be replaced by cooler air from outside. Loft space could reach 50/60C so well above external air temperatures.I can understand some of this being trickier to contemplate from the far north.
If the loft isn't habitable you should have sufficient insulation in the floor that any heat up there doesn't affect the rooms below.
The tiles will be a massive thermal store so any venting won't do much.
That said, heat obviously rises so if you can get it to move up from rooms which are lived in it will help a bit.
The tiles will be a massive thermal store so any venting won't do much.
That said, heat obviously rises so if you can get it to move up from rooms which are lived in it will help a bit.
Richard-D said:
wonder if actively ventilating the loft in a house would help with lowering temperatures in the rooms with lofts above. I was thinking something along the lines of a fan in the soffit at either end of each loft or even better one blowing out at the apex and one in at the soffit.
I've often had exactly the same thought. A couple of big round fans in the gables, one blowing "in" and the other blowing "out". Obviously some sort of insulated shutter mechanism attached so that when the fans are off the shutters are shut.I ended up installing A/C instead. Yesterday the bedroom temp hit 93F before the A/C was switched on. So much heat in the attic above.
A vented ridge would help together with well vented soffits I’d guess.
Or a remote bathroom extractor kit with the extract hose up underneath the ridge pumping out of a vent in the soffit controlled by a mechanical dial type thermostat.
Or, or… fit the ridge with a large piano hinge and have the roof lift up on hydraulic actuators for venting.
I have not thought this through as the water tightness of any gutter down pipes would clearly cause a problem with my plan.
Or a remote bathroom extractor kit with the extract hose up underneath the ridge pumping out of a vent in the soffit controlled by a mechanical dial type thermostat.
Or, or… fit the ridge with a large piano hinge and have the roof lift up on hydraulic actuators for venting.
I have not thought this through as the water tightness of any gutter down pipes would clearly cause a problem with my plan.
If the ceiling is properly insulated and air-sealed it won’t make a dramatic difference below. But if loft heat is bleeding
into the rooms because the insulation/air-sealing is weak or the thermal envelope is compromised for whatever reason, then reducing the loft temperature absolutely can help.
In the US and other places that get insanely hot attics which often have HVAC ducts etc in, attic fans are more common, but they're for extraction and higher up towards the apex. Soffits are generally for air admittance not egress.
into the rooms because the insulation/air-sealing is weak or the thermal envelope is compromised for whatever reason, then reducing the loft temperature absolutely can help.
In the US and other places that get insanely hot attics which often have HVAC ducts etc in, attic fans are more common, but they're for extraction and higher up towards the apex. Soffits are generally for air admittance not egress.
I have a bluetooth temperature logger in my loft.
The centre of the loft was getting to 40degC in the week, but really not much sign of that on the ceilings below, an IR thermometer tells me the ceilings are the same temperature as the tops of the walls.
I do have around 250mm of rockwool and I've paid some attention to avoiding air flow between loft and rooms.
That's with some sort of vents at the ridge.
I think you'd need a fairly powerful fan to draw the hot air down from the ridge area if there were no vents there?
Maybe the thermal airflow from a vent high up could drive a small turbine? :-)
The centre of the loft was getting to 40degC in the week, but really not much sign of that on the ceilings below, an IR thermometer tells me the ceilings are the same temperature as the tops of the walls.
I do have around 250mm of rockwool and I've paid some attention to avoiding air flow between loft and rooms.
That's with some sort of vents at the ridge.
I think you'd need a fairly powerful fan to draw the hot air down from the ridge area if there were no vents there?
Maybe the thermal airflow from a vent high up could drive a small turbine? :-)
A few years back I thought about fitting a fan into a loft hatch sized frame, then running it at night. At the time the outside air was nice and cool, but even with the windows open the bedroom temps were much higher, and the loft space even more so.
The idea was that it would move the hot bedroom air into the loft space to displace the even hotter air (cooling the loft) and cool outside air would be drawn into the bedrooms via the open windows.
I never got round to doing it, but I might resurrect the idea. We are already using fans in the bedrooms but thats just moving hot air about.
Checking my smart thermometers the house didn't drop below 25 degrees last night, but the external air was 21 degrees at 22:00 and was 18 at 04:00. I got up at 6 because I was too hot.
The idea was that it would move the hot bedroom air into the loft space to displace the even hotter air (cooling the loft) and cool outside air would be drawn into the bedrooms via the open windows.
I never got round to doing it, but I might resurrect the idea. We are already using fans in the bedrooms but thats just moving hot air about.
Checking my smart thermometers the house didn't drop below 25 degrees last night, but the external air was 21 degrees at 22:00 and was 18 at 04:00. I got up at 6 because I was too hot.
Edited by 98elise on Sunday 28th June 09:06
98elise said:
A few years back I thought about fitting a fan into a loft hatch sized frame, then running it at night. At the time the outside air was nice and cool, but even with the windows open the bedroom temps were much higher, and the loft space even more so.
The idea was that it would move the hot bedroom air into the loft space to displace the even hotter air (cooling the loft) and cool outside air would be drawn into the bedrooms via the open windows.
I never got round to doing it, but I might resurrect the idea. We are already using fans in the bedrooms but thats just moving hot air about.
Checking my smart thermometers the house didn't drop below 25 degrees last night, but the external air was 21 degrees at 22:00 and was 18 at 04:00. I got up at 6 because I was too hot.
Can you not get some of that cool outdoor air into the house?The idea was that it would move the hot bedroom air into the loft space to displace the even hotter air (cooling the loft) and cool outside air would be drawn into the bedrooms via the open windows.
I never got round to doing it, but I might resurrect the idea. We are already using fans in the bedrooms but thats just moving hot air about.
Checking my smart thermometers the house didn't drop below 25 degrees last night, but the external air was 21 degrees at 22:00 and was 18 at 04:00. I got up at 6 because I was too hot.
Edited by 98elise on Sunday 28th June 09:06
OutInTheShed said:
Can you not get some of that cool outdoor air into the house?
Windows were on vent but it's not enough, plus the house has thermal mass (your walls are just big radiators).By mechanically forcing the warm room air onto the loft, it will be replaced with cool air from outside. The loft is also now cooler removing a huge heat source.
trickywoo said:
If the loft isn't habitable you should have sufficient insulation in the floor that any heat up there doesn't affect the rooms below.
The tiles will be a massive thermal store so any venting won't do much.
That said, heat obviously rises so if you can get it to move up from rooms which are lived in it will help a bit.
There is nowhere near enough loft insulation in the 2 storey end of our house (house is 2 storey at one end with a long single storey section). Obviously this also needs remedying. If this is only worthwhile in poorly insulated homes then the answer is of course to just insulate properly and ignore the loft ventilation idea. The tiles will be a massive thermal store so any venting won't do much.
That said, heat obviously rises so if you can get it to move up from rooms which are lived in it will help a bit.
Panamax said:
I've often had exactly the same thought. A couple of big round fans in the gables, one blowing "in" and the other blowing "out". Obviously some sort of insulated shutter mechanism attached so that when the fans are off the shutters are shut.
I ended up installing A/C instead. Yesterday the bedroom temp hit 93F before the A/C was switched on. So much heat in the attic above.
Yes, A/C is the real solution. I bet we're all going to be fitting that over the next few years anyway. If you can reduce the load on the A/C by spending £20 making the loft cooler there could potentially be a gain to be had there too.I ended up installing A/C instead. Yesterday the bedroom temp hit 93F before the A/C was switched on. So much heat in the attic above.
andy43 said:
A vented ridge would help together with well vented soffits I d guess.
Or a remote bathroom extractor kit with the extract hose up underneath the ridge pumping out of a vent in the soffit controlled by a mechanical dial type thermostat.
Or, or fit the ridge with a large piano hinge and have the roof lift up on hydraulic actuators for venting.
I have not thought this through as the water tightness of any gutter down pipes would clearly cause a problem with my plan.
Lol, now you're thinking. I wasn't aware Colin Furze was on Pistonheads.Or a remote bathroom extractor kit with the extract hose up underneath the ridge pumping out of a vent in the soffit controlled by a mechanical dial type thermostat.
Or, or fit the ridge with a large piano hinge and have the roof lift up on hydraulic actuators for venting.
I have not thought this through as the water tightness of any gutter down pipes would clearly cause a problem with my plan.
Your initial suggestion is more in line with what I had in mind.
Mr Pointy said:
Search for full or whole house ventilation - if you look at the image search you'll see suggestions of how it's done elsewhere.
Thanks for the pointer. Lots of good solutions there but they are all centered around a structure that's different to the typical UK house.Stu R said:
If the ceiling is properly insulated and air-sealed it won t make a dramatic difference below. But if loft heat is bleeding
into the rooms because the insulation/air-sealing is weak or the thermal envelope is compromised for whatever reason, then reducing the loft temperature absolutely can help.
In the US and other places that get insanely hot attics which often have HVAC ducts etc in, attic fans are more common, but they're for extraction and higher up towards the apex. Soffits are generally for air admittance not egress.
Appreciate that soffits aren't usually used that way but if you can make it work then no reason not to. I was leaning that way because making a big hole in the gable end is more work and more difficult to undo. into the rooms because the insulation/air-sealing is weak or the thermal envelope is compromised for whatever reason, then reducing the loft temperature absolutely can help.
In the US and other places that get insanely hot attics which often have HVAC ducts etc in, attic fans are more common, but they're for extraction and higher up towards the apex. Soffits are generally for air admittance not egress.
OutInTheShed said:
I have a bluetooth temperature logger in my loft.
The centre of the loft was getting to 40degC in the week, but really not much sign of that on the ceilings below, an IR thermometer tells me the ceilings are the same temperature as the tops of the walls.
I do have around 250mm of rockwool and I've paid some attention to avoiding air flow between loft and rooms.
That's with some sort of vents at the ridge.
I think you'd need a fairly powerful fan to draw the hot air down from the ridge area if there were no vents there?
Maybe the thermal airflow from a vent high up could drive a small turbine? :-)
Interested that you've already had a look with an IR thermometer. Although, the top of the walls being the same temperature as the ceiling may not be a good test. Could those walls be warmer at the top because of the excessive loft heat?The centre of the loft was getting to 40degC in the week, but really not much sign of that on the ceilings below, an IR thermometer tells me the ceilings are the same temperature as the tops of the walls.
I do have around 250mm of rockwool and I've paid some attention to avoiding air flow between loft and rooms.
That's with some sort of vents at the ridge.
I think you'd need a fairly powerful fan to draw the hot air down from the ridge area if there were no vents there?
Maybe the thermal airflow from a vent high up could drive a small turbine? :-)
On the fan power required to push hot air down...yes that's something I was wondering about I think you'd need to test to know if it would be effective.
98elise said:
A few years back I thought about fitting a fan into a loft hatch sized frame, then running it at night. At the time the outside air was nice and cool, but even with the windows open the bedroom temps were much higher, and the loft space even more so.
The idea was that it would move the hot bedroom air into the loft space to displace the even hotter air (cooling the loft) and cool outside air would be drawn into the bedrooms via the open windows.
I never got round to doing it, but I might resurrect the idea. We are already using fans in the bedrooms but thats just moving hot air about.
Checking my smart thermometers the house didn't drop below 25 degrees last night, but the external air was 21 degrees at 22:00 and was 18 at 04:00. I got up at 6 because I was too hot.
These things feel like they might be potentially little more than marginal gains. A few marginal gains that can be made at minimal cost with a little time and effort might not be a waste of time though.The idea was that it would move the hot bedroom air into the loft space to displace the even hotter air (cooling the loft) and cool outside air would be drawn into the bedrooms via the open windows.
I never got round to doing it, but I might resurrect the idea. We are already using fans in the bedrooms but thats just moving hot air about.
Checking my smart thermometers the house didn't drop below 25 degrees last night, but the external air was 21 degrees at 22:00 and was 18 at 04:00. I got up at 6 because I was too hot.
JoshSm said:
Is that a technical view? A desk fan moves air around. An extractor fan would move hot air from inside (heated by the sun on the tiles) to be replaced by cooler air from outside. Loft space could reach 50/60C so well above external air temperatures.
I can understand some of this being trickier to contemplate from the far north.
They're certainly a thing in the US - you see some houses with massive fans in the roof gable. Might get some ideas searching US pages.I can understand some of this being trickier to contemplate from the far north.
Sheepshanks said:
JoshSm said:
Is that a technical view? A desk fan moves air around. An extractor fan would move hot air from inside (heated by the sun on the tiles) to be replaced by cooler air from outside. Loft space could reach 50/60C so well above external air temperatures.
I can understand some of this being trickier to contemplate from the far north.
They're certainly a thing in the US - you see some houses with massive fans in the roof gable.I can understand some of this being trickier to contemplate from the far north.
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