Crofter Posted January 15, 2017 Share Posted January 15, 2017 I've come across some discussion of this on other forums (fora?) and am at a stage with my built where it would be possible to do this test now. I have installed all my internal PUR insulation and foamed up any gaps as best I can, so a test now will reveal any major leaks in advance of installing the vapour/airtightness layer. I would then run the test a second time to check that the barrier was doing its job. It seems that the general idea is to use a large car fan running off a 12v battery, to suck air out of the house. A tube set up with one end in the house, and one outside, can function as a manometer to check the pressure differential. So far, so good. But on a practical note, how would I actually go about finding the leaks? Just work my way along every joint and edge feeling for a draft- or something a bit more scientific? I was in the house foaming up gaps the other day when the wind was gusting to 60mph outside... is a DIY fan test going to achieve anything that I haven't already done with the help of mother nature? Link to comment Share on other sites More sharing options...
joe90 Posted January 15, 2017 Share Posted January 15, 2017 A smoke gun/generator springs to mind but our friend Jeremy has done a lot on this subject. Link to comment Share on other sites More sharing options...
PeterW Posted January 15, 2017 Share Posted January 15, 2017 Cheap vape generator from a pound shop will produce smoke that will show up any draughts. Link to comment Share on other sites More sharing options...
ProDave Posted January 15, 2017 Share Posted January 15, 2017 I have been pondering this. I believe I have a large mains powered fan on the way (15" diameter fan) so you can run the fan and measure the pressure difference between inside and out. BUT there is a "missing link" to actually measure the leakage. In a perfect house, once a certain pressure difference is achieved, there will be no air flow through the fan? is that right? So to measure leakage into the house you must measure the air flow exiting through the fan. Anemometer? or will the flow be to low for that? without that measurement, yes you can suck air out and go looking for obvious leaks, but you have no measure of how good it is. Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 15, 2017 Share Posted January 15, 2017 Pressurising the building instead of creating a vacuum would be better for the initial test. Using artificial smoke ( flue test smoke bomb or smoke matches / smoke detector tester aerosol ) to find leaks would be much better IMO. You pressurise the building and just go around watching where the smoke exists the various junctions / points of the house and mark them off accordingly to repair later. When your choking to death on the thick putrid smoke your good to go ? Link to comment Share on other sites More sharing options...
NSS Posted January 15, 2017 Share Posted January 15, 2017 Probably a dumb idea, but I was actually wondering whether I could do a rough test for leaks by running the MVHR with the main inlet covered? Concern is whether this could potentially damage the unit? Link to comment Share on other sites More sharing options...
SteamyTea Posted January 16, 2017 Share Posted January 16, 2017 7 hours ago, NSS said: Probably a dumb idea It will depend on how the fan motor is cooled. If it relies on the incoming air, then it will be a problem. Not sure if you will get enough flow though the system to raise the pressure enough, but that is your you to find out. From an academic viewpoint, I think pressure testing should be both positive and negative. This will test any mechanical seals better (I have "V" seals on my back door). Also, testing should be repeated a few times over a period of time. One of the basic of good science is hypothesis testing and repeatability. Link to comment Share on other sites More sharing options...
Guest Alphonsox Posted January 16, 2017 Share Posted January 16, 2017 9 hours ago, Crofter said: So far, so good. But on a practical note, how would I actually go about finding the leaks? Just work my way along every joint and edge feeling for a draft- or something a bit more scientific? I was present when we had our build officially measured - No need for smoke or anything complex, you can easily feel a draft in a close to airtight build. All we did was to wander around the place with some tape and check ever joint by hand. After half an hour of remedial patching we had covered the whole place and ended up with a very good final result. Link to comment Share on other sites More sharing options...
Nickfromwales Posted January 16, 2017 Share Posted January 16, 2017 15 minutes ago, Alphonsox said: I was present when we had our build officially measured - No need for smoke or anything complex, you can easily feel a draft in a close to airtight build. All we did was to wander around the place with some tape and check ever joint by hand. After half an hour of remedial patching we had covered the whole place and ended up with a very good final result. That's annoyingly easy and un-complicated Link to comment Share on other sites More sharing options...
Onoff Posted January 16, 2017 Share Posted January 16, 2017 1 hour ago, Alphonsox said: I was present when we had our build officially measured - No need for smoke or anything complex, you can easily feel a draft in a close to airtight build. All we did was to wander around the place with some tape and check ever joint by hand. After half an hour of remedial patching we had covered the whole place and ended up with a very good final result. Nothing like to the degree of air tightness being adhered to here but in doing one room (the bathroom) I've now put a taped vcl on 2 1/2 walls which were air leaky either through holes, mortar joints, cracked plaster etc. It's so noticable as I work my way round. The draught now comes from / is focused on the wet room corner & where the soil pipe comes in. I reckon I could close my eyes and navigate to it by touch. The downside is if I "drop one" and the missus walks in! It just lingers! Roll on the single room MVHR! Link to comment Share on other sites More sharing options...
PeterW Posted January 16, 2017 Share Posted January 16, 2017 1 hour ago, Alphonsox said: I was present when we had our build officially measured - No need for smoke or anything complex, you can easily feel a draft in a close to airtight build. All we did was to wander around the place with some tape and check ever joint by hand. After half an hour of remedial patching we had covered the whole place and ended up with a very good final result. The reason for a negative pressure testing is that air infiltration can come via the cavity so a positive pressure test would not show where the leaks were going to. The correct test measurement method looks at the power input to the fan and maps that against the pressure in the building - the harder the fan has to work (ie the increase in current) the more air tight the building. Link to comment Share on other sites More sharing options...
jack Posted January 16, 2017 Share Posted January 16, 2017 1 hour ago, SteamyTea said: From an academic viewpoint, I think pressure testing should be both positive and negative. This will test any mechanical seals better (I have "V" seals on my back door). Also, testing should be repeated a few times over a period of time. One of the basic of good science is hypothesis testing and repeatability. Official testing is an average of positive and negative tests, for exactly the reason you mention. They also make a note of wind conditions on the day, and won't (or shouldn't) test if it's above a certain wind speed, I believe. I think they did three cycles ([positive + negative] x 3) of the test when they did ours. With the house depressurised, even small leaks were very obvious. We got just under Passivhaus airtightness on our first run (despite the front door not actually being closed properly!) They depressurised it after the last run and let us go around for a few minutes looking for any leaks. The biggest was clearly around our large slider, as expected. There were also a couple of pin-pricks in the airtightness tape due to misplaced staples near windows. Unfortunately, for a decent sized house you'll spend a lot of time going around all the interfaces for relatively small gains, and it's unlikely a tester is going to hang around for that unless you're paying. Link to comment Share on other sites More sharing options...
Crofter Posted January 16, 2017 Author Share Posted January 16, 2017 Thanks all. To be honest I'm wondering if I should bother. The drafts were pretty obvious the last breezy day we had. I think that as I block up more of them, the airflow through the remaining ones becomes stronger- does that sound right? It's a lot easier to wait for a breezy day than it is to rig up a DIY test kit. Also, whilst numbers would be nice to have, I don't think they would change anything. So whether I am getting 5ach or 2 (or however it is measured) I will still be installing a MVHR. Link to comment Share on other sites More sharing options...
gravelld Posted January 16, 2017 Share Posted January 16, 2017 @CrofterI've often had a similar theory about sealing up making other issues more obvious, I think the problem with that is you're still at the mercy of "natural" pressure differences (i.e. the wind). EDIT this editor is driving me mental, is there a plain text one? I think it's ideal if you can rig up a test system. What I would say is that you can leave the actual measurement until later. Link to comment Share on other sites More sharing options...
jack Posted January 16, 2017 Share Posted January 16, 2017 25 minutes ago, Crofter said: The drafts were pretty obvious the last breezy day we had. I think that as I block up more of them, the airflow through the remaining ones becomes stronger- does that sound right? Not sure about that. Take the end case of there only being one small hole left. It'll take a lot of fast pressure changes between inside and outside for much air to be driven through it. I'd guess that the more of the larger holes you block off, the harder it will be to detect air movement through the remaining smaller ones. Link to comment Share on other sites More sharing options...
gravelld Posted January 16, 2017 Share Posted January 16, 2017 Good point. Probably the reason my theory never took hold. I think forced air movement is the obvious way to go. One other interesting topic on this that comes to mind is that if you have a DIY rig you can move it around the house, sealing it against internal doors (assuming a hard floor to seal against). Might help pinpoint troublesome rooms. Link to comment Share on other sites More sharing options...
ProDave Posted January 16, 2017 Share Posted January 16, 2017 3 hours ago, PeterW said: The reason for a negative pressure testing is that air infiltration can come via the cavity so a positive pressure test would not show where the leaks were going to. The correct test measurement method looks at the power input to the fan and maps that against the pressure in the building - the harder the fan has to work (ie the increase in current) the more air tight the building. I see, so in an official test, the fan speed is controlled in a closed loop system to maintain the pressure differential, and the amount of power needed to maintain that measured the air tightness. Link to comment Share on other sites More sharing options...
PeterW Posted January 16, 2017 Share Posted January 16, 2017 3 minutes ago, ProDave said: I see, so in an official test, the fan speed is controlled in a closed loop system to maintain the pressure differential, and the amount of power needed to maintain that measured the air tightness. Yes that's correct - laptop to a controller that is monitoring the voltage and current to the fan. Last one I saw the fan had calibration stickers on it - not sure who from though. Fan was mounted into a metal frame that fitted a doorway and the gap between had some sort of rubberised nylon fabric to allow it to flex and "suck" back into the building. Link to comment Share on other sites More sharing options...
SteamyTea Posted January 16, 2017 Share Posted January 16, 2017 How easy would it be to make a speed controller that can be set by pressure sensor data i.e. one inside, one outside. Ideally it would work from a laptop that can also log the pressure differences and voltage and current to the motor. Link to comment Share on other sites More sharing options...
MikeSharp01 Posted January 16, 2017 Share Posted January 16, 2017 15 minutes ago, SteamyTea said: How easy would it be to make a speed controller that can be set by pressure sensor data i.e. one inside, one outside. Ideally it would work from a laptop that can also log the pressure differences and voltage and current to the motor. Yes that is an idea, some thoughts from me - needs refining I suspect. Just get a USB / blue tooth controlled motor inverter that will set the speed and provide all the current / power feedback you will need. Then two pressure transducers in and out, Once the pressure difference is reached back off the power (speed) and until it holds steady then measure the airfow. Thinking about it you might be able to calibrate it by running the fan into a sealed, guaranteed, box - will probably need to be quite large or turbulence might be a problem, then measure the pressure difference and get the fan power back to stable desired pressure difference then take the power reading. If the house is sealed once the pressure difference is reached the difference from the power reading taken above will be proportional to the leak area. If you drill holes in the sealed box you can see just how big your leaks are by matching the power readings for known hole sizes (areas). (PVT so keep the temperature stable.) Link to comment Share on other sites More sharing options...
Guest Alphonsox Posted January 16, 2017 Share Posted January 16, 2017 (edited) Here's a quick photo of the fan installed in the back door of the build. Some more info available on the manufacturers pages http://retrotec.com/products/blower-door-systems?field_market=35 Edited December 11, 2018 by Alphonsox Image deleted due to copyright issues Link to comment Share on other sites More sharing options...
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