At the moment it is de rigeur to try to seal off every last little crack in the envelope of one’s house in order to save energy. The message seems to be – if you don’t draught proof your house you can’t be serious about managing your carbon footprint.
This is fine as it goes, but there is another side to this issue: you also have to breathe! Almost every day I seem to come across calls in the energy media for everyone to seal their houses, but rarely do these pleas mention the need to maintain adequate airflows.
About two years ago, I began to be swept up in this trend. I did some very basic gap sealing around doors and closed off some unused vents in our house. I planned to progressively seal up the house once I had settled on our heating and cooling regimes. However, earlier this year I started to come across articles about monitoring indoor CO2 levels as a way to track indoor air quality. I became intrigued and decided not to do any further draught proofing until I’d carried out my own monitoring.
Why should we be interested in indoor CO2 levels?
A quick Google will reveal that high CO2 levels can be hazardous (and ultimately lethal) – see this US Bureau of Land Management paper for example. At high concentrations CO2 is both toxic and an asphyxiant (ie it will displace oxygen in the air) but there seems to some expert debate about the relative importance of these two effects. More importantly for this paper, research shows that for humans, task performance begins to degrade when CO2 levels reach about 1,000ppm.
The literature suggests you are not likely to find toxic levels of CO2 in your house unless you live near an erupting volcano or near certain mining/gas operations. By the same token, my monitoring suggests that even in a ‘normal home’ you may well have indoor CO2 levels that are high enough to affect your judgement and make you drowsy.
CO2 is important in the context of indoor air quality, since it is commonly the only indoor air pollutant that is continuously being emitted by the occupants of a room (via breathing). In an occupied room, if the ventilation is inadequate the CO2 levels build up until some, or all, of the occupants leave or fresh air is introduced (eg by opening a window or turning on an extractor fan).
Monitoring CO2 levels in our house
I bought a CO2 monitor on Ebay – this is shown in Figure 1. It is certainly not a laboratory grade piece of equipment but it seems fine for my purposes. When I began monitoring I was very surprised by the results.
I had imagined that our crudely draught proofed house would have good air quality given how many paths there are for air to enter and leave. In particular, at this time of the year, when we open our windows, I had thought that our CO2 levels wouldn’t be too far above the outside levels. I was wrong! Figure 2 shows a plot of one night’s CO2 datalogging in our main bedroom with windows open – the CO2 levels gradually built up over the night and, for a time, the levels exceeded the recommended acceptable level of 1,000ppm.
While I have only been monitoring for a week or so I am confident the data in Figure 2 is not an anomaly – it appears to be the norm. I am now quite fearful about what the levels will be in winter if we follow our usual practice and close all windows.
Responding to the high CO2 levels
My initial reaction to my monitoring results has been to start undoing our draught proofing. I have unblocked some of the vents in our house and will progressively open up the house to see if we can keep our CO2 levels consistently below 1,000ppm throughout the year. In the end, if this is not achievable we may have to install a mechanical ventilation system.
To some, un-draught proofing a house will undoubtedly be seen as the wrong response. Indeed, if you have a house that is heated by some form of ‘warm air’ heating opening up air gaps could have a significant detrimental impact on energy use. However, this is not such a problem for us as we are heating our house with Far Infrared (FIR) panels. FIR heats people and objects, not air, and therefore our prime heating effect comes from direct radiant heat and not from secondary heat contained in warm air. Given this, I don’t expect our energy use will be significantly affected if we open up air gaps.
Recommendations and further reading
Don’t make my mistake. Don’t assume that just because you have a leaky house you have good indoor air quality. If you are planning to draught proof your house I would strongly recommend that you monitor your indoor air quality and work out how you are going to ensure good airflows.
I have prepared a more detailed paper on my CO2 monitoring which the reader may find useful.
This post was published on December 20, 2016 1:16 pm
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Interesting. Obviously "balance" is important, especially in the Canberra environment. There may be a market opportunity for a local distributor of Venmar equipment...
Ventilation - as suggested here - is a significant issue, especially in a well built home. The conventional 'fall back' position is to open windows. However, in cold weather and hot weather, this is not a sound idea.
The designers of the "passivhaus" now popular in Europe get around this by using 'heat recovery' ventilation whereby stale air is pumped out as fresh air is drawn in and heat exchange occurs so that the house temperature in not much effected by the ventilation process.
The Australian environment is not as aggressively effected by external weather so although heat recovery units may be used, something simpler could fit the bill.
I use an attached greenhouse. Fresh, oxygenated air is drawn into the house from the greenhouse and this forces stale air out through standard vents (kitchen and bathroom) without any real change in temperature.
An option if you need fresh air, rather than turning your house into a sieve, is to open a window. Using windows means the occupant is in control of the ventilation / home performance, rather than leaving it to the vagaries of outdoor wind speed, etc.
I have a pretty tight Melbourne house that is a reasonable good energy performer, and to admit fresh air when needed, we open windows.
One finds a lot of vents and gaps in existing homes and some of these date back to the times of gas lights, regular use of fireplaces, dodgy gas-burning equipment, or damp issues. Fortunately in some homes, times have changed and efficiency and comfort have improved from a century ago...
The problem is Tim that we are getting marginal air quality even with windows open (admittedly only a small way). Ultimately we may have to install some form of mechanical ventilation. My main concern at the moment is that, based on my monitoring, many people are unwittingly exposing themselves to potential health hazards. I think we need to include many more caveats about ventilation in our draft proofing messages.
Very useful article Dave. Thanks for the data.
About 1 year ago I saw a research paper logging CO2 levels in automobiles when the 'recirculate' button was activated. Those researchers also found that CO2 levels would easily climb past 1000 ppm. Until I read that article I routinely drove with recirculate activated to minimize exhaust fumes, especially the high PM 2.5 diesels. Now I try to switch back and forth.
It's a bit odd that such a basic safety concern has received little attention...
Dave, a very eye opening article. I was astounded to see over 1100ppm in your bedroom and with the windows open. I note that start levels were over 500ppm which is of course more than what should be registered in the outside air. Do you live next to a busy road?
My other thought was that the meter you purchased is way out of calibration, perhaps you should get a certified company with a lab quality meter to come in to confirm or deny your results. Or go to a University lab and compare the two readings.
I also was very surprised at the readings in our bedroom. I'm not sure whether you have read my monitoring report but you'll see that I've worried a lot about the accuracy question. At this point I think my monitor is reasonably accurate - it calibrates well (within the accuracy of the meter) with 400ppm whenever I measure outside; and indoors it shows totally rational behaviour ie when CO2 levels go up or down (more or less people in a room) it behaves entirely as I would expect. Having said that, I would love to see, and compare, my readings with the CO2 levels others are measuring within bedrooms.
I have looked at and dismissed any influence from road traffic (I thought I might find a correlation but it doesn't seem to be there).
Dave, I think your article is overly alarmist and potentially detrimental to our efforts to reduce our emissions. The literature I found talks about a limit of 5,000 ppm.
If you look in my monitoring report (cited in the article) I give two references where the researches actually recommend an upper limit of 600ppm. Nearly all the references I found (and there's quite a lot) recommend 1,000ppm.
What's the source?
Did you check your heating system?
1) Does your heating system got an outside air intake?
2) is your heating flue ( exhaust ) properly sealed?
3) Do you have an attached garage? When did you come home? Do you have an air leak from the garage?
Some good ideas but I don't think they apply in our case.
In winter we are heating with Far Infrared and have disconnected from the gas network. At this time of year (the readings were taken in November) we don't use any heating.
We do have an attached garage but no car was used for about six hours before I began monitoring. If the high readings were caused by residual CO2 in our garage leaking into our bedroom I would expect the levels to reduce, not increase, overnight. The readings in the graph were not an isolated event - it appears to be quite typical. When I have carried out datalogging in our children's bedrooms I've been getting max readings of about 600ppm - they leave their bedroom doors open; we close ours. (Their bedrooms are closer to the garage than our bedroom.)
I think all my readings are totally consistent with the CO2 being emitted by our breathing. Even with windows open (albeit only a small way), the rate of CO2 injected by our breathing is exceeding the ventilation capacity of the room.
I give more details in my monitoring report which is cited in the article.
Dunno if there is some confusion between carbon dioxide and carbon monoxide going on here?
Mechanical ventilation makes much more sense than using miscellaneous leaks to provide ventilation. Air that leaks in through walls or crawl spaces is not likely to be truly fresh. A mechanical ventilation system brings in fresh, filtered outside air.
Are we missing the game here?
Sealing has its place in the building, but obsessing with this may miss the other important areas, such as Insulation, passive solar design and thermal mass.
Double glazing is another problem area. While retailers would love to sell you (an expensive) double glazing option, It only makes sense when the windows are the dominant thermal issue. Up to that point, other matters, like leaks and insulation are more important.
Move to Europe or Canada and many houses are totally leak sealed, but don't have stale or rancid air because of heat recovery ventilation systems. In Australia, we are fortunate that we are not dealing with 50+ deg.c temperature differences and can do a lot of our air exchange with opening windows.
I suspect that, in order to achieve a 9+star rating, all of these have to be done within a building design that accomodates them.
Any energy efficiency efforts need to be tailored to the local climate. But there are few places where single glazing is appropriate. A single pane of glass has an R value of less than 1. They are appropriate only in climates with minimal heating and cooling loads. The value of adequate insulation is seriously compromised when low efficiency windows are used. There is no point in installing R 20 walls with R 1 or R 2 windows. Moreover, double or triple pane windows provide the occupants much more comfortable surroundings, since, if properly installed, they allow one to sit next to the windows without feeling cold.
I live in Maine, which gets pretty cold. My efficient triple pane windows (R 10) help keep us warm and comfortable, as does ample insulation (R 42 walls, R 70 roof), good air sealing and mechanical ventilation.
Houses should be designed and built as integrated systems, with attention to air sealing, insulation, ventilation and aesthetics.
The R value of windows is so bad, only a tipple pane window makes any sense at all. For All of Canada, and most of America.
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