Moisture management, and the death of an aussie icon

The gasps from the audience were audible! You’d have thought I’d just shot Bambi, ruined the weekend, or revealed that I don’t see the point of cricket.

What had I done? All I said was:

This winter, in Melbourne, if it’s cold and wet and your windows are closed, don’t hang laundry around your house to dry

I’ve been telling my home comfort and energy clients this for years, and yes, I’ve heard some interesting responses! I’ve seen thousands of reactions to posts on this topic online at My Efficient Electric Home. But to see a whole face-to-face community audience react so vocally… well… time to recite the entire story.

I invite you to read this, especially if:

• you have draught-proofed your home or are thinking of doing so;
• someone in your household experiences asthma, dust mite allergies, or reacts to mould;
• you have found mould damage on leather goods or other materials hidden away in damp closets and wardrobes;
• you see other signs of mould or excessive moisture such as water condensation on cold windows.

Managing winter-time moisture in your home is a key to health and comfort

In winter, many Australian homes are too damp. The air in our homes may contain too much water, moisture, humidity, condensation, call it what you will.

For best health outcomes, aim to maintain a relative humidity (RH) level no higher than 50 per cent for at least some part of the week.

In many homes (including my own in bayside Melbourne), getting down to 50 per cent RH is a challenge, especially in our generally unheated master bedroom. This happens without us making things worse by hanging clothes around the house to dry.

Health impacts relating to mould, dust mites, bacteria, viruses, and asthma can be lessened if home RH is not seasonally up at 80 per cent or 70 per cent but at times falls to 50 per cent.

Mould can form as black spots in places where we can see it, and also in places where we can’t see it, such as in our walls or above ceilings. Hidden mould can grow especially in homes that have not been draught-proofed and have air-leakage pathways through the plaster. Mould spores released in hidden spaces can work their way back into the air we breathe.

The humidity “sweet spot” at around 50 per cent RH is illustrated in the classic “Sterling” chart, published in 1985, with further interpretation of that chart provided here.

What causes winter humidity to be too high in Australian homes?

In our Australian homes, where does moisture come from and why can it accumulate to unhealthily-high levels? Here are nine reasons. There may be even more.

1. People and pets breathing, fish tanks and houseplants add moisture to a home, all of which may be unavoidable if these are parts of our desired lifestyle. Two people sleeping in a bedroom overnight can breathe out two cups of water (one-half litre), which you might find in the morning condensed on cold single-glazed windows.

2. The weather has been wet and rainy, and even exceptionally so (e.g. this autumn in Melbourne), and the home’s building fabric or human operators aren’t the best at keeping moisture out of the house.

3. A house may be situated in a damp micro-climate, on the rainy side of the Dandenong Ranges, in a gully over what was once a stream bed or carved back into a muddy hillside; and again the home’s building fabric and human operation isn’t set up to resist this challenge.

4. Drainage around the house may be inadequate, or the roof or windows may leak. A property may experience flooding.

5. Windows aren’t being opened optimally to provide “fresh” air and to purge excess moisture from the house. However, note that items 2,3, and 4 above might mean that opening windows or even running a mechanical ventilation system (see below) isn’t going to move much moisture out anyway. 

6. Extraction fans in the kitchen and bathrooms aren’t performing or being operated in an optimal way.

7. A house has been draught-proofed, but moisture isn’t being managed. To reduce energy bills, many of us are draught-proofing our homes by sealing chimneys, ceiling vents, wall vents, gaps under doors, above fridges, around window architraves, etc. However, when draught-proofing we must pay equal attention to the “active ventilation” needed to purge moisture and other contaminants.

8. A home is being under-heated as the householder tries to limit energy bills. Heating a room sufficiently, on its own, won’t cause moisture to leave a house, but you can chase moisture from a particularly cold and damp room into a less damp zone by using a heater (or perhaps a fan).

9. Laundry, including wet bathroom towels, has been left hanging around the house to dry; or, is being dried with a classic “vented” clothes dryer that is not vented to the outdoors.

How to monitor a home’s humidity level for $20

How can one easily monitor home humidity? Is your bedroom running at a high 70 per cent RH, or is everything fine and dandy down at the ideal 40 per cent RH?

I purchased a combination temperature / RH monitor off the internet for $20. It works and it’s something I now demonstrate with my clients. More sophisticated devices are also available. It arrived in the post after just one day. Very quickly I confirmed how high is the RH in our master bedroom, ranging up to 70 per cent. Are dust mites a reason I often wake up with headaches?

Even without an electronic RH monitor you may have already seen clues that your household humidity is too high, such as water condensing on cold single-glazed windows, or damp or mouldy spots on walls, ceilings, or in closets.

How to move moisture out of your house

Since we are constantly adding moisture to a house, how can we make sure it leaves? Referring back to the list of how moisture can get into a house leads to ideas of what we can do about it.
Wipe up any condensed water that appears on windows with a chamois cloth or in more extreme situations with a window-cleaner’s electric vacuum. Moisture left on windows can result in black mould spots appearing on the glass, as well as aesthetic and structural damage to wooden window frames or architraves.

Open a window if outdoors it’s sunny and less humid. Open blinds to get the sun’s passive solar heat into a room. Open interior doors, to connect those musty teenage bedrooms with the rest of the house.

Actively heat a damp room if necessary. For an hour or so it can make sense to open a bedroom window while the heater is left running, if this is the only way to get excess moisture out of the house. And as I wrote in “7 Things People Don’t Know About Their Homes”,  use a reverse-cycle air conditioner for the cheapest heat.

Run kitchen and bathroom extraction fans purposefully, with nearby windows cracked open to help the fan do its job. Over the shower, consider a “Showerdome”.

What won’t work is to expect a small container of desiccant (e.g. “DampRid”) to remove more than a small amount of moisture before you throw the chemical away. This limitation means those products may best be used in closets or other small spaces.

And if your windows are all closed because the weather is cold and wet, but you’ve had to wash a load of laundry, don’t hang it around your lounge room to dry.

So how am I meant to dry my clothes?

So how to dry laundry? By all means, take advantage of solar energy and hang clothes outside to dry when the weather is suitable. But it isn’t always. So then what?

No, I’m not suggesting you use an old technology “vented” electric dryer. Those things use a lot of electricity whilst blowing hot moist air into your face and into your laundry room or closet (unless they are ducted to the outdoors). And then you must run an extraction fan or open a window to get that moisture out of the house. I understand why my clients who have held on to these relics claim to “hardly ever use it”.

Here are three better options.

1. The miraculous heat-pump-condensing clothes dryer

It was only about six years ago that I learned of the existence of seven-to-ten energy star-rated heat-pump-condensing clothes dryers. And judging by what’s on display at the whitegoods shops, these days it’s mostly what they sell.

A heat-pump dryer uses as little as one-quarter of the electricity consumed by the one-to-two star “vented” clothes dryers. Heat pump dryers condense nearly all the moisture into a bin from where it can be put down the drain. The valuable heat of water condensation is recovered and recycled by the heat pump to further dry the clothes. Very little energy is wasted in this process.

Here’s a video of me dumping the water down the drain. Note the two litres of water that did not end up contaminating the air of our house.

2. Use a desiccant dehumidifier

We are using a desiccant-type dehumidifier (recommended in cooler climates for winter service versus a refrigerative-type) to dry our bedroom. If we didn’t have a heat-pump condensing clothes dryer, we could hang our laundry in a small room with the dehumidifier running. This would ensure the water from our clothes is captured by the dehumidifier and then we’d pour that water down the drain.

3. A designated laundry-drying room

If you won’t be buying any new equipment nor using a clothes dryer or dehumidifier, the best you may be able to do is to designate a spare room as the laundry-drying room. Isolate this room from the rest of the house, open windows, and now you’re not hanging laundry around the house with windows closed. Rather you are doing it in one room with windows open. But caution: if this room is connected to a ducted heating system you could be throwing costly heat out the window.

Why a mechanical heat recovery ventilation (MHRV) system might not solve moisture problems

A growing number of Australian homes (in the cooler climates) are being fitted with mechanical heat-recovery ventilation (MHRV) systems, including any house built to the European passivhaus standard.

If the air outside of a home is dry while the air inside is damp, an MHRV will help to dry a home. But the weather isn’t always dry and therefore MHRV’s can’t be expected to always solve moisture problems.

This autumn in Victoria, the air drawn in by an MHRV often contained just as much moisture (absolute humidity measured in grams of water per cubic meter of air) as the air the MHRV blew out of the house. During such damp conditions, the MHRV might have no impact on the level of moisture or indeed could even increase humidity throughout a home or in a bedroom.