Making your own PM2.5 dust-free room in Chiang Mai: what to do first, and which jobs to leave to a technician

Every year, once February arrives, dust-free rooms and clean-air rooms become a topic in Chiang Mai again. I understand that this is when many households want at least one space where they can breathe freely. Various public bodies open clean-air rooms where people can shelter from the dust, which is very useful for those with no other option. But most people spend their time at home, so the more useful question is how to turn one room in your own home into your own clean-air room.

What I go into below is the part you can actually do yourself in your own room: choosing the right room, sealing gaps in order of importance, choosing the size of air purifier, and the points where a technician should step in.

What a dust-free room is, and what it is not

The Department of Health's guidance on dust-free rooms sets out a simple principle: make the room as airtight as you reasonably can to reduce the dust coming in from outside, then deal with the dust still inside using an air filter or by circulating the air within the closed room. The heart of the idea is the order: seal first, then filter.

What I see very often is a customer who has bought an air purifier costing several thousand baht and put it in a room where the windows do not close properly and there is a gap of about two centimetres under the door. The purifier runs flat out all the time but the dust reading in the room does not drop, because new dust flows in at roughly the same rate as the machine filters it out. If part of the budget meant for a large air purifier goes on silicone sealant and door draught strips first, you get far better value.

Which room to turn into a dust-free room

I recommend starting with a single room rather than the whole house, and in most cases the answer is the bedroom, because it is the room you stay in for the longest stretch each day and breathe in most steadily. If you have several rooms to choose from, use these points to help you decide.

• The smallest room that is still comfortable to use, because a small room is easier to seal and an air purifier can cover it more thoroughly.
• A room with few windows, and windows that close tightly, not louvre windows, which are hard to seal.
• A room not next to the kitchen, because smoke and cooking fumes are a major source of indoor dust in the home.
• A room that does not face directly onto a main road or a car park.
• A room that already has an aircon installed, so you do not have to choose between opening the window and putting up with the heat.
• A room without carpets and lots of stored items, because these trap dust that can be stirred back up at any time.

If you live in a condo or a dormitory room in Chiang Mai, you have an advantage over a detached house, because the rooms are usually small, seal better and share walls with other rooms instead of facing outside air on every side. The points to pay special attention to in this kind of room are the gap around the front door, the bathroom extractor fan opening and the aircon pipe hole.

Sealing the gaps, one point at a time in order of importance

The way I most often find leaks is to do it in daylight: switch off the lights in the room, close all the doors and windows, and look for light coming in. Anywhere light can get through, dust can get through too. Another way is to use a thin wisp of smoke and watch which way it drifts, which shows the direction of the leaking air clearly.

1. 1

   The gap under the door and around the door frame

   This is the biggest leak in most of the rooms I have looked at. Use a draught strip fitted to the bottom of the door, or a free-standing draught stopper. Around the frame, use self-adhesive weather strip so the door closes flush.

2. 2

   The joint between the window frame and the wall

   Old windows often have small, hard-to-spot cracks between the frame and the wall, which you can seal with silicone. For the joints between the parts of the window that open and close, use self-adhesive weather strip instead.

3. 3

   The aircon pipe hole through the wall

   This is the most overlooked point, and it is a hole that goes straight through to the outside. Check the wall below or behind the indoor unit for any gap around the pipes. If it was plugged with putty or foam that has dried out and gone brittle, it should be sealed again.

4. 4

   Extractor fan openings and vents above the door

   Many rooms have louvred vents above the door or near the ceiling. During the smoke haze season, cover them temporarily with a sheet of acrylic or thick plastic taped in place, and open them again when the season is over.

5. 5

   Gaps in the ceiling and service hatches

   Ceilings with an access panel for repairs often do not close flush, and the space above the ceiling connects to the roof void, where a lot of dust collects. During the smoke haze season, tape round the edges with cloth tape.

6. 6

   Sockets and switch boxes on outside walls

   These are small holes but there are many of them. Use sealed socket covers, or cover unused sockets with blank plates. This can be done later; it is not as urgent as the first four points.

7. 7

   Make the entrance double if you can

   If the room opens straight to the outside of the house, a heavy curtain or a second door will cut down a fair amount of the dust that blows in with you each time the door is opened and closed.

Choosing an air purifier to suit the room size

Once the room is sealed, the air purifier deals with the dust that is left. Choosing one is not complicated. First, it must use a HEPA filter, because that is the part that actually traps fine particles. Second, look at the coverage area the manufacturer states and compare it with the real size of your room.

My further advice is not to pick a model whose stated coverage exactly matches your room size, but to go one level up. The figure on the box comes from testing in a fully sealed room to a standard, while a real room has leaks, people coming and going, and a higher ceiling than the test room. With some margin, you can run the purifier at low speed, which is quieter and uses less power than running a small unit at full power all night.

• Place the unit in the middle of the room or near where you sleep, not tight against a wall or under furniture, where it cannot draw air from the whole room.
• Leave space around the unit so air can flow in and out freely, especially on the intake side.
• Replace or clean the pre-filter as the manual says, because in the smoke haze season it clogs much faster than usual.
• Do not wash a HEPA filter with water unless the manual says it is washable, because the filter material is permanently damaged.
• Keep the room door closed the whole time the unit is running, otherwise you are using a one-room purifier to clean the air of the whole house.

The role the aircon plays in a dust-free room

It is worth knowing that an aircon is not a dust filter. The filter that comes with the unit is designed to catch coarse dust to protect the coil, not to filter PM2.5. But the aircon is an essential part of a dust-free room, for two reasons.

First, the aircon is what lets you stay in a sealed room. In Chiang Mai from March to April, a sealed dust-free room without an aircon gets too hot to stay in for long. Sooner or later the window gets opened, and all the work of sealing the gaps is wasted. The aircon is what makes the plan workable for the whole season.

Second, the aircon helps circulate the air inside the closed room, so air passes through the purifier more thoroughly than in a room where the air is completely still. But there is an important condition: the coil must be clean. If mould has built up on the coil, what you get from sealing the room is a closed room with mould spores circulating in it, which is no better than the dust outside.

The jobs a technician should do

Most of the work of making a dust-free room you can do yourself in a day without hiring anyone. But there are five points directly connected to the aircon that I recommend leaving to a technician.

Mistakes that stop a dust-free room from working

• Buying an air purifier before sealing the room, so the unit works hard all the time but the dust reading does not drop.
• Leaving the room door open while the purifier runs, which means using a one-room unit to clean the air of the whole house.
• Sweeping instead of wiping the floor, because sweeping stirs dust that has settled back up into the air.
• Cooking, burning incense or smoking in the part of the house connected to that room, which becomes a bigger source of dust than the outside air.
• Not washing the purifier's pre-filter during the smoke haze season, when it clogs much faster than in other seasons.
• Keeping lots of rugs, soft toys and thick blankets in the room, because they hold dust that is stirred up every time they are moved.
• Leaving the aircon in that room uncleaned all year, even though it is the unit circulating the air you breathe all night.

What to do, in order, if you start today

1. 1Choose one room first, usually the bedroom; do not do the whole house yet.
2. 2Switch off the lights in daylight, look for leaks where light gets in, and write every one down.
3. 3Seal the gap under the door and around the frame first, because it leaks the most and costs the least.
4. 4Then move on to the windows, vents and the aircon pipe hole.
5. 5Have a technician clean the aircon in that room before the season starts; if there is a musty smell, choose a strip-down clean.
6. 6Only then choose a purifier to suit the room size, and place it in the middle of the room or near where you sleep.
7. 7Adjust a few habits: keep the door closed at all times, wipe the floor instead of sweeping it, and wash the aircon filters yourself every 2 weeks as manufacturers recommend, and no longer than 4 weeks during the smoke haze season.

Summary

• The principle is seal first, then filter. Seal the room before you invest in a purifier.
• Starting with one room is enough, and for most homes that room is the bedroom.
• The biggest leak is the gap under the door, followed by the window frames and the aircon pipe hole.
• Choose a purifier rated for more than the real room size, so it can run all night at a quieter low speed.
• An aircon does not filter PM2.5, but it is what lets you stay in a sealed room all season.
• The coil must be clean, otherwise a sealed room becomes a room that circulates mould spores for you to breathe.