Handbook of Radon.
56. The role of heating systems in determining radon levels.
There can be strong interactions between heating system design and operation and average indoor radon levels. The effect can be most marked in mechanically ventilated buildings and has been well demonstrated in schools in the USA.
In the UK, the most pronounced interactions have been in houses where old fashioned open fires or 'Baxi' type fires are used on a regular basis. The common factor is substantial suction on the room as a consequence of the large air flow rate up chimneys.
Often, not all the house will be affected by the suction because internal doors may be kept shut (to stop the noticeable draught round the door when the fire is burning!) and in these cases large room-to-room differences in average indoor radon level may be experienced. Short term levels room to room may be different by a factor of 50 or even 100.
In mechanically ventilated buildings, radon levels can be equilibrated by the air mixing that may be an inherent feature of the system design. However, if different rooms run at different pressures some may be pressurised and some depressurised relative to outdoors, and with (consequently) large differences in average indoor radon levels, and these may be reasonably stable in time.
Choice of different monitoring periods and of rooms selected for monitoring may therefore produce large differences in measured average radon levels.
Also, it is entirely possible for subsequent changes in the operation of the heating or air conditioning systems (deliberate or as a result of failures) to induce large changes. This is an example of buildings not having fixed indoor radon levels.
A debate is underway in the USA as to the most appropriate response when mechanically ventilated buildings are found to be affected by radon. Similar considerations apply to some UK houses served by underfloor-ducted warm air heating. Much can depend upon system pressures and whether the ducts are well sealed. The author may be consulted for further details.
Some experts contend that radon removal systems should be installed (almost irrespective of cost) whilst others, supported by the author, argue that faults and imbalances in H&V (heating and ventilation) systems should be remedied and the buildings reassessed for radon. These measurements should be made only during occupied hours if appropriate, before classifying the rooms as requiring conventional radon systems.
This approach is logical since many buildings that are measured as low in radon may be driven to higher levels at some future date by faults in their H&V systems. The logical cure is simply to return the H&V to its previous state, and which, in the case of some faults, may pay dividends in terms of improved indoor air quality (if not energy consumption).
A parallel argument is that smokers should reduce their radon risks by giving up smoking rather than continue with a dangerous habit whilst expending possibly large sums of money on removing a relatively minor hazard.
KEY FACTS:
Heating system design and operation may much affect indoor radon levels throughout mechanically ventilated buildings. Systems may tend to equalise indoor levels, or to exacerbate problems in a few rooms. Simple diagnosis can resolve any uncertainty.
Large effects may occur locally in naturally ventilated houses owing to operation of open fires.
Heating system design or operation may determine whether a building is classified as above or below the so-called action level, and depending upon the room selected for measurement.