This investigation tried to answer the question of a possible dependency of the occurrence of mites in carpeting, mattresses and upholstery from the type of the heating systems. Radiator and under floor-heating system. Radiator and under floor heating were compared.

Materials and methods

21 households were investigated in a randomized trial. 10 dwellings had under floor heating, 11 had radiators. Upholstery and carpeting in the living room, mattresses and carpeting in the bedrooms were inspected for moulds and mites in all 21 dwellings. Under consideration of the above mentioned seasonal pattern specimen were taken in February, may, august, and November of the year 1989. The complete surface of each object was vacuumed for a standardized time of 2 min/sqm. The dust filters were stored below 6 degrees Celsius up to 3 days. The dust filters were weighed for a quantitative analysis. The content of living and dead mites was determined by the floatation method (1) and microscopic inspection. Stout mites with compete bodies (tentacels and legs) were called "living". Mites without these features were called "dead". All determinations were done three-fold. 

The mould analysis to determine the colony forming units (CFU) was done by the dilution method (2). This determination was also done three fold. Malt agar plates with an addition of sugar were used as culture matrixes to provide conditions equivalent to those of a relative humidity of 95%. After inoculation the plate were incubated at 25 degrees Celsius for 1 week and then analyzed quantitatively and qualitatively.

Results

The mean number per square meter of living and dead mites (dermatophagoides pternossinus and d. farinae) and of the most common moulds (caldosporium, Aspergillus and Penicillium) were determined. Fig.1 shows the number of living mites in carpeting, In February and November, the number of living and dead mites in radiator heated dwellings is significantly higher than in those with under floor heating. The mean number of living and dead mutes in radiator heated dwellings increases strongly in spring and summer until November. The corresponding numbers in dwellings under floor heatings is significantly lower. There is only a slight increase in the number of living mites in summer. The reducing effect of under floor heating on the growth of mites and moulds can also be found in upholstery and mattresses. In February, we found 624 mites/sqm in upholstery in radiator heating dwellings, while only 53 mites/sqm in dwellings with under floor heating. The number for mattresses are 470 and 34 mites/sqm. In August, we found significantly more living mites in upholstery and mattresses in radiator heated dwellings, while in November the number of dead mites in upholstery in dwellings with under floors heating systems was significantly higher then in radiator heated dwellings. 

Discussion

Under floor heating in an indoor environment provides climatic conditions that reduce the growth of mites and moulds efficiently. Especially in the carpeting of living rooms almost no mites could be found. This effect was not as stronf in the bedrooms, which is most likely related to the fact that these rooms are not as consequently heated. The big heating surface of an under floor heating provides a regular and steady heat ditribution. 

In addition, the coldest area of the room is no longer the floor as with radiator heating- and subsequently the carpeting has a lower relative air humidity. Because with an under floor heating the temperature gradient declines from the floor upwards- in contrast to a radiator heating- and subsequently the carpeting has a lower realtive air humidity. Because with an under floor heating the temperature gradient declines from the floor upwards- in contrast to a radiator hearing- this is also of benefit for upholstery and mattresses. This was most evident in our February investigations.

Under floor heating in an indoor environment provides climatic conditions that do not allow moulds to grow in house dust. This is especially true for the Aspergillus group, which lives in a symbiosis with house dust mites (1). Cladosporium, a typical outdoor air mould (3), has its climax in summer and can then be found in similar concentrations in radiator heated and under floor heated dwellings. This mould reaches the indoor space by air through open windows in summer. At first, one is surprised that also in February and may the number of mites in carpeting of radiator heated dwellings, although the heating usually is not used in summer. This is most likely related to the fact that dry dust is much easier vacuumed from the floor, which leaves less nutritive materials to the mites and that for this and other reasons the starting population at the beginning of the generating season is smaller. 

Conclusions

The limiting factor "Under floor heating" is an "active preventive factor" in as far as it keeps the allergen producers on a low level throughout the whole year. The consequence is a lower allergen production in dwellings with under floor heating than in radiator heated dwellings. Importantly enough to be mentioned especially for the allergic person is that with the regular and steady heating of the under floor heating there is significantly less airflow and turbulences. Subsequently there are much less allergens in the air. 

In conclusion, the described results strongly indicate that under floor heating efficiently reduces the growth of mites and moulds in the indoor environment and as a consequence improves the life quality of the allergic person.
 
 

(1) Bronswijk J.E.M.H. (1981) "House Dust Biology"
(2) Lustgraaf B. van de (1978) "Ecological Relationship between Microorganisms and house-dust mite"
(3) Wilken-Jensen K., S.Gravesen (1984) "Atlas of Moulds in Europe Causing Respiratory Allergies"