In this question on an alternative way of heating a comment was made that

There are significant potential health risks with lowering a house to 16 degrees C

What kind of potential health risks are we talking about here? And under which conditions would they occur?

To make this question a bit more concrete: in our home we tend to only heat the living room, kitchen and bathroom. The bed rooms, hallway and toilet are hardly ever heated and temperatures there may drop to 15-16 degrees in winter time (about 60 degrees Fahrenheit). Could this cause health problems?

  • Having been involved in the linked question, I'm curious about this too. My bedroom frequently drops well below 16C at night, while I'm asleep... but I suspect the risks that are indirect ones of having a house that is always cold, such as mould growing, rather than direct ones of low temperatures. Will be interested to see. – Flyto Dec 11 '14 at 9:34

Humidity is a funny thing.

The warmer that air gets, the more water it can hold as vapour. When that air cools down, it can no longer hold as much water vapour; if its humidity was high, then some of that water will condense out onto the coldest surface first. So air that has a healthy, comfortable relative humidity of 50%, when cooled, will have a relative humidity that increases as it cools, without any additional water vapour going into that air.

A room's temperature is also a funny thing

It's common in a lot of energy modelling of dwellings to assume that a room has a temperature. Studies looking at thermal comfort have to be a lot more sophisticated, because things like different radiant temperatures of different surfaces, and a big temperature difference between ankle-height and head height, can be uncomfortable. Most rooms don't have a single temperature - they have lots of different temperatures, clustered around the room's mean temperature. So if a room has a mean temperature of 16°C, there will be spots in that room where the temperature is warmer, and places where it's cooler.

Let's say you've got the bathroom at a nice comfy temperature when you're in it. And the kitchen's a nice comfy temperature when you're there. Maybe the bedroom, when you're not in it, gets down to 16°C. Now here's the thing - air moves around the dwelling. So of that lovely warm air in the bathroom or the kitchen, some of it will find its way through to the bedroom. Now, we put a fair bit of water vapour into the air just by breathing. Add in more water vapour from cooking and bathing, and the relative humidity in the kitchen or bathroom might get pretty high. And after all, relative humidity below 40% or so starts getting uncomfortably dry. Now, as that air gets to the bedroom, it's going to hit some surfaces that are colder than 16°C - 16 was just the average. Windows and window frames, external walls - particularly corners. It will often be the same spots, day after day after day - where there are thermal bridges: spots where heat has an easier route to the cold outdoors; spots that are a degree or three Celsius colder than other places.

Mould and Mites

Now, because those spots I mentioned above will be repeated sites of condensation, then mould will take hold, and flourish. It will keep coming back, again and again. And mould spores are not nice - exacerbating asthma and other respiratory diseases. Additionally, persistent high humidity allows dust mites to flourish, and their waste products also create and exacerbate breathing difficulties: they are "one of the best-documented environmental causes of asthma" (Peat et al 1998). Furthermore, people with Chronic Obstructive Pulmonary Disease (COPD) benefit from additional warming, and suffer in cold rooms (Osman et al 2008)

References and further reading

Oreszczyn T, Ridley I, Hong SH, & Wilkinson P (2006). Mould and winter indoor relative humidity in low income households in England. Indoor Built Environment, 15(2), 125–135. doi:10.1177/1420326X06063051

Preval N, Chapman R, Pierse N, & Howden-Chapman P (2010). Evaluating energy, health and carbon co-benefits from improved domestic space heating: a randomised community trial. Energy Policy, 38(8), 3965–3972. doi:10.1016/j.enpol.2010.03.020

Osman LM, Ayres JG, Garden C, Reglitz K, Lyon J, Douglas JG (2008). Home warmth and health status of COPD patients. The European Journal of Public Health Volume 18, Issue 4, 01 August 2008 p399-405. doi:10.1093/eurpub/ckn015

Peat JK, Dickerson J, Li J (1998). Effects of damp and mould in the home on respiratory health: a review of the literature. Allergy. 1998 Feb;53(2):120-8. doi:10.1111/j.1398-9995.1998.tb03859.x

  • So if I understand you correctly, potential problems are respiratory problems caused by moulds and mites that can thrive due to condensation of warm moist air from warmer rooms flowing to colder rooms. So I guess this would only be a problem for houses that are relatively moist? – THelper Dec 12 '14 at 8:17
  • @THelper prettty much any building that has bathing, cooking and breathing going on in it can be sufficiently moist, unless air-exchange rates are huge. – EnergyNumbers Dec 12 '14 at 9:10

So the problem is NOT low temperataure, but high humidity. High humidity will be a problem at any temperature.

A badly insulated house will encounter problems at lower humidities, since there will be more cold spots: places where the temperature is below the dew point.

A tightly sealed house with long air exchange times may have more problems due to accumulation of excess moisture from cooking and bathing.

A house in a humid climate will have more problems because of the higher humidity of replacement air in the house.

A house with fairly rapid air exchange (< 3 hours) whether from air leaks or forced ventilation is less likely to have problems.

A house in a dry climate is less likely to have problems.

I don't worry about it here in central Alberta. We have a dry climate, and generally have to keep adding water to the air to make it comfortable. We heat with wood, and the house is frequently as cold as 50 F or as warm as 75 F. Sometimes at the same time if we are running only one stove.

Determining which of the above applies can be daunting. Easy way: Measure the humidity. Have several instruments scattered through the house. You are looking for rooms that have humidity levels above 80% for extended periods of time.

You can also check rooms that are closed off. Closets on outside walls especially, and see if there are traces of mold and mildew. Crawl spaces are another place to check. Remove exterior switch covers, and use a fiber optic scope and look thorugh the holes in the outlet box. Peer under siding.

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