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A new study of over 380,000 web-based consumer broadband speed tests (recorded over the past 12-months), which was conducted by comparison site Broadband Genie, claims to have identified that broadband download speeds can slow down by up to 8% and uploads by up to 27% on the hottest days of the year (usually heatwaves).
The study was conducted by taking the average download and upload broadband speed from typically the hottest part of the day (11:00 – 15:30). This was then compared to broadband speeds recorded on the five hottest days of the year in the same hours of the day.
Upload speeds took the biggest tumble, dropping 27% on the hottest day, recorded in Brogdale, Kent. On the same day, download speeds were also 8% slower. On average, upload speeds declined by a tenth (10%) and download speeds dropped 3% vs. speeds on an average day.
However, it’s worth pointing out that the issue here is likely to be less down to your broadband connection and more with your router, since the chipset (CPU) may automatically choose to throttle back its performance as part of thermal management during very hot days (i.e. helping to avoid a hardware crash) – particularly if the device is under heavy load at the same time.
However, in that sense, it may not be entirely fair of the study to describe this as being due to “broadband speeds“, since the slowdown is less likely to be caused by your ISP and is more of a local network issue. “Our research shows hotter temperatures consistently take the edge off your broadband speed. The main weakness is your home broadband router. If the internal components get too hot and overheat, it will slow down or even cut out. If surfers aren’t careful, it could grind your connection to a halt,” said Alex Tofts, Strategist at Broadband Genie.
Table: Broadband speed on the hottest days of a year
| Hottest temperature recorded | Temperature (°C) | Download speed change vs. overall average | Upload speed change vs. overall average |
| Brogdale, Kent | 35.6 | -8% | -27% |
| Heathrow, London | 32.7 | 0% | -3% |
| Wisley, Surrey | 32.6 | -1% | -2% |
| Coningsby, Lincolnshire | 32.2 | -5% | -11% |
| Chertsey, Surrey | 32.2 | 1% | -9% |
As we’ve said before (here), most router manufactures are aware of thermal management and design their hardware to operate at temperatures of up to around 40c (varying a bit between manufacturers). Sadly, an overheating broadband ISP router is something that can happen, although even many of the devices with a stated tolerance of up to 40c may actually continue to function for a handful of degrees past that point.
However, experiences do vary a lot, and we should point out that your mobile phones, laptops, game consoles, tablets and other electronics may also run into their own issues (i.e. the router may not be the only source of performance problems that can impact your network).
Sadly, the study doesn’t date its temperature recordings or include a technology split, since it would have been interesting to know whether FTTP connections are just as likely to suffer from such issues as copper-based (ADSL, FTTC etc.) ones. If the primary cause is within the end-users network, then the answer may be yes. But equally, full fibre infrastructure should be more resilient since a lot of the related processing hardware will be retained back at the air-conditioned exchange/data centre (some areas may also place related networking kit inside more exposed local street cabinets).
On the other hand, it’s worth noting that the headline figures given in the study (8% and 27%) are clearly location specific. But in other areas the results show only a small to modest change, with Heathrow being largely unimpacted for downstream traffic and Chertsey actually showing a gain of 1%. Most of the figures show fluctuations that are thus a bit too small for drawing credible conclusions and, in fairness, the UK isn’t exactly a particularly “hot” country, so far as the world goes.
Finally, we should point out that we all live in different buildings, where the resilience to internal temperature rise will also differ – often significantly. As a result, the outside temperature measurement on a specific day does not tell us the whole story.