I have to maintain my pigs cage at 17-19°C at all times as I have an old lady pig with ongoing respiratory issues. The heating only comes on for 1-2 hours in the evening (if at all) so it can get quite chilly. (The room used to be completely unheated and would stay at 13°C during the day for most of the winter, waking up to finding ice on the inside of the windows is not very fun!)
I make sure there are at least twice the number of warm fleece beds as there are guinea pigs and ensure that any even slightly damp pee pads in beds are removed and dried. Their hay area is kept topped up and cleaned daily so that they don’t go and sit in wet hay.
Something I find really helps is shutting all blinds and shutters as it begins to get dark, especially when it is very cold. I find that a lot of heat is lost through uncovered windows.
If you don’t already, I recommend getting a digital thermometer. Sometimes it feels a lot colder than it really is. I think that as a room temperature they only need around 18°, but they will usually be slightly warmer than that as they spend a lot of time buried in hay or snuggly beds.
If it is very cold I will give them warm oats made into a sort of (non-cooked) porridge with either carrot or apple added in, I know how much a warm meal warms me up and can imagine it does the same for them as well as giving them the energy to generate their own heat.
I also have a heat pad each for them which I will microwave and put in if I’m going out for the day and it is particularly cold.
If it gets far too cold (below 16) I do have to give in and I use a very old oil radiator as I would rather the cost over a dead or very ill guinea pig.
