Just as one may use fire to cook and bake, so one may to use fire to heat the house when it is cold. If the fire in a wood-burning stove is too small to properly heat the house, more wood may be added to make it hotter. If a heater uses kerosene or gas, one may add fuel to increase the heat it produces (SA 511:1). Even though heating the home is not tzorekh okhel nefesh, there is an accepted principle that once lighting a fire is permitted for okhel nefesh, it is permitted for other purposes as well (“mitokh”). This principle applies as long as the other purpose is something that most people find enjoyable (3:6 above). Heating a cold place falls into this category.
Candles may be lit for a Yom Tov meal, even where the electric lights already provide enough light, because extra candles contribute to a joyous atmosphere and honor the festival. However, one may not light more candles than is generally accepted for this purpose. One who is afraid of the dark may also light a candle.
We have already seen that a new fire may not be lit on Yom Tov. Therefore, in all the cases mentioned above, the candles should be lit from a pre-existing flame. If it is difficult to bring the candles close to the pre-existing flame (as sometimes happens when a yahrzeit candle has burned down), one may light a match or wood chip from the pre-existing flame and use the new flame to light the candles. After lighting a candle, the match may not be put out, as doing so is not tzorekh okhel nefesh, and is thus prohibited on Yom Tov. Rather, the match should be put down gently and allowed to burn itself out.
Candles may be lit in the synagogue to honor the Shekhina that dwells there. As we said above, once lighting is permitted for okhel nefesh, it is permitted for other purposes as well, such as for a mitzva. One may light candles in a synagogue following Minḥa near the end of Yom Tov, even though they will burn only a short time on Yom Tov; this is not considered preparing for the weekday, since the Shekhina is being honored on Yom Tov, when they are lit (SA 514:5).
If one wants to light a yahrzeit candle in memory of his parents, he should light it before Yom Tov. Since there is no mitzva to light such a candle, and it serves no Yom Tov purpose, it is not proper to light it on Yom Tov. If one forgot to light the candle before Yom Tov, he should light it where it will provide extra light, whether for a Yom Tov meal or in the synagogue. If this is impossible, and he would be very upset were he not to light, he may opt to be lenient and light the yahrzeit candle anywhere, since there is a mitzva element in honoring the memory of one’s parents (BHL 514:5 s.v. “ner”).