Low 70's is a high temperature for most ale yeasts (excluding several Belgian strains, some of which can go all the way up to the 90s). The particular yeast you are using - Wyeast Irish Ale - tends to be very estery once you get into the high 60s and low 70s. Here is the description from their website:
This yeast ferments well in dark roast worts. Beers fermented in the lower temperature range produce dry and crisp beers to fruity beers with nice complexity in the upper range. Ester production is enhanced with fermentation temperatures above 64 degrees F (18 C). Flocculation is low to moderate with filtration typically required.
Temperature Range: 62-72F, 16-22C
Alcohol Tolerance: 10% ABV
Taking this into consideration, I would try to hold my fermentation temperature close to that 64 F mark if you don't like estery beers - this shouldn't be too hard to do in the winter. Just remember that heat generated during vigorous fermentation can cause the actual temperature of the beer to be up to 8ish degrees higher than ambient temperature - probably less for you because you under pitched.
Fermometers are a nice, cheap and simple way to know the temperature of your beer (almost everyone carries them). If you keep your fermenter in water to help regulate the temperature, just be sure to stick it on horizontally above the water line. They get kind of screwy after prolonged exposure to water.