We recently had our furnace serviced through the local weatherization program. They cleaned it and replaced the filters. We tried to use it last evening however it is only blowing cool air. Any help would be appreciated as we are not familiar with furnaces and are not sure what to do.

We recently had our furnace serviced thru the local weatherization program

First I would call them back since they probably messed it up to start with.

Next since you are not familiar with furnaces I would check to make sure the thermostat is set for heat and the switch on the furnace is set to heat if the furnace is so equipped with a heat off cool switch to start with.

Once again Hvac is correct. Although they may not have caused the problem, they should have made sure the funace was working properly before they left. However, if they worked on the furnace, then it worked fine for days or weeks or months, than it may just be a coincidense that you are having a problem now. Kind of like having your oil changed and blaming the mechanic for your brake lights not working.