The popular opinion seems to be that all the power than an asic miner consumes ends as heat, so they are as effective for heating as a heater.
So, if you are going to pay for that electricity anyway, better put it through a miner, so you offset some of the cost with the bitcoins it makes.

Is that really the case though? Are they as effective at producing warm as the conventional stuff and which ones? Since there are many types of home heating devices, each with different effeciency.