Will the rise be noticeable? Short answer, yes.
Long answer: It will not be as noticeable as GPU folding would be. However, if you pay the bills, you will feel it. If you wish to compute it, and you have a Kill-a-Watt, you need to take the wattage of the system at load and subtract from that the wattage of the system at idle. Multiply that by the number of hours daily you wish to fold, then by 30.4375 to convert daily into monthly. This is how many extra watts your folding will use. Multiply by the going rate for electricity in kW-hr (better to aim high, say 20c) and then divide by 1000. That will give you the monthly increase in cents. (Divide by 100 for Euros.)
In my case (GPU/CPU mixture), my PC produces about 40-50% of the month's total electric bill. If you consider that it causes the A/C to come on more, that would be more like 70% attribution.