In the immediate postoperative phase after surgery, heat and swelling in the knee are very normal as this is part of the normal inflammatory action to the surgery and should gradually settle down over the first two postoperative weeks. If you notice that your redness and swelling appears to be worsening, this is something that you should inform the surgeon immediately, as it could indicate the presence of an infection and you should seek the attention of your surgeon right away for further examination.
However, studies have shown that knee replacement surgery in general, temperature differences between the surgical knee and the nonsurgical knee can persist for up to 2 years after the operation. As such if your knee appears normal and not swollen, but feels warmer than your other knee, this would likely be a normal finding. However, if you are concerned then you should contact you surgeon and consult with them as they will be able to reassure you if everything appears normal, whether there may be a problem, and if you will need further treatment.