I would first choose to not use the word “penalty” in this context. A penalty is more like a sentence a court might hand out on conviction for a fixed term in prison.
Rather, the powers of the House are ones it might exercise to try to induce compliance with the order of the House. Assuming for a moment that the matter advanced to where the House made an order that the person show up and testify before the committee and the person didn't, I think the House might send for the person to be apprehended and brought before the committee to testify. If the person did not testify on that occasion, the same order would say, “to be held in custody until such time as he or she does testify”.
That has been done in the past. They're held in custody but released at the end of the session. The point is that the reason for the imprisonment is to induce compliance, not penalize them by sentencing them to a period of months or years. Once they comply and are ready to testify to the satisfaction of the committee and the House, that's the end of the incarceration and the person goes home.
So as far as trying to enforce its proceedings or defend its proceedings against improper or contemptuous conduct, the extreme end is to have the person, by order of the House--directed to the Sergeant-at-Arms--incarcerated until such time as they comply. Upon compliance, presumably they would be released because there was no further need for imprisonment.