I have purchased two different types of home heaters - both worked well for many years. Last year I wanted to plug in a clock radio and noticed that the wall where the heater was plugged in was slightly warm. I checked all the outlets in the room and found them to be a bit warm. I turned the heater off and the warmth went away. Now I'm a bit concerned. Do I need an adapter, stop using small portable home heaters, what?
Line voltage varies slightly by home and by region. 110v and 120v are more or less interchangeable, nominal approximations. 117v is (was?) an average. The current spec is 120v +/- 5% if I'm not mistaken.
Your heater draws a lot of current, and weak points in the circuit, such as plug connections, will often show some heat accumulation.
It is a bit odd that other outlets would be warm as well, though. It's possible that the wiring runs through the outlet side jumpers, but that should be a sturdy connection that isn't a high-resistance point.
Anyway, "slightly warm" isn't too concerning. Many devices will do that, such as battery chargers. When it approaches hot to the touch you have a real problem. Keep a close eye on it and try not to rely on portable heaters for long periods of time.
Flexible cords used in small appliances usually use smaller wire than the house wiring (as allowed in table 400.5.a.1 of the NEC) These cords will get warm to the touch on space heaters. If the outlets are getting warm in that room they are probably daisy chained using the back stab connections. Back stab connections have a very small contact area and heat is created with a heavy load at the outlets. To eliminate the heat from the additional outlets the wires can be pig tailed (incoming hot and out going hot tied together with a short piece of wire also going to the outlet) pig tailing the neutrals and hots should eliminate the heat at the other outlets. You ask should the outlet get hot? No it should not be hot but may be warm.
Undersized Romex and the actual outlet amperage rating will cause heat. For example, if the builder used the cheapest Romex available and the cheapest outlet you'll be lucky to be able to pull 9 amps reliably, although the outlet is rated at 15 amps. Normally most household outlet or wall outlet circuits are connected to a 20amp breaker, usually not more than 6 outlets are serviced by that breaker per NEC code. However, I have found that code isn't always followed. If your outlet is getting hot by utilizing a source, AKA space heater, this means that the outlet and the wire supporting that outlet is to be questioned. In layman's terms , you need to have the electrical checked by a professional, to continue to utilize an appliance that makes said outlet hot is only inviting a fire.