[FullRangeMan]

Reviewing your case some facts are clear>
1) The power company is supplying tension at the appropriate value.

2) The 120V tension is insufficient for your consumption especially with this giant heater on.

3) The 11A load of this heater is an industrial service that requires wiring of at least AWG 8 rigid wiring, not stranded wire and obviously you need higher tension supply as 220V or 360V for a safe use, high consumption with this low tension of 120V will increase your electric bill and may heat up the wiring, which can result in circuit breaker shutdown or fire.

4) By the tension imbalace mentioned previously looks like your CB panel have few brakers, maybe 1 or 2.

5) Would be good for your wallet and for the security of your home you ask the power company for higher tension service as 220V or 360V (three-phase), this single phase of 120V is a basic service suited only to single boys small aptos, not a family house.

6) This imbalance cannot happen and demonstrates there is a major problem of installation or under-dimensioning of wiring or voltage leakage.

Take care.

[ctviggen]

In the US, a 15 amp circuit requires 14 gauge wire; a 20 amp circuit requires 12 gauge wire.  Even with 100 amp service, there should be 220v coming to the house.  In the breaker box, the phases are split into the "right" side and the "left" side.  So, two breakers in the same horizontal "line" are on two different phases.  To get 220v to a device, a breaker fits into two vertical slots, and thus has two phases (typically, red and black wires, one wire going to each phase). 

If there are any open slots in the panel, you can take the cover off and see what I mean. It'll be harder to see if there are no open slots.

100 amps is not bad, assuming you have things like gas stove/cooktop, gas clothes dryer, no AC, etc.  It's when you start loading the system with a bunch of high-demand electrical (stove, cooktop, clothes dryer, air conditioners, heaters), that it becomes an issue.

[Digi-G]

I thought this thread was going to be about the Hardy Boys or The Three Investigators.   

[Speedskater]

Getting back to reply #16.
Those are extremely bad reading!
You need a skilled electrician.

* * * * * * * *
ignore reply #20, it has some major mis-understandings.

[HAL]

I agree about an electrician being needed.  You have nearly 95 watts of power being dissipated in wiring or socket. Something might catch fire.

For an 1800 watt appliance that is 120V@15amp and nothing else on the circuit breaker.  It should be a 20amp circuit with correct wiring size and breaker if more loads on the circuit.

The electrician can also test the ground wiring while he is there and repair/replace as needed.

Another thing to check is the meter base.  It might have corroded and give problems.  That your electrical company can do for you.  I had that problem and caused high line distortion until corrected.

Good luck.

[Speedskater]

An 1800 Watt appliance should/must have a 20 Amp plug. Only 20 Amp circuits are permitted to have 20 Amp receptacles.

[FullRangeMan]

Disregard post #23 its the constant yankee envy.

[Peter J]

Disregard post #23 its the constant yankee envy.

What is it you think we envy, FRM? The post Speedskater called out is fraught with misinformation and mostly irrelevant to situation described by original poster.

[thunderbrick]

Disregard post #23 its the constant yankee envy.

I think you have it wrong.  We "yankees" don't envy you; it's the other way around...