fan forced wall heater
Hello, I would like to know about wiring a dimplex rdh series 2000w 240v wall heater. Can I hook up two heaters to one source of 220 wiring?

Yup you can wire them together. 4000/240=16.6A.
In Canada you can wire to the calculation, which would be #12 wires. According to our codes we have to bump for the breaker which would make it a 30A breaker. The USA is probably differnet, but someone should chime in and say how they do it in the USA. It depends on how your thermostats are hooked up, if they are built in you have to take a feed to the first heater, and then a feed from the first heater to the second heater. If the stats are wall mounted there are numerous ways to do it depending on the layout of everything and which way will use the least amount of wire. 
4000 watts at 240 volts = 16.6 amps. This is technically a code violation. It is done around here on a very regular basis though. There is no hazard involved, just a technical violation.
I've connected plenty of 4000 W loads to 20 amp breakers, had them inspected, and all have passed. Only an inspector with a '10 pound badge' would fail this installation. Rob 
And each heater may only need #14 wire 'cause it only carries 8.3A,
HT#1 ACHT#2 unless you daisy chain the heaters. ACHT#1HT#2 
Codewise, about the only time smaller wire is allowed is with motors, A/C units, and welders.
I realize that the load is smaller, and #14 would hold up just fine for the next several hundred years, but I'd use #12. Rob 
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Heating units
The NEC requires that conductors supplying fixed electric space heating equipment be rated 125% of total load. So 16.4 amps x 1.25= 20.75 amp. Need # 10 conductors.

True enough, but as I stated earlier, I don't know how many times I've connected 4000 watts to a 20 amp 240 volt circuit, had it inspected, and passed. I think very few inspectors are nitpicky enough to fail this installation.
There are code violations that are simply too technical to go after. Most inspectors know this, and are reasonable with minor items. Rob P.S. If you want to get ultratechnical, there are two heaters. Each heater draws 8.3 amps. 220.5 (B) states "Where calculations result in a fraction of an ampere that is less than 0.5, such fractions shall be permitted to be dropped." Therefore, the result of the calculation is exactly 16.0 amps. 16 X 125% = 20. A 20 amp breaker is indeed compliant. 
Calculations
Any 20 amp stab in circuit breaker is rated at 80%. A 20 amp breaker will trip at around 16 amp. It is not only not compliant, it won't work. Regarding dropping the .5, when you do the calculations and the load is 20.75, you cannot drop anything, .75 larger than .50. In other words,if the total branch circuit load is 20.5, the .5 can be dropped. On a practical note, no professional electrician would suggest or install this with #12 wire. I don't believe in " it works so it must be right". We go by the NEC which, in our trade, is adopted as a legal document. I cannot tell you the number of times DYI'S have done noncomplaint installations and created problems. I prefer not to be part of it.

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Breaker size
I had a job inspected and I had 18 amps on a 20 amp breaker. Inspector turned it down. I fought but lost. Asked Cutler Hammer Rep and he told me all stab in c/b's are only rated at 80%. That's what the inspector giged me on. That's where this thought comes from. Brian

According to the trip curves in my Square D book, a QO120 (20 amp single pole) will carry between 100 and 120% of its rated current for more than 300 seconds (5 minutes). Anything over 300 seconds is considered continuous.
Nowhere do I see any breaker that will trip at less than its rated current. If a 20 amp breaker and #12s will not work, and considering how many I've installed, where's all my callbacks? Don't you think there'd be at least one? In over 19 years, there have been zero. All code is written based on past experience, and local jurisdictions are allowed to ammend it, again based on experience. The obvious experience of the inspectors around here is that 4000 watts on a 20 amp breaker using #12s does not constitute a hazard. If 220.5 (B) is applied to the load calculations, then this installation is indeed compliant. 8.3 becomes 8.0. 8.0 X 2 = 16.0. Rob 
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