I have an Electric Furnace rated at 45 Amps/240v. Would a 45 amp breaker suffice for this unit?

#8 wire for a 40 amp breaker is fine for what you have. You could put a 45 in if you wanted to and #8 wire would still be fine.

90 amps at 220 volts 166 amps at 120 vots

1) You got a FIRE truck coming.

2) Wire is too small.
Problem is NOT circuit breaker.

3) Both 240Volt appliances on same breaker is a hazard, especially if space available in 200 amp service panel for more breakers.

4) Usually each 240V appliance has separate breaker.

5) Circuit breaker trips because of High heat on the wire.
If wire gets hot, it will start a fire inside the wall.

Electric code requires wire-size match breaker-size.

6) If you put larger amp breaker on same wire that is getting hot, then wire will get hotter.
Result: FIRE truck middle of night with folks jumping out window in glass-cut bare run across yard.

7) Each appliance has volts and watt rating on label.
EVERY appliance has label.

8) For example stove might be rated 8000 watts and 240Volt.
8000 watts divided by 240 volts = 33.3 amps
Stove would require 40 amp breaker and 8 gauge wire.

9) How to figure it out:
http://waterheatertimer.org/Color-codewire.html
http://waterheatertimer.org/How-to-install-a-subpanel.html

10) Do same calculation for new furnace.
12000 watt furnace divided by 240 volts = 50 amps.
Use 60 amp breaker and 6 gauge wire.

11) Summary: fixya wants you to be safe, and buy stuff showing in the ads.
Use a bigger breaker ONLY when bigger wire is also installed.
Call furnace installer, the installer should know to check safe wiring before installing.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

1) Manufacturer's warranty will be voided, and I've never seen recommendation that suggests better heating or saving money from replacing 4500W with different wattage element.

2) That being said, you have 240V water heater.
4500Watts divided by 240 = 18.75 amps
5500Watts divided by 240 = 23 amps

20 amp circuit breaker with 12 gauge wire is rated for 80% of load = 16amps
30 amp circuit breaker with 10 gauge wire is rated for 80% of load = 24amps.
http://waterheatertimer.org/Figure-Volts-Amps-Watts-for-water-heater.html

3) You can use 5500Watt element if you have 30 amp breaker and 10 gauge wire.

Look at rating plate on motor.
Look for volts, watts, amps.
Figure with Volts x Amps = Watts.
Amps = Watts divided by Volts
1 hp horsepower is 756 Watts.

Lets say you have 120Volt 2hp motor
So 2 horsepower motor draws 1500 Watts
Amps = 1500 Watts divided by 120Volts = 12.5 amps = so you need 120Volt 15 amp breaker with at least 14gauge wire (as long as motor is located within 50 feet of breaker.)
If motor is farther away, then you need 20 amp breaker with 12gauge wire.

Look at circuit breaker rating.
If motor is 240 and breaker is 120, then it will trip breaker.
If motor is 120 and breaker is 240, then it will trip breaker.
If breaker is for 15 amps and motor draws 20 amps then it will trip breaker.

Generally speaking, if motor and breaker are 120V, then black wire goes to black wire; white wire goes to white wire and green wire connects to bare copper wire.
If motor and breaker are 240V, then wire colors can be different. Black-red or Black-white from breaker connect to Black-red or Black-white at motor.

Add a comment. Say the motor rating and color of motor wires. Say the breaker size and color of wires coming from breaker and I will help you wire the device.

The water heater has two 4500 watt elements.
However both elements are not turned-ON at same time
So the water heater is 4500 Watts

Volts x Amps = watts
Amps =watts divided by volts
Amps = 4500 Watts divided by 240 Volts
Amps= 18.75

So that says a 20 amp breaker ... except for the 80% rule
80% rules says for safety, your Amp rating should be multiplied by 80%

20 amp breaker X 80% = 16 amps
20 amp breaker is actually safe for just 16 amps, and your water heater draws 18.75 amps.

The calculation shows you need a 30 Amp breaker.
30 Amp breaker requires 10 gauge wire.

http://waterheatertimer.org/Figure-Volts-Amps-Watts-for-water-heater.html

It does make a difference as to input voltage. But usually at 11KW this would be a 220V unit and require a 50 amp breaker. 11,000W divided by 220VAC = 50 amps. 230 or 240V input the same 50 A breaker.

Thanks for choosing FixYa.

Kelly

Using the equation I = P/E where "I" is Amps, "P" is Watts, and "E" is voltage, we find that your 5000w circuit will have an Amperage of 20.83. A 22 amp tstat will work, it will just leave you no room for surges. I would suggest splitting the baseboard and using 2 thermostats. Hope this helps

Check the breakers on the unit How many KW--electric heat? Check to see if you have the right wires wired up to the correct breaker cause some units have 40---and ---60 ---amps breakers and your thickest wire could be wired to the 40-amp breakers,, (some 5 KW pullls 19-23 amps respectably some breakers have 7.5 KW heat stips and pulls more and if the wire size can,t cary the amps, then all you have to do is reduce a heat strip.

it is normal for a breaker that is run right on the edge (50 amp and your furnance to use 45) to get weak after a while . the first thing you should do is change the breaker with the same type and amp rateing . it should take care if it