I have a thermostat RTH9580. Why do I have emergency heat under system AND heat which sometines switch automatically to auxilliary heat?

The problem with this: A heat pump is only designed to operate properly when the temps aren't lower than 45 degrees outside. That's why they have "emergency heat". The reason being, the heat pump absorbs heat from the outside and then sends that heat to the indoor unit, this releasing that heat inside. Most newer units switch automatically, and thus no rewiring necessary. Older units have a switch on the thermostat that allows you to manually switch to emergency heat when the outdoor temps fall outside of the systems designed operating temps. So, rewiring would probably not solve your problem if you live in a colder winter climate. Hope this answers your question.

IF this is for a heating air conditioning system, there is a transformer on a box near the inside unit, it is protected with a fuse and should have a switch on it, check those.

Thermostats don't actually blow anything, the heating system might though. Check the breakers for your heat system, then call a heating specialist. They're really not that expensive.

If your thermostat has an emergency heat setting this means you have a heat pump system.
Yes you need to set the thermostat to heat for heating the house.
The emergency heat setting should never be used unless your outside unit is not functioning.
The emergency heat setting overides the heat pump (the outside unit will not be energized).
The emergency heat setting will run the auxillary heat (heat strips) only.
When the thermostat is set in the heat position the heat pump will run to heat your house.
If the heat pump can't keep up (extreme cold) then then the auxillary heat will kick in to augment the heat pump until it satisfies the thermostat settings. If your room temperature gets 2 degrees below your thermostat setpoint, your auxillary heat will kick on. Example, say you are going to be gone a couple of days and you turn your heat down to 60 degrees. When you return and it is 60 degrees in your house, you turn the thermostat up to 70 degrees. Since you are turning the temperature up 2 degrees or more (10 degrees in this case) from the 60 degree room temperature then the heat pump will come on and the auxillary heat strips. The unit will continue heating like this until the temperature in the house gets to 69 degrees and the heat strips will turn off and the heat pump will continue to run until the 70 degree setpoint is reached.
Hope this helps.
SeagullAC

I believe the unit you are describing is a heat pump. Heat pump are great when the temperature isn't below 30 With low ambient temps. outside it is much more efficient and comfortable to run aux. electric heat from the heat pump.

W1 and E on stat need tied together. When W1 comes on wire where all heat elements come on. On the outside unit defrost board set the 45-60-90 to 45 and see if that takes care of the frost problem.

I think you probably have a heat pump. Aux heat is electrical resistance heat coils that produce heat when the heat pump can not produce enough to keep the temperature up (caused by low outside temperature or a problem with the refrigerant system). This resistance heat can be switched on by the emerg. heat button. It also can come on automaticlly (sp) and will be indicated by the aux being shown on the thermostat. Sometime if you set the heat up several degrees by thermostat the aux will come on to help the system catch up to the desired temperature setting. The emerg. heat is a way to turn on the AUX manually. If you do not have a heat pump system then it is possible that you have a heat pump thermostat installed on a non heat pump system. Emergency heat and Aux are both the secondary.

Hope this makes sense1

Bob

Sorry, neither of these answers are completely correct.
You have a heat pump (or the wrong thermostat). Let's assume you have a heat pump.

In air conditioning mode, it works like every air conditioner you have ever had, but...

In heat mode, it reverses its operation. Have you ever felt the air coming out of the outdoor unit of your A/C unit? It's hot, isn't it. And the air coming out of the indoor unit (out of the registers) is cold. Now for a heat pump to produce heat it simply runs the air conditioner in reverse and the heat comes out in the house and the cold is released outside. Neat, huh!

Here's the problem with heat pumps...when it is really cold outside the heat pump can't produce enough heat to heat your home. So it has an additional heat source called "Auxiliary Heat". This heat comes on automatically when the house doesn't get warm enough. The source of this heat is based on the region of the country you are in. North/Northeast generally have oil heat, other regions have gas, and still others have to use electricity to heat. In Texas, we usually use electricity as the supplementary heat on heat pumps. VERY EXPENSIVE!

Now the "Emergency Heat"...this is exactly as stated in Solution #2. This is manually turned on by YOU at the thermostat when your heat pump fails. This turns on the auxilliary heaters and turns off the heat pump (remember, the reverse air conditioner). Again, this can be quite expensive to run if your heat source uses electricity! Gas and oil may be cheaper. The emergency heat is only designed (normally) to keep the house livable (not comfortable) until the Heating Tech can get out to you and fix your heat pump.

Something else you should know. It is normal for a heat pump's outdoor coil to frost up during heating mode. It will detect this and go into DEFROST mode and melt the frost off the coil. While it is doing this, it will turn on the auxilliary heater to keep the air blowing in the house at a reasonable "warm" temperature, but it will not be as hot as normal. In fact, heat pumps produce a lower temperature heat than traditional heaters. So the air may feel cooler during heating than you are use to anyway. This is normal and is not a sign of a problem.

So what do you do: Set your thermostat to the temperature you want and set the controls for HEAT/COOL and FAN-AUTO/ON and leave the EMERG HEAT off unless your heat pump breaks.

As always, keep your filters clean and your outdoor unit's coils clean and free of debris.

Hope this explains your question for you!

Are you referring a to an electric furnace providing the heat, the heat pump providing the heat, a heat pump providing heat usually with an auxillary/emergency electric heating unit, or an air conditioner with an electric furnace attached? If your system normally uses a heat pump for the heat normally, there is an eletric auxilliary heater. You'll probably need to turn it on at the thermostat manually when the outside temp gets below 40 degrees. If you have it nice system, it might do it automatically. If you're referring to the electric heater being rated 8 kw, it'll run using 8kw when you turn it on. It doesn't have the ability to change what heat rating it is. If you're refurring to the heat pump system being rated 8kw, you're probably mistaken. A heat pump might possibly consume 8kw to run the system but that can't be a measure of the system's capacity. Heat pump measurement units are rated in tons, but the system will always run at the same ton capacity whenever it's on, provided it doesn't need any maintenance. Some commercial air conditioning and heating systems have to ability to modify their power output based on the outside temperature, but I doubt you're dealing with that kind of thing.

This is the corrcet wiring:
G - G fan relay
R - RC1, RC put a jumper RH ( to supply power to the cool and heat)
L - no wire connected (malfunction indicator) tape- off that wire
E - Emergency heat relay
B - W/B ( reversing valve in your heat pump energized during heat )
W2 - Auxilliary heat
Y - Y1 ( compressor contact)
O- Y/O ( reversing valve is energized during cool)
make sure that the system selector is on heat pump position.