Also, he only hooked up the 10kW which is operating now, and left the 3rd strip disconnected

 

Because the third strip would put you over your 60 amp breaker.

 

Only a load calc would tell, but you probably will be OK with 10kw plus the heat pump in VA.

Most of the time, mfrs. have the first 10kw as 1st stage, then then next 10kw (or in case of 15, 5kw) as 2nd stage. The heat kit could be rewired so each 5kw bank can be staged individually but probably not worth the controls or the effort.

 

10KW is probably pretty close to what you need. Give or take 2KW.

 

Certain models of the carrier heatstrips can be staged to run 5-10-15. There is a model that runs 3-6-9. Without a load calc, do not know what you really need, but as stated before "typically" in VA 10kw is fine.

 

15 kw usually have a 30 and 60 A circuit to them. If you were in emergency ht on a cold day, you may notice the difference.

some systems disable the extra strip above a preset outdoor temp. It would take a 3three stage tstat or a time delay switch to run the 3rd strip as another stage of heat.

Had a gynecologist that wanted to be able to disable the strips manually, so we put toggle switches on the tstat and modified the control wiring.

 

Had a gynecologist that wanted to be able to disable the strips manually, so we put toggle switches on the tstat and modified the control wiring.

Did it really matter he was a "lady Parts doctor"?....lol im still cracking up..

but you guy are all right, you can do anything with proper control wireing, with this "global warming" may be worth upping the amps and getting that full 15kw if needed but thats up to homeowner. just make sure they are on a staged T-Stat so they dont all come on at the same time.

 

Yes you need the full 15 kw, You can double check with load calc.

 

10kw would be borderline, hard to say w/o a load calc. I wouldn't worry about having 3 stages, just do 10kw first and 5 on second. You will need 20A per 10 kw of heat plus your blower (figure 10A). Also you need to have large enough wiring to handle the load, not just a large enough breaker. You would need at least #10 copper for the extra 5kw.

 

<snip>You will need 20A per 10 kw of heat plus your blower (figure 10A).<snip>

By my math you need 41.66A per 10kw of heat @ 240VAC.... 10,000 divided by 240 is 41.66.

 

Who knows what you need without being there. 10 is probably fine. If it's cold outside or as cold as it gets there and it's keeping up, you're probably fine. You can stage anything the way you want it. If the unit isn't equipped to run it this way, you might have to pay extra $$$. What size heat strips did your old air handler have? If you had a 10, then I wouldn't sweat it much. My biggest worry is he's planning on putting an 80 amp breaker to run all this. Is the wire feeding the air handler big enough to handle this extra load? If not, you might have an issue with that, such as a fire.

 

Heat strip staging

Thanks. So can a 10kw heat strip unit be staged with 5+5? or must you have a 15kw unit in order to do staging? It was explained to me that the only the 15kw unit allows a setup for staging the strips??? ALso, where does the setup done? in the thermostat or at the air handler where the board is? And is there an easy way where I can check if they are coming on in stages?

thanks again


also, Someone earlier in this said that using a 10kw unit that comes on full with no staging would be fine. Did I understand that correctly?

 

Thanks. So can a 10kw heat strip unit be staged with 5+5? or must you have a 15kw unit in order to do staging? It was explained to me that the only the 15kw unit allows a setup for staging the strips??? ALso, where does the setup done? in the thermostat or at the air handler where the board is? And is there an easy way where I can check if they are coming on in stages?

thanks again


also, Someone earlier in this said that using a 10kw unit that comes on full with no staging would be fine. Did I understand that correctly?

10KW coming on not staged is fine. During defrost you'll prefer 10KW over 5KW.

 

You can stage 5 and 5 but you would need to add an extra heat sequencer or contactor (depending what brand of a/h you have) and have a 2 stage thermostat. Personally, I don't like staging anything under 20kw.

 

Don't like staging anything under 20KW?>? why would you not, with the technology of the new t-stats and the right sequencing you could have it set up so you dont have 20KW of heat blasting all at once! and watching the Meter spin around like crazy. If you have a heat pump you dont need 20KW just for defrost.

 

True. Why not add strips in steps as needed to assist the pump. Only use what you need.

 

My mothers 3 ton infinity heats her 2300 sf townhouse to below 8f. I know this because the crew didn't know how to set up the controller, didn't tell me, and she called saying "the house is staying 70, but the air coming out of the registers seems kinda cold".

If what you have turns out not to be enough where you are its likely something is pretty wrong with your house. An energy audit should tell you what's wrong with your house. Adding more heat is not always the right answer. Slow the losses.

 

Exactly. You can't get around the physics of it. If your 10 kW strip is only pulling 20A, it is only giving you 5kW of heat unless it is being run at 480v.

The strips are normally 5kW each and more are added to get to whatever total you need.

Lower voltage will give lower amps and you take a double hit on power. As an extreme, say you connected these elements to 120v. You cut the voltage in half, the current is also cut in half, this means that the power (Power = V X I) is cut to 25% of initial value (10kW of elements would produce 2.5kW of heat).

 

lady parts doctor was doing the change due to complaints in the exam rooms. he didn't have any complaints for the heat

 

Wow...........I was beginning to question my knowledge of electric but then i did the math. As stated Ohm's law and between 210-240 volts 41.66-47.61 amp difference.

I read his first post on that and let it go. And as usual you guys would not let it ride. Constant policing here. But thats a good thing. Keep everyone in check. :angel:
Good job westval !

 

Not looking to keep anyone in check, just thinking outloud through the keyboard!utergreet:......during heating season that's the only time I get to stop and think.....:grin2:

 

If there is enough amperage to the air handler you could let the thermostat use 10KW for AUX heat and use the other 5KW for defrost. Most air handlers just need a simple wiring change to set them up that way, connect W1 to the thermostat, W2 to the white/defrost from the condenser. If the heat pump can't keep up then only 10KW of heat would be added instead of the full 15KW. If the temp dips too much with only 5KW in defrost the thermostat will bring on the 10KW aux heat for a total of 15KW. Wiring this way has some potential to save some $$$ in defrost at the expense of cooler air from the registers.

 

Old thread, closed as too many previous posters are not Pro * members.