Supplemental Heating in Air Handler over 10kW (Electric Heat)

Status
Not open for further replies.
Chamuit

Chamuit

Grumpy Old Man
Location
Texas
Occupation
Electrician
I have had very little exposure to electric heating in my years. Probably less than 6 units I've touched in almost 30 years of work. With the Snow-mageddon event, I've had a lot of questions surrounding circuits for HVAC units: condensers, heat pumps, furnaces, and air handlers with supplemental heating. Fairly routine stuff except for older homes where the air handler is feed with a 90-100 amp branch circuit.

In my past, I have seen:
1. (What my journeyman called) a double disconnect used. Can't remember if it was fused or not.
2. A primary 60A and a second 30A or 60A circuit brought to separate disconnects.

My question is, for those of you that commonly encounter this scenario, what are the typical methods you employ to handle the 90-100A scenario?
 
Chamuit said:
I have had very little exposure to electric heating in my years. Probably less than 6 units I've touched in almost 30 years of work. With the Snow-mageddon event, I've had a lot of questions surrounding circuits for HVAC units: condensers, heat pumps, furnaces, and air handlers with supplemental heating. Fairly routine stuff except for older homes where the air handler is feed with a 90-100 amp branch circuit.

In my past, I have seen:
1. (What my journeyman called) a double disconnect used. Can't remember if it was fused or not.
2. A primary 60A and a second 30A or 60A circuit brought to separate disconnects.

My question is, for those of you that commonly encounter this scenario, what are the typical methods you employ to handle the 90-100A scenario?
Click to expand...
For what it's worth, I'd think the small subpanel is the way to go.

Adding more panels and circuits isn't going to help if there is a repeat of the scenario. Putting in a fireplace or wood-burning stove for backup would be a smarter move.

I occasionally follow a contractor on YouTube named Matt Risenger who is based in Texas. One of the things he normally does that near gave me a heart attack the first time I saw it was to install a tankless hot water heater on on the outside of a house. Just hanging right there off the side. I wonder how well those faired during the recent event.
 
It's not quite a 90-100 amp scenario.
What you have is either a 15kw or 20kw furnace.

6-2/g for 10kw
10-2/g for 5kw

You can either run a subpanel or separate circuits
 
$8000 electric bills and they're thinking of adding resistant heat loads?o_O
Gas wasn't available either. Talk about being caught between a rock and a hard place.

Sometimes one feeder to a subpanel closer to the equipment is easier. Eliminates additional disconnects if the SE is remote. We've done it both ways.
 
Back in the day when I was servicing residential systems daily, 30KW systems were not uncommon in Texas, and they were generally seen on arrangements that were straight electric heat with no heat pump involved. They were fewer in number but they were out there.
Carrier made and sold plenty of those.
I recall 2 circuits coming in, and then the FCU package had 2 on board circuit breakers. They never fail at a good time either.
After this the confounded ' dual fuel " systems evolved.
 
15 kw is commonplace here.
It might be worth noting, a lot of the 15kw units we have carry a MCA > 55a on the 10kw circuit and a #6 NM would be undersized. Source of a lot of rejection notices locally.
 
augie47 said:
15 kw is commonplace here.
It might be worth noting, a lot of the 15kw units we have carry a MCA > 55a on the 10kw circuit and a #6 NM would be undersized. Source of a lot of rejection notices locally.
Click to expand...


I always hated that. Those units were right at 56 amps or 57 amps. Seriously, irked me to no end.
 
BTW, if the furnace is in a crawl area and you don't have the 110.26 requirements then a panel with disconnects cannot be used for other purpose other than the unit itself.

I haven't done a 15kw unit in a while but some came with disconnect breakers inside the unit and only required one circuit but I think now they usually come with a need for 2 branch circuits.
 
ptonsparky said:
$8000 electric bills and they're thinking of adding resistant heat loads?o_O
Gas wasn't available either. Talk about being caught between a rock and a hard place.
Click to expand...

The $8K electric bills were for people on a plan that let them purchase electricity at wholesale rates with _zero_ hedging. IMHO a _great_ plan if you have some way of seriously dialing back your usage when the prices spike. The whole idea is that electricity rates go up when there is scarcity so that people use less. Unfortunately not many people really understand what it means to buy electricity wholesale with no hedging and no backup to let you turn the electricity off.

Resistance heat makes good sense if you use it very infrequently and can survive with it off.

-Jon
 
Dennis Alwon said:
BTW, if the furnace is in a crawl area and you don't have the 110.26 requirements then a panel with disconnects cannot be used for other purpose other than the unit itself.

I haven't done a 15kw unit in a while but some came with disconnect breakers inside the unit and only required one circuit but I think now they usually come with a need for 2 branch circuits.
Click to expand...
I called the inspector on this the other day. It wasn't for heating strips but for a panelboard change out where the existing panel is in a 5' high crawl space. He said we could replace it in the same location citing exception 2. Now I am not sure what exception 2 is actually telling us?
 
codeunderstanding said:
I called the inspector on this the other day. It wasn't for heating strips but for a panelboard change out where the existing panel is in a 5' high crawl space. He said we could replace it in the same location citing exception 2. Now I am not sure what exception 2 is actually telling us?
Click to expand...
I would think he's referencing what is Exception 1 in the 2017:
Exception No. 1: In existing dwelling units, service equipment or panelboards that do not exceed 200 amperes shall be permitted in spaces where the height of the working space is less than 2.0 m (61∕2 ft).
That seems to apply in your situation.
 
winnie said:
The $8K electric bills were for people on a plan that let them purchase electricity at wholesale rates with _zero_ hedging. IMHO a _great_ plan if you have some way of seriously dialing back your usage when the prices spike. The whole idea is that electricity rates go up when there is scarcity so that people use less. Unfortunately not many people really understand what it means to buy electricity wholesale with no hedging and no backup to let you turn the electricity off.

Resistance heat makes good sense if you use it very infrequently and can survive with it off.

-Jon
Click to expand...

Exactly. A lot of people are crying price gouging that signed up for those plans. Problem is, that's what they agreed to. Griddy, the wholesale provider in my area, sent out emails informing people of the increase in price. They either were stupid or ignored it.

The flip side is that, if you were on a fixed rate plane, the retail agent had to eat those costs.
 
Chamuit said:
Exactly. A lot of people are crying price gouging that signed up for those plans. Problem is, that's what they agreed to. Griddy, the wholesale provider in my area, sent out emails informing people of the increase in price. They either were stupid or ignored it.

The flip side is that, if you were on a fixed rate plane, the retail agent had to eat those costs.
Click to expand...
Folks need to remember that plans like this are basically the same as trading in the commodities market. There is no limit to the downside, or in this case the upside price. If you wouldn't dabble in commodities for love or money, you shouldn't sign up for one of these plans. If you want a glimpse of the future, look at some of the gyrations in the Australian power market. Renewable penetration is much higher there. They've seen prices up to AU$15,000/MWhr (current market cap) in Queensland.
 
If a plan like Griddy were available to me, I would use it.

I have oil heat, am in a climate where I can survive without AC, and can cover my light, refrigerator, oil burner, and computer needs with a generator.

Gadfly is spot on, using this sort of supplier is trading in a commodities market, but it isn't trading commodities futures. If the price gets too steep you can bail by turning off the switch.

But if you are captive and can't turn off the switch, then you essentially are in commodity futures.

I should note that some of the more traditional fixed price suppliers have filed for bankruptcy.

Jon
 
Here's what some folks have been running into. I think this was #2 Aluminum on a 90A breaker. The person who did the installation originally had to do quite a bit of strand trimming to get everything to fit.

I gave a little talk to the group and explained wire sizing and breaker selection. How disconnect and breaker lugs are rated for one conductor and have a size limit. I pulled the specs on the equipment they use and showed them how to read those very helpful labels already there for them to see.

unnamed.jpg
 
That looks like a 60 amp and a 40 amp breaker... Is that correct?

What they needed was a disconnect and then run 2 circuits from the disconnect to the unit. No disconnect is needed if you run 2 circuits back to the panel.
 
In this area the size breakers in the unit itself is often meaningless. The units come with (2) 60s which can serve as disconnects but are often not sized per the nameplate as heat kit decisions vary with specific requirements.
 
Dennis Alwon said:
That looks like a 60 amp and a 40 amp breaker... Is that correct?

What they needed was a disconnect and then run 2 circuits from the disconnect to the unit. No disconnect is needed if you run 2 circuits back to the panel.
Click to expand...
@Dennis Alwon yeppers.

What was done here was the 90A (breakered) circuit was run from the panel to a single 60A (rated) disconnect then into the air handler, then jumped from one 60A breaker (line side) to the next with #10 wire.

Ckt1, where the home run was landed, feeds that air handler and one heat strip.
Ckt2, where the two 5kW heat strips are tied in, was fed with the #10 jumpers.
 
Status
Not open for further replies.
Top