Electric back up strip heat

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nizak

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Need help determining if HVAC contractor is grossly oversizing the electrical back up strip heat their installing on a new residential build with geothermal system.

Would you figure it similar to electric baseboard heat? For instance, 8-10 watts per sq/ft?

Or is ita totally different formula since you already have X amount of heat supplied by the system and you're supplementing it?

The answer I'm getting from HVAC people is : That's what our chart calls for.

Thank you.
 
Why are you second guessing the hvac guys. They do use charts that are generous that usually take into consideration the R value of walls and ceilings, etc and also window sq. ft.
They are probably sizing it for when the geotherm breaks down and the strips have to heat the entire place. They may be staged so that all the elements don't come on at once.
 
Dennis Alwon said:
Why are you second guessing the hvac guys. They do use charts that are generous that usually take into consideration the R value of walls and ceilings, etc and also window sq. ft.
They are probably sizing it for when the geotherm breaks down and the strips have to heat the entire place. They may be staged so that all the elements don't come on at once.
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When I spoke with the Co. 3 months ago I asked for loads associated with the system they were installing I was told 10KW strip.

Now it’s 20.
 
You are up in the North s it does get cold but around here they install backup heat to just keep the house at 60 so you don't freeze.
 
20kw is also about 66K btu. If they we installing a gas furnace, would a 70k or 80k btu unit be considered large? Ask for the hvac guys manual J calculation. If he said what is that, he seat of the pants' it. It indicates the heat loss and heat gain of the building which is where you start to size furnaces and air conditioners.
 
Doesn't make sense for backup heat to heat the entire house. Geothermal is better than a heat pump and can operate year round.
 
tthh said:
Doesn't make sense for backup heat to heat the entire house. Geothermal is better than a heat pump and can operate year round.
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Not following. You are saying only provide back up for part of the house?
 
tthh said:
Doesn't make sense for backup heat to heat the entire house. Geothermal is better than a heat pump and can operate year round.
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The back up is for when the temp gets so cold that the geotherm can't keep up and it is also for when the geotherm unit goes on the blink
 
I get the emergency heat thing, but geotherm shouldn't need this I would think. I suppose they could have the coils in a lake or something, but if they have the coils in the ground or a deep well, there should be no need for emergency heat????
 
Dennis Alwon said:
2000 sq. ft ? 20 kw is ridiculous. I would bet with today's insulation etc If they l
Dennis Alwon said:
The back up is for when the temp gets so cold that the geotherm can't keep up and it is also for when the geotherm unit goes on the blink
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If they lose power their totally SOL. Home has no alternate fuel source of any type.Natural gas is available and could be run right along with the power.
 
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texie said:
Nit picking here. Geothermal is a heat pump. But I suspect you know that.
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Yes, "regular" heat pump is air sourced heat exchange heat pump and geothermal is liquid sourced heat exchange heat pump. Typically running some coolant through coils in the ground or possibly down a well. That's why I don't understand why emergency heat would be needed. Now, I do understand you can run the coils in a lake and if you were in some parts of Canada, maybe there's an issue with that one.
 
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tthh said:
Yes, "regular" heat pump is air sourced heat exchange heat pump and geothermal is liquid sourced heat exchange heat pump. Typically running some coolant through coils in the ground or possibly down a well. That's why I don't understand why emergency heat would be needed. Now, I do understand you can run the coils in a lake and if you were in some parts of Canada, maybe there's an issue with that one.
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My in-laws in Missouri ran the coils from their water source heat pump in the pooled outflow of a fast running spring, so the water temperature was close to uniform all year round. No need for backup resistance heat there.
 
nizak said:
Need help determining if HVAC contractor is grossly oversizing the electrical back up strip heat their installing on a new residential build with geothermal system.

Would you figure it similar to electric baseboard heat? For instance, 8-10 watts per sq/ft?

Or is ita totally different formula since you already have X amount of heat supplied by the system and you're supplementing it?

The answer I'm getting from HVAC people is : That's what our chart calls for.

Thank you.
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I have a house I'm wearing right now. It's about 2600 ft² and I and I was told they were going to put in 15KW heat strips

They actually installed 20KW

Sometimes they just put in whatever they have in their shop or whatever is the most convenient to get their hands on

From what I've seen, about 7 or 8 watts per square foot seems right for Missouri
 
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