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testing emergency heat


John Dirks Jr
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I know you should not run a heat pump in the heat mode during hot weather. What about the emergency electric coil? Is it safe to command that in hot weather? Will the thermostat E heat function bypass the heat pump heat mode all together? What about programmable electronic thermostats? Can they complicate the testing of E-heat in hot weather?

I know I should know this but I just want to be sure. If I can get an answer this time, I'll never have to ask it again.

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Originally posted by John Dirks Jr

I know you should not run a heat pump in the heat mode during hot weather. What about the emergency electric coil? Is it safe to command that in hot weather? Will the thermostat E heat function bypass the heat pump heat mode all together? What about programmable electronic thermostats? Can they complicate the testing of E-heat in hot weather?

I know I should know this but I just want to be sure. If I can get an answer this time, I'll never have to ask it again.

I have been testing heat pumps in the heat mode during the summer for about 14 years, and I have not had a problem or damaged anything that I know of. Who said you should not turn the heat pump mode on during the summer or when it is warm?

The heat strips should override the heat pump mode when you turn the thermostat to the setting that calls for them. I would say that about 50% of the time I find that the heat strips are not working properly, as they are seldom used and the homeowners don't know about them.

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Carrier manuals posted in the thread below say do not run heat pump in heat mode above 66 degrees outside temperature.

https://www.inspectorsjournal.com/forum ... IC_ID=5666

I just wanted to make sure that selecting emergency back up heat mode would bypass the heat pump function. You have confirmed that much Scott, so thank you. [^]

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I hate to differ with Scott being that he's such a great source of info, but....

Without digging into my archives for documentation everything that I've ever come across says not to use heat pump in heating mode during warmer temps and the 66 degrees that John referenced sounds about right. In the inspection you either run them to cool or to heat - not both. With the exception of the reversing valve's operation, if the unit heats then it will cool and vice versa.

The emergency heat mode will bypass the heat pump and only run the secondary system.

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Ditto to what Eric says. I typically use 62 degs as my cutoff for heat/cool with heat pumps. Some manufactures use 60 degs for A/C and HPs, some use 65 degs or 66 degs. I choose 62 since its in the middle.

I also do NOT run backup heat mode when the outside temp is above 62 degs. I note in my report that I could only test the HP in cool mode due to outside temp and the HP's heating function (including operation of the backup or auxiliary heat) was not tested. I further explain that by doing so (running HP in heat mode above 62 degs), damage could occur to the system.

I did once get a call from a client 6 months after the home inspection stating that the HVAC just left the house and he determined that there was no backup heat installed in their HP. I asked her to read her report to me in the Heating section and I clearly stated what I mentioned above.

About all I do in the cooling months regarding HPs in heat mode, however, is verify that there is a "Em Heat" or other similar notation on the thermostat indicating there is a backup source installed. Lately, I have seen several instances of new thermostats installed that did not indicate any "EM Heat" option. I opined that the installed thermostat may not be designed to run a HP.

Also, seeing if there are some large rated breakers on the air handler or breaker panel (and labeled for HP) can help indicate the presence of backup heat source.

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That isn't correct. If you turn the heat pump off, manipulate the thermostat to as cool as possible, switch it to emergency heat, and then crank the thermostat, the condenser is locked out and it can't be damaged.

You're essentially operating an electrical furnace and there's no way that will damage the system.

Eric was right. What you don't want to do in the summer is set a heat pump to "heat" mode, and then crank up the temperature. That will engage the condenser and you CAN risk damage to it.

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Matthew,

I don't have a picture handy but there are new digital thermostats designed to run a heat pump that have no readily visible emergency heat selection.

You have to push and hold a couple of the buttons at the same time to get it to switch to emergency heat.

Don't even remember the brand.

BUT, it's a small white square with a digital screen and only a couple of buttons like up - down temp and fan auto - on.

Haven't seen one in awhile but I think I remember that you push and hold the up and fan mode buttons for a few seconds to get it to switch to emergency heat.

Might want to look at that. White - Rodgers brand rings a bell but I'm not sure.

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Originally posted by John Dirks Jr

I know you should not run a heat pump in the heat mode during hot weather.

Every manufacturer that I've heard of instructs you not to run the heat pump when it's warm out. That said, like Scott, I've been running heat pumps in the heating mode in warm weather for 16 years without a problem. I've never seen or heard of a heat pump being damaged by running in the heating mode during warm weather. I suppose that, in theory, the system could develop high head pressures and be damaged but, in most systems, the safety will cut in a shut down the compressor before anything bad happens.

What about the emergency electric coil? Is it safe to command that in hot weather?

Yes. It's perfectly safe to run just the electric coils in hot weather.

Will the thermostat E heat function bypass the heat pump heat mode all together?

If the stat has an emergency setting, yes, it will bypass the heat pump.

What about programmable electronic thermostats? Can they complicate the testing of E-heat in hot weather?

Not really.

- Jim Katen, Oregon

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  • 5 months later...

Simple. Check this out.

You are saying not to run a heat pump above the temp of 65 degrees. Why? You did post some instructions and a link. I read them. It's a typo, they are wrong.

The whole idea of a heat pump is to save money heating the home. What you are saying is that when the temp gets to be 65 the heat pump will shut off and the electric heat will turn on. So now our efficient heat pump is not given the opportunity to work because the condenser coil (inside coil in winter) can't dissipate the heat? Nope, no way.

The auxiliary heat, back up heat and emergency heat are all the same thing. You have no emergency heat coil and a back up heat coil they are one in the same. The only time the back up heat will come on automatically is when it gets to cold outside making it difficult for the outside coil to extract heat from the air. So the heat pump runs and runs and runs until the thermostat temp actually falls about .5 to 1.5 degrees. That signals the second stage bulb to drop (Old type stats) or in a digital the 2nd stage sensor. This turns on the auxiliary heat. This auxiliary heat can or could be staged to come on. For the most part it all comes on at once, 10kw or 15kw. Most systems have 10 kw installed that will usually work well with a 2.5 ton system. Anyways the electric heat comes on. Yes this is the same heat that is the back up heat, auxiliary heat and emergency heat.

It now will warm the air up in the plenum and duct system and into the house. This heats the home and will satisfy the thermostat and the system will shut down. If its cold out the heat pump just may seem to always run and the electric heat will come on and off as the second stage bulb dictates.

That explains the auxiliary heat. The emergency heat comes on when you manually move the lever on the stat to emergency heat. this will not allow the outdoor unit to run at all. The only thing that will be operating is the resistance heat (all of it) looks like a hair dryer going full tilt.

Another thing to know. We have all seen the ice on the outdoor unit in the winter before. So heat pumps have a defrost cycle to melt this ice. It is done by the reversing valve many of you have mentioned. It puts the system into a/c mode. It will now let the outdoor unit be the condenser to throw that heat from inside the house to the outside. It does this only for a short time. While this is going on (a/c blowing in the house in Feb) the resistance heaters are again turned on to over power the cold air that is coming out of the supply vents. So you never really know that a/c is on.

It makes no sense that if it is 65 degrees outside the unit will only activate the resistance heaters. No units have controls for that. That is the birth of dual fuel, or better know as hybrid systems. They are heat pumps over top of a fossil fuel heat source. When it's to cold for the heat pump to work the furnace is activated. When its warmer outside and the heat pump has good weather to extract heat from, the heat pump comes on. Thats the latest craze in the recent fuel hikes.

So what your saying a heat pump only works when its not to cold and not to warm? So that would mean it works from 20-25 to 65 degrees? Nope. Look at it this way. If what you say is true everyones electric bill would be sky high. Everyone with a heat pump would be running resistance heat from 65 degrees up to the typical set point of 70. Everywhere! Not gonna happen. Their is NO control in any heat pump to shut it off at 65 and just let the resistance heat work. You just shot the whole SEER & COP rating system in the leg. My ultra high efficiency system just became a dog if I'm relying on the most expensive type of heat one can buy to heat my house from 60 to 70.

I will post a good way to test a heat pump this week if you guys want.

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Originally posted by energy star

Simple. Check this out.

You are saying not to run a heat pump above the temp of 65 degrees. Why? You did post some instructions and a link. I read them. It's a typo, they are wrong.

Um, no, they're not all wrong. Most, if not all, manufacturers instruct you not to run the heat pump in heating mode when it's warm out. Sure, there's little danger of anything bad happening, but the manuals are written that way on purpose. It's not a typo.

And by the way, while 65 degrees is a very conservative cut off point, the warmer it is outside, the greater the risk that the system will go off on high head. You can't change the size of the coils and they weren't meant to carry that much heat.

The whole idea of a heat pump is to save money heating the home. What you are saying is that when the temp gets to be 65 the heat pump will shut off and the electric heat will turn on.

I just reread the whole thread and no one's said that. What they're saying is that the MANUFACTURER warns against running the heat pump when it's warm outside - no one's claiming that the system will energize the heat strips when its warm out. I suppose that the manufacturer is assuming that people wouldn't want to heat their homes when it's warm out.

So now our efficient heat pump is not given the opportunity to work because the condenser coil (inside coil in winter) can't dissipate the heat? Nope, no way.

No one here said that.

The auxiliary heat, back up heat and emergency heat are all the same thing.

I think that most everyone here knows that.

You have no emergency heat coil and a back up heat coil they are one in the same.

No one here said they were.

The only time the back up heat will come on automatically is when it gets to cold outside making it difficult for the outside coil to extract heat from the air. So the heat pump runs and runs and runs until the thermostat temp actually falls about .5 to 1.5 degrees. That signals the second stage bulb to drop (Old type stats) or in a digital the 2nd stage sensor. This turns on the auxiliary heat. This auxiliary heat can or could be staged to come on. For the most part it all comes on at once, 10kw or 15kw. Most systems have 10 kw installed that will usually work well with a 2.5 ton system. Anyways the electric heat comes on. Yes this is the same heat that is the back up heat, auxiliary heat and emergency heat.

It now will warm the air up in the plenum and duct system and into the house. This heats the home and will satisfy the thermostat and the system will shut down. If its cold out the heat pump just may seem to always run and the electric heat will come on and off as the second stage bulb dictates.

That explains the auxiliary heat. The emergency heat comes on when you manually move the lever on the stat to emergency heat. this will not allow the outdoor unit to run at all. The only thing that will be operating is the resistance heat (all of it) looks like a hair dryer going full tilt.

Good explanation.

Another thing to know. We have all seen the ice on the outdoor unit in the winter before. So heat pumps have a defrost cycle to melt this ice. It is done by the reversing valve many of you have mentioned. It puts the system into a/c mode. It will now let the outdoor unit be the condenser to throw that heat from inside the house to the outside. It does this only for a short time. While this is going on (a/c blowing in the house in Feb) the resistance heaters are again turned on to over power the cold air that is coming out of the supply vents. So you never really know that a/c is on.

Another good explanation. But I have one quibble. In my part of the country, the defrost mode works great if there's frost on the coil, but not ice. If you've got ice, the defrost mode just melts some of it and then it re-freezes into a larger block. Ice on an outdoor coil means that there's a bigger problem than the defrost cycle can deal with.

It makes no sense that if it is 65 degrees outside the unit will only activate the resistance heaters. No units have controls for that.

No one said that. You're imagining it.

That is the birth of dual fuel, or better know as hybrid systems. They are heat pumps over top of a fossil fuel heat source. When it's to cold for the heat pump to work the furnace is activated. When its warmer outside and the heat pump has good weather to extract heat from, the heat pump comes on. Thats the latest craze in the recent fuel hikes.

Those systems have been around for a long time. I agree that, in many cases, they don't make any economic sense. It depends on what your're paying for electricity vs. gas. I've only heard them termed "hybrid" in the last year or so. There's little doubt that the manufacturers are trying to capitalize on the hybrid car craze by co-opting the term.

So what your saying a heat pump only works when its not to cold and not to warm? So that would mean it works from 20-25 to 65 degrees? Nope. Look at it this way. If what you say is true everyones electric bill would be sky high. Everyone with a heat pump would be running resistance heat from 65 degrees up to the typical set point of 70. Everywhere! Not gonna happen. Their is NO control in any heat pump to shut it off at 65 and just let the resistance heat work. You just shot the whole SEER & COP rating system in the leg. My ultra high efficiency system just became a dog if I'm relying on the most expensive type of heat one can buy to heat my house from 60 to 70.

No .... one .... is .... saying .... that.

I will post a good way to test a heat pump this week if you guys want.

Please do.

- Jim Katen, Oregon

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Tell me then Jim, when its 65 degrees outside and my house t-stat is set at 70, and my inside temp falls to 69, what form of heat is going to kick on to bring it up to set point with a heat pump?

If you have ice on the coil, you need to adjust the defrost timer to check for defrost more often. You can change that.

Yeah I know all about "it may be low on freon". Still, the defrost time could be changed to occur more often.

Also, "hybrid" is a new word for "Dual fuel" that has been around a while, means the same thing.

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Originally posted by energy star

Tell me then Jim, when its 65 degrees outside and my house t-stat is set at 70, and my inside temp falls to 69, what form of heat is going to kick on to bring it up to set point with a heat pump?

But you're sort of drifting starboard of the point. The 65 degrees--or 66 according to Carrier's manuals--is an arbitrary figure. It could just as easily be 60 degrees or 70 degrees, but the industry has settled upon a standard of 65.

More importantly, that standard is pretty much moot for us that work in hot climates. What do you think happens in a system operating on heat mode when the exterior ambient is 95 degrees, like it often is here in July and August? And what if a system fails--for whatever reason--and a seller is told we operated her heat pump in violation of the manufacturer's instructions? I pasted a post from another thread below. Do you agree or disagree?

"After great conversation with the retired owner of a Carrier dealership I stand corrected.

As Jim had mentioned, the condenser surface area is much larger than the evaporator so, in the heating mode it is capable of extracting more heat than the evaporator is able to reject. High head pressure is the result. I had thought that the evaporator, being multi pass, would be able to keep up. Wrong.

He said that while starting it to make sure the reversing valve worked wouldn’t do any harm running it for too long could result in damage.

Moral of the story: If you stray from manufactures recommendations you are on your own.

Terry

http://www.hlis.net"

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Morning. Yes thanks for showing that post. I wanted to show Jim that because he made mention of my remark to that claim.

Before I tell you if I agree or Disagree, let me remind us all how this post started. It was a question about testing a heat pump.

Many said a heat pump can't be tested if the temp is above 65. This is wrong. Way wrong. You can turn a heat pump on at 65, 66,67,68,69,70. You will not damage one thing. Yes you will be running a higher head pressure but no where near the designed limits of that cut off. You will hurt nothing. So from an inspection standpoint I would turn on a heat pump simply to test in almost all conditions.

My answer:

I disagree with your buddy. Both coils are matched to work with each other. The R&D team made sure of that.

Like I asked, if it is 68 outside and my stat is set to 70, and then my temp falls to 69 or a tad lower, what heat will kick on to satisfy my stat at the 70 degree set point?

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If I come home after an extended period of time when I've left my thermostat down to conserve energy and it is 65 F in and out, I turn the t-stat to 75 and the heat pump better run continuously til it reaches the demanded 75. This takes an extended period of time even with the heat strip energized, which it will be until about 73. (Maybe about the time it takes to do a home inspection.) I don't think it is an unreasonable request. I'm sure this is done in a large percentage of homes across the country. Often times I will adjust my t-stat incrementally to avoid the resistant heat as much as possible. (I know sometimes I can be real tight wad.) I say test em.

Energy star, I would like to see your test method.

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Originally posted by energy star

Morning. Yes thanks for showing that post. I wanted to show Jim that because he made mention of my remark to that claim.

Before I tell you if I agree or Disagree, let me remind us all how this post started. It was a question about testing a heat pump.

Many said a heat pump can't be tested if the temp is above 65. This is wrong. Way wrong. You can turn a heat pump on at 65, 66,67,68,69,70. You will not damage one thing. Yes you will be running a higher head pressure but no where near the designed limits of that cut off. You will hurt nothing. So from an inspection standpoint I would turn on a heat pump simply to test in almost all conditions.

My answer:

I disagree with your buddy. Both coils are matched to work with each other. The R&D team made sure of that.

Like I asked, if it is 68 outside and my stat is set to 70, and then my temp falls to 69 or a tad lower, what heat will kick on to satisfy my stat at the 70 degree set point?

It's not a matter of the coils being matched, they are (assuming it was installed correctly, no retrofits improperly installed etc). It's a matter of total heat of rejection.

As stated before, the surface area of the condenser is much greater than the surface area of the evaporator. The amount of heat that the condenser will pull from the air, in the heat pump mode with high ambient temperatures, is more then the evaporator can reject which will cause high head.

Now, will it be a problem at 65, 70 or 75° F - probably not. If we shift the outdoor temperatures though and use 90° F as an outdoor ambient can we run the heat pump, in the heat pump mode, with out any problems - no. It will most certainly cause a high head condition. However at 90° outdoor ambient can we run the heat pump in an air conditioning mode - yes. It's not a matter of the coils being matched. It's about surface area and heat of rejection.

Having said that though we, as home inspectors, need to default to the recommendations of manufactures. It's defensible.

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Originally posted by energy star

Tell me then Jim, when its 65 degrees outside and my house t-stat is set at 70, and my inside temp falls to 69, what form of heat is going to kick on to bring it up to set point with a heat pump?

The heat pump, of course. But that wasn't the question.

The question was about the propriety of a home inspector running a system in a manner that is contrary to the manufacturer's instructions. Every inspector has to make this decision by himself. He has to take into account the risk of doing so vs. the benefit to his customer. He does this by gathering useful information including the experiences of other inspectors and the requirements of the manufacturer's installation instructions. He can then decide how to proceed at whatever risk level he's comfortable with.

I agree with you that the manufacturers' instructions seem to be excessively conservative but they are what they are and John should take that into consideration when deciding on his inspection protocol. Telling him that it's a typo is not helpful.

I run the heat pump when it's over 66 degrees all the time. But I have a high threshold for risk. John may not. It's up to him to make that decision, not be bullied into it.

If you have ice on the coil, you need to adjust the defrost timer to check for defrost more often. You can change that.

Yeah I know all about "it may be low on freon". Still, the defrost time could be changed to occur more often.

Of course. My point was that, if there's actual ice on the coil, the defrost cycle won't usually get rid of it.

Also, "hybrid" is a new word for "Dual fuel" that has been around a while, means the same thing.

Yes, I know. My house has such a system that I installed in 1992. My point is that the hybird label is an attempt to co-op a trendy word.

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Yes the heat pump of course. Do you not see that the manufactures instruction booklet is contradicting itself?

Say its 68 outside and my t-stat is set at 70. My temp in the home slowly drops to 69. The heat pump will automatically come on in the heat pump mode!

So why is a system designed and engineered by the manufacturerid="blue"> to come on and off all day long with no resistance heat at or above the 65 degree mark to satisfy my 70 degree set point in those same instructions?

To Terrance,

''As stated before, the surface area of the condenser is much greater than the surface area of the evaporator. The amount of heat that the condenser will pull from the air, in the heat pump mode with high ambient temperatures, is more then the evaporator can reject which will cause high head.''

The air handler fan moves way more air across its coil and at a faster rate than the fan in the OD unit. The each have a different fan blade.

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