Heat Pump vs aux propane heat

I live in Southern Maryland. This year we had a heat pump installed with propane backup heat. Early on we were using a lot of propane because I was turning the heat down to 55 at night. I have rectified this by setting the heat to 68 when we are home and 66 when we are away or asleep. Is 2 degrees the most I should fluctuate it on a daily basis?
Secondly and this is my main question... I have heard that heat pumps are no longer efficient at 30 degrees. So when I see a stretch of a few days that are going to be cold, below 30 degrees, should I just turn on emergency heat? Thus turning off the heat pump for these cold days when it would be inefficient? Currently it tries until it can't keep up. I am thinking this time when it trying it is just burning my electricity and cash. Would this be the most efficient way to heat?
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I wouldn't fluctuate it at all without a special programmed themostat designed to prevent backup heat going on when exiting setback cycle.
You ask an interesting question about heatpumps. I would presume that the controls for the heatpumps are designed to be smart enuf that you don't have to worry about bypassing the heatpump. The bypass is for if the heatpump is broken.

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My thermostat is very fancy with all the whistles and bells. Not sure if it tries not to use auxiliary heat or not but it does figure out when to come on to have the house to the desired temp at a given time.
The thermostat also has options for exterior thermometer to help it decide when to skip straight to aux heat. We do not have the exterior thermometer. If I had any idea what to install and how to install it I would. The heat pump itself may have equipment and the programming to realize the cold temperature and skip straight to aux heat but I have not read this anywhere.
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Right. A heat pump control system is designed to switch over to backup heat when it makes economic sense to do so [+].
It's a balance between HP/outside temperature efficiency and cost per BTUs in the backup system.
If it was installed/adjusted correctly and is operating properly, don't second guess the control system, it'll do a much more effective job at minimizing cost than you can erratically flipping a switch. Even if the propane cost has shifted around a bit.
In other words, leave it in auto, unless the control system (or HP) is outright failing and can't keep your house warm.
[+] The other time a HP switches to backup heat is if the inside temperature is "too far" away from the thermostat set-point. The threshold for "too far" is usually something on the order of 3-5 degrees. The control circuitry figures that the HP is unable to keep up if the temperature difference is too high, and switches on emergency heat to catch up. This makes particular sense when you realize that a HP can't produce as many BTUs per hour as a straight gas furnace.
So, if you open all the doors and windows during a blizzard, the control system automatically notices the gross temperature difference, and switches on backup to try and get the temperature back in the comfort range as soon as possible.
The difficulty arises with setback thermostats. They cause large abrupt changes in the T-stat setting. "Oops, we can't keep up, switch on the backup!". You need to use special programmable thermostats that either bring up the temperature slowly (within the HP's ability to keep up - some of these T-stats have programmable ramp-up rates I think), or inhibit backup heat during a catchup interval.
--
Chris Lewis, Una confibula non set est
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If it hasn't been done already, you should have had an outdoor thermostat installed that automatically switches over to propane when it gets down to a certain temperatrure. SMECO recommends 35 degrees but I have seen it set as low as 28 and as high as 42. Depends on your comfort. Who installed your system? T.N. Bowes? Or did one of the propane companies install it?
I have a mnaual switch for the aux heat (on my heat pump) and I only turn it on when the temps get down in the low 20s. I have no backup other than the "heat strips" (aux heat) and my heats fine. My electric bill still does not match what I was spending on oil.
I'm moving if SMECO raises the damn rates again......
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you defenitly want to switch to backup when the heat pump has to use defrost cycles to melt ice off of the outdoor coils... generally around 32.
I switch over at 40 bacause I factor in the wear and tear on the poor compressor running its guts out ...
Mark
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Potter put my system in. I would be interested in an outdoor thermostat... should I contact Potter?
Also are you saying that because I set my thermostat low at night and aux heat is coming on to bring it up to temp in the morning there is a problem with my system? This is only a problem I had when I was setting the heat way back at night. If this is a tell tail to a real problem I want to get it fixed now!
Thanks for the replies!
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Let me clear up one thing: I think when you were originally talking about an outdoor thermostat, you were talking about an out door sensor so that you could read the outdoor temperature on your indoor thermostat. The thermostat I am talking about is one that will automatically bring on your backup (propane furnace) when the outdoor temperature drops to 'X' (wherever you set it). They MAY have put a fossil fuel kit on the system, but it sounds like they did not.
You might want to call Potter and ask if they could "install something that will shut off the heatpump at a given temperature and turn on the furnace".
Just a guess: Your system is made by Carrier and you buy your propane from Suburban and you live in Waldorf?

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The system is York. Our propane supplier is Southern Maryland Gas. The only one that does not have a minimum purchase. And you are correct we do live in Waldorf. I will check about a fossil fuel kit.
Thanks!
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YORK??!!! YUK!!!
;-]
It doesn't have to be a fossil fuel kit, though it works the same way. The way I equate it:
Outdoor thermostat and a bonnet switch: $125 in parts. Fossil fuel kit: $300-$400 to do the same thing.
YMMV.......
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Potter put my system in. I would be interested in an outdoor thermostat... should I contact Potter?
Also are you saying that because I set my thermostat low at night and aux heat is coming on to bring it up to temp in the morning there is a problem with my system? This is only a problem I had when I was setting the heat way back at night. If this is a tell tail to a real problem I want to get it fixed now!
Thanks for the replies!
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Interesting argument- that you used a lot of propane because of night-time setback. If one follows from the other, something in between is totally hosed, and is the cause. Or something totally separate is screwed up. Like- leak, erroneous meter reading, whatever.
J
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snipped-for-privacy@sme-online.com wrote:

Night setback tends to kick in the backup for two reasons. First consider when the set back is likely to be canceled. Usually in the morning at the coldest part of the day. Far more likely to kick in if for no other reason that it is not too cold outside. I don't know about their control systems, but I would not be surprised if they detected the difference between the set temp and the current temp and would decide that it was going to need to kick in the backup source to help bring up the temperature in a reasonable amount of time.
--
Joseph Meehan

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Joseph Meehan wrote: <snip>

Especially if the OP was setting back the thermostat ~13 degrees at night as could be inferred from his post. No way a heat pump is going to recover from that on a cold night without some help.
I almost feel like I am using too little gas with my heat pump. I live in NC and have used a whopping 6 cf this year, since the gas backup on the downstairs heat pump is the only gas appliance. With the base charges it works out to about $11/cf :( Don't know why they only installed gas on first floor and no gas water heater or stove when they built the place, although I guess it was the cheapest way for the builder to be able to claim "gas heat".
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On 15 Feb 2006 09:23:36 -0800, Brian Attwood wrote:

I have similar situation - the furnace is the only gas (propane) appliance. I did that because I wanted a gas furnace, but the local EMC gave me a $1000 rebate, a free underground drop of >700 ft w/transformer by house, and a free 50 gal Marathon water heater (lists as $693.50 at Granger) for going total electric (dual fuel counts as total electric for their purposes). Maybe the builder got a similar package. Since the only gas appliance I really wanted was the furnace, I got my cake and ate it too :-)
Later, Mike (substitute strickland in the obvious location to reply directly) ----------------------------------- snipped-for-privacy@bellsouth.net
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My heat pump run at 17 degs, and then the Natural gas furnace takes over, I do get a reduced electric rate in the winter because of the heat pump, so I let it run till it can't keep up. The installer should of set the outside unit to run down below 30 degs, or to where its not keep you comfortable.
Tom \\

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In 1978 my new home included a GE (now Trane) high (for those days) efficiency heat pump. The home was located 8 miles west of Atlantic City. NJ had a moratorium on new connections for gas as was in short supply.
At the time I was taking a job as a generation performance engineer for the local electric utility. I confirmed (I'm a mechanical engineer (PE)) the capacity rating of the heat pump vs the heating load calculation. I also had the company's heat pump engineer check it also. The heat pump could carry the house down to 15 degrees without backup heat.
18 years later we moved and sold the house. The original heat pump was still running well. Total repairs during that 18 year period was NOTHING.
I suggest that you just confirm what the manufacturer suggests is the appropriate balance point setting and leave the controls to do their job.
Low outside temperatures do reduce the COP (coeefficient of performance) and do reduce the temperature of the air handler output. Those two items may cause some people to want to use backup heat, but why try and second guess the manufacturer?
twfsa wrote:

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On 14 Feb 2006 07:41:48 -0800, Home owner wrote:

Have same setup here - NW GA. My heat pump has a thermostat in it's cabinet that turns the propane furnace on at whatever temperature it is set to. Mine is located underneath the service panel on the heat pump in a box about 8 inches square, there is a temperature probe exiting the box. Inside the box is a knob which has temperatures marked around it - you just turn the knob to the temperature you want the heat pump turned off. Pretty simple to change and not too hard to find - at least on my unit. BTW, make sure the bulb on the probe isn't mounted so that the sun shines on it for proper operation.
My system also has a plenum sensor that detects when the heat pump goes into defrost and turns on the aux heat during defrost to prevent cold air coming from the returns. I don't know that this ever occurs with my outdoor thermostat setting of 35F, never noticed if it has.
Concerning the temperature setback on your thermostat. If you have an electronic thermostat, some (may be many) have a setting which will gradually raise the temperature from the lower setting to the higher setting gradually to prevent the auxillary heat coming on when the temperature outside does not warrant it. Some use a set amount of time per degree(s) others learn how long it takes to reach the desired temp and base calculations on that - I have no experience with the latter, only read about them. IIRC, mine had a switch to set before mounting the thermostat to do this. Your manual will tell you if the thermostat has this feature and what, if anything, needs to be done to activate the feature.
You should note that if you MANUALLY raise the temperature more than a few (dunno what it is offhand, but 5 comes to mind) degrees, the auxillary heat will come on regardless of the outdoor temperature. Since the change was done manually, the thermostat will not use the gradual method that is used for setback.

You should not need to manually change the thermostat setting to aux heat unless your heat pump isn't working or you want to use a portable generator to operate the furnace - most won't run a heat pump but will run a furnace since it is mostly just operating a fan. NOTE: Quite a few long-running and nasty threads have appeared in this group concerning the use of portable generators when the power is out and I won't go into any of that except to say that you should VERY THOROUGHLY RESEARCH THE ISSUE and FOLLOW APPROPRIATE SAFETY PRECAUTIONS AND PROCEDURES - nuff said and I won't respond to any comments regarding this issue.
As mentioned above, the outdoor thermostat should take care of those times that the temperature is low. The first thing I would do is check to see if there was some method of turning off the heat pump below a certain outdoor temperature installed in the system, if not, get one installed. If something is installed, it sounds like the cutoff temperature is set too low and needs to be adjusted up to whatever point you're comfortable with.
IIRC, I have read that there are some indoor thermostats that have a probe that runs outdoors which is used instead of the thermostat in the heat pump enclosure that I am familiar with. If you have one of these thermostats, you need to make sure that the probe is properly installed. This may be an optional item and the outdoor thermostat I'm familiar with may work fine with these thermostats also.
HTH.
Later, Mike (substitute strickland in the obvious location to reply directly) ----------------------------------- snipped-for-privacy@bellsouth.net
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