Heat pump questions - indoor & outdoor thermostats

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Old 11-10-08, 10:21 AM
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Heat pump questions - indoor & outdoor thermostats

Hello,

A few years ago, I bought a 30-yr-old house. It's got a Heil heat pump (cooling and heating w/aux electric heat) that I think may be as old as the house. The thermostat (an old-fashioned Mammoth-brand rectangular box with levers) only provides the heat/off/cool and auto-on fan options.

I'm trying to update the system to make it more comfortable (a fairly constant 70 degrees) when it's below 40-45 degrees outside. (ie, get the aux heat to come on when the heat pump can't do the job alone). I'm also trying to keep it as energy efficient as possible.

Right now, the temp on the stat will move up to only 70 and it feels much cooler than that. If I turn the stat up, the aux will kick in for a little while and blow warm air. It'll then cut off, or at least it seems like it has) and the heat pump just runs and runs without the house ever feeling warmer.

I'm going to clean (or have someone else clean) the condenser and everything else. But I'm also thinking I should replace the stat with a programmable one that will also allow me to control the aux heat. And I'm wondering if an outdoor stat is called for.

I've been reading about heat pumps and thermostats online, but I still have these questions:

1) Can an outdoor stat be installed on an older system? If so, do you think it's a good idea in this case?

2) Without an outdoor stat, would a new indoor stat allow me to bypass the heat pump and go directly to aux? Or would it be more energy efficient to allow the heat pump to continue to run even when it doesn't seem to be doing much good? (Is it still having some effect, even tho minor, on the temp?)

3) I've read that if the heat pump shuts down when the outside temp is low, it should be kept off for several hours, then turned back on in the cooling mode until the coolant warms back up. Otherwise, it can damage the valves. Is this true? If so, and people are using an outside stat to control the heat pump, aren't they risking damage?

4) I'd like to get a Honeywell stat (for inside) because I'm told they're reliable. But I'm confused by all the models available. (In this small city, I can only locate the TH6220D and TH7400D.) I'd like the simplest programmable version that also allows the most control over the heat pump/aux action. Can you recommend one?

I think that's it for now. Thank you for all your help. You folks are great!
 
  #2  
Old 11-10-08, 02:03 PM
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Well first Id say .Is the out door coil clean ??? the indoor coil clean??? filters. the blower blades clean also??? when was the last time the freon was checked??? Is it OK???
Now as to stats lot of them out there how much do you want to spend. Any of them that say for heat pump are ok. Also any of them or your old one if you go to AUX heat the pump dont come on . You can go back and run the out door unit any time its ok. Why would you want a out door stat?? that could screw up the unit from going into defrost I think.
 
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Old 11-10-08, 06:42 PM
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Thank you, Ed. I appreciate your input. I change the filter regularly, and I'm going to have everything cleaned this week (including the outdoor coil as long as we have a warm enough day).

My existing stat doesn't have an aux setting, hence part of the reason I think I need to replace it. (I'd also like one that's programmable.) Just wondering if the lower priced Honeywell programmable models that work with heat pumps all include an aux setting, or if the less expensive ones are like what I have now (one setting for heat and one for cool). Maybe I need to contact Honeywell directly. It's too hard to tell from what's available in online ads.

And I really don't know about the outdoor stat. I just know I've seen other online forums in which people discuss their use. I just wonder if they're actually a good idea or if, like you suggested, they could cause damage.
 
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Old 11-10-08, 06:49 PM
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One other thing... I have not had the freon checked. But a repairman I spoke with told me it's very difficult to get an accurate reading once the weather turns cold. I had plenty of cool air when running the A/C this summer, so I'm hoping that's not the problem.

By the way, tonight the aux heat seems to be running more (warm air coming from the vents), maybe because it's colder tonight (31 deg). And the heat pump is actually shutting off now and then, tho only for a very short time. We have the stat set at 75 but the temp reading on the stat never goes above 68 or so.

I'm hoping the new stat and cleaning will help a lot. But I'm still wondering about the outdoor stat and best indoor stat. Thank you again.
 
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Old 11-10-08, 10:53 PM
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>>3) I've read that if the heat pump shuts down when the outside temp is low, it should be kept off for several hours, then turned back on in the cooling mode until the coolant warms back up. Otherwise, it can damage the valves. Is this true? If so, and people are using an outside stat to control the heat pump, aren't they risking damage?

I've never heard the part about starting the heat pump in A/C mode, but it is true that if you cut power (turn off the circuit breaker) to your heat pump or lose electricity for more than a couple of hours you should wait at least 8 hours before restarting it. My heat pump is 3 years old and has a sump heater to keep the compressor warm all the time. It makes no difference if my heat pump runs or not as long as it has power the compressor stays warm. Because of the age of yours it may not have one.

>>1) Can an outdoor stat be installed on an older system? If so, do you think it's a good idea in this case?

I would think that installing and outdoor temp sensor has nothing to do with the heat pump (unless yours is actually dependent on running periodically to prevent it from freezing) I have an outdoor temperature sensor and I really like it. I can set the low cutoff point for my heat pump with it.

>>2) Without an outdoor stat, would a new indoor stat allow me to bypass the heat pump and go directly to aux? Or would it be more energy efficient to allow the heat pump to continue to run even when it doesn't seem to be doing much good? (Is it still having some effect, even tho minor, on the temp?)

All tstats that I know of that are heat pump capable let you put the system into aux or emergency mode bypassing the heat pump and then relying on just the heat strips. All heat pumps reach a point where it gets so cold outside that they are not saving you money anymore.

-doug
 
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Old 11-11-08, 08:36 AM
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Originally Posted by LauraM View Post
1) Can an outdoor stat be installed on an older system? If so, do you think it's a good idea in this case?
By outdoor stat, do you mean a tstat that has an outdoor sensor that ties to your indoor tstat? I think that's what you mean, but just want to clarify.

Originally Posted by LauraM View Post
2) Without an outdoor stat, would a new indoor stat allow me to bypass the heat pump and go directly to aux? Or would it be more energy efficient to allow the heat pump to continue to run even when it doesn't seem to be doing much good? (Is it still having some effect, even tho minor, on the temp?)
With an outdoor sensor and a more advanced tstat you can lockout the HP and aux heat below and above certain outdoor temps respectively. Until you get to very low temps it is generally more economically advantageous to run the HP over just heat strips because an HP has higher efficiency. Based on your setup I'm guess you don't live in a moderate climate where you don't see temps below 0. I'm sure you've noticed that as the outdoor temps drop the heat produced (per design) is less, and at some point it becomes lower than your body temp causing some comfort issues. Even at low temps where the supply air feels cool, and its not supplying all your heating needs, an HP is still more efficient than heat strips.

Originally Posted by LauraM View Post


3) I've read that if the heat pump shuts down when the outside temp is low, it should be kept off for several hours, then turned back on in the cooling mode until the coolant warms back up. Otherwise, it can damage the valves. Is this true? If so, and people are using an outside stat to control the heat pump, aren't they risking damage?
The concern is damage to the compressor. 5 minutes should do it and that may be more time than needed depending. In fact many HPs and tstats have a safety built in to prevent it from restarting.

Originally Posted by LauraM View Post


4) I'd like to get a Honeywell stat (for inside) because I'm told they're reliable. But I'm confused by all the models available. (In this small city, I can only locate the TH6220D and TH7400D.) I'd like the simplest programmable version that also allows the most control over the heat pump/aux action. Can you recommend one?
Any tstat you get should do fine that can control an HP with aux heat, and I believe both do. Looking at the installation guides neither of the Honeywell tstats you've listed accept an outdoor sensor.
 
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Old 11-11-08, 08:43 AM
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Originally Posted by LauraM View Post
One other thing... I have not had the freon checked. But a repairman I spoke with told me it's very difficult to get an accurate reading once the weather turns cold. I had plenty of cool air when running the A/C this summer, so I'm hoping that's not the problem.

By the way, tonight the aux heat seems to be running more (warm air coming from the vents), maybe because it's colder tonight (31 deg). And the heat pump is actually shutting off now and then, tho only for a very short time. We have the stat set at 75 but the temp reading on the stat never goes above 68 or so.

I'm hoping the new stat and cleaning will help a lot. But I'm still wondering about the outdoor stat and best indoor stat. Thank you again.
I'm not sure it is correct that you cannot check charge at lower temps. Howerver, if in cooling mode its meeting capacity I would guess your charge is correct, or close to it.

If you're current setup is not meeting your tstat then you need a bigger HP or larger heat strips or a combination of both. There may also be some changes to your ductwork that can provide better comfort. Depending on your locale your ductwork may be optimized for cooling rather than heating, or vice versa.
 
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Old 11-24-08, 11:34 AM
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Laura, some HP models do have the capability to add an optional outdoor tstat in order to lockout aux heat over about 40 degrees. So it depends on your unit. If you open the electrical cover on the heat pump there is usually a wiring diagram in there that will tell you if this is an option.

The other way you can do this is to buy a good indoor tstat like the honeywell IAQ or others that have an option to hook in an outdoor tstat and control the aux lockout from there.

If you want more comfort and ability to lower your setpoint think about getting a humidifier for the cold weather. I highly recommend them.

Lastly, if you want hotter air from your HP you can install a fan control unit like the ICM CC750 - works great and will also give you better dehumidification in the summer.
 
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Old 12-01-08, 04:07 PM
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heatpump crossover

i have installed a heatpump with a gas furnace. bought a ICM IC-5812 programable digital dual fuel stat. i had my heatpump running down to 25 degrees b4 it would cross over to gas. however i find that it never shuts off and does not heat the home well. the problem i have is my house is 100 years old it is not insulated so i now have my heatpump set to cross over to gas at 40 degrees. 40 and above it will heat the house as hot as you could want it. it has an outdoor sensor that runs to the thermostat and automatically locks out the heatpump. on a new house well insulated ive set the cross over from heatpump to gas at 16 degrees and they have no problems heating the home down to that brisk temperature.
 
  #10  
Old 12-02-08, 07:12 AM
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That's actually a comfort crossover point

Originally Posted by w0ahh View Post
i have installed a heatpump with a gas furnace. bought a ICM IC-5812 programable digital dual fuel stat. i had my heatpump running down to 25 degrees b4 it would cross over to gas. however i find that it never shuts off and does not heat the home well. the problem i have is my house is 100 years old it is not insulated so i now have my heatpump set to cross over to gas at 40 degrees. 40 and above it will heat the house as hot as you could want it. it has an outdoor sensor that runs to the thermostat and automatically locks out the heatpump. on a new house well insulated ive set the cross over from heatpump to gas at 16 degrees and they have no problems heating the home down to that brisk temperature.
There are two types of crossover/balance points: comfort and economic.

Comfort crossover happens when the air drops below our skin temp and begins to feel cool and drafty. This is a somewhat personal and subjective. It is partly due to the lower BTU output but same blower speed. New systems with VS blowers and Hot Heat Pump mode do help here.

Economic crossover, or cheapskate crossover , happens when the per BTU cost of your aux is the same or cheaper to run then the HP. Often there is a temp above the economic crossover where the HP cannot supply all your heating needs, but what little it does run is still saving you $$$. Any dual fuel tstat should bring on the aux when the HP cannot keep up, unless you've locked out the HP at the tstat or on the HP.

Typically the comfort balance point is much higher than the economic balance point. Your HP's duty cycle doesn't really matter so long as its providing comfort and/or savings - whatever your goal is. Its duty cycle might have an impact on longevity, but that's a different and somewhat controversial issue.
 
  #11  
Old 12-06-08, 12:08 AM
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Just a note. I have a Goodman heat pump. Bought a new RiteTemp programmable thermostat.......Couldn't figger out how to wire it. Went to the RiteTemp site and Goodman was not on their list......Found out it was Amana....Wired up like it was Amana and it works perfect. Some guy I know had the same prob and he was charged 200 bucks to wire a simple thermo......I wonder if there's a scam going on?......I just joined tonight...Just wish I found this forum years ago.....L
 
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Old 12-06-08, 08:42 PM
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hairy hairy hairy you sound like a conspiracy theorist.
 
 

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