Heat Pump question...

[grsthegreat]

A heat pump is 3x as efficient as electric resistive heating. Try a clamp meter on your heat pump sometime. After the starting surge, mine draws about 9 amps to heat my entire house, and the system was sized before I upgraded all the doors and windows and insulation. It's 17 years old, and I'm sure I can downsize when I replace it.

The air handler has two 60 amp circuits for the heating strips, but since they don't come on I have never measured the draw. Assuming the code 80% load, that means the system goes from 2160 watts on the pump to 25,000 watts on the heat strips. It doesn't take much of that to ruin any savings that come from having a heat pump.

I have a 4.5 ton heat pump thats about 3 years old. Not counting starting surge, it runs at aprox 32 amps to heat my 4200 SF house. Since 2 cadet wall heaters will heat 2 rooms and use 20 amps , the heat pump is WAY better. It is a different kind of heat than wall heaters or gas..thats for sure. It feels slightly cool at the registers. But it will heat my house to whatever i set it at.
I have a Honeywell pro 8000 (had some letters before it....cant remember them though). You can set the set points when 2nd stage (back up emergency heat) will occur. Even if my house is at 62F, and the tstat adjusts to 68 by timer, the gas heater DOES NOT fire off. The thermostat has a learning mode that allows it to know when it needs to turn on to allow the house to be 68 at the set time.

Smarter than i am thats for sure.

 

[LD1]

I've previously owned two homes (in Virginia) with heat pumps, and IMHO they work better when left at one setting. I don't think you save anything by setting them back.

I disagree with this. I dont have a programmable t-stat, but I manually set min back at night. I believe it saves a good bit, and also keeps the aux. heat from being used as much.

Reason being...heat pumps looe efficency the colder it is outside. And it is usually colder at night:confused2: And in a well insulated house, the benefits are even better. In my house, my propane takes over @ anything below 17F outside. Where I live, MANY days it is mid 30's in the day, and mid teens @ night. I can keep my house @ 72-74 or so until the sun goes down. Then I set the t-stat back to 65-66 or so. Usually my house wont cool off enough to "call" for heat before the next day and the sun comes back up. Thus I dont have to use propane.

A heat pump is 3x as efficient as electric resistive heating.

True, but only to a point. The colder out it gets, that 3x's eff starts to drop. There WILL become a point in which the resistive heat would be more efficient. You heat pump could run 100% of the time, and not put out any heat at all if it is too cold outside. Plus the numerous defrost cycles it would have to go through.

I created a little spreadsheet to calculate my BTU output of my HP. Based on a 1000cfm blower, and the temps going into and out of the ductwork. Plus I know how many amps I am pulling. Propane is only a tad more efficient than resistive, and for my setup, 17 is the break even vs propane. 16 outside and the heatpump cannot deliver as much heat for the money. I imagine if I had resistive B/U, it would probabally be around 14-15 degrees.

 

[grsthegreat]

I disagree with this. I dont have a programmable t-stat, but I manually set min back at night. I believe it saves a good bit, and also keeps the aux. heat from being used as much.

Reason being...heat pumps looe efficency the colder it is outside. And it is usually colder at night:confused2: And in a well insulated house, the benefits are even better. In my house, my propane takes over @ anything below 17F outside. Where I live, MANY days it is mid 30's in the day, and mid teens @ night. I can keep my house @ 72-74 or so until the sun goes down. Then I set the t-stat back to 65-66 or so. Usually my house wont cool off enough to "call" for heat before the next day and the sun comes back up. Thus I dont have to use propane.



True, but only to a point. The colder out it gets, that 3x's eff starts to drop. There WILL become a point in which the resistive heat would be more efficient. You heat pump could run 100% of the time, and not put out any heat at all if it is too cold outside. Plus the numerous defrost cycles it would have to go through.

I created a little spreadsheet to calculate my BTU output of my HP. Based on a 1000cfm blower, and the temps going into and out of the ductwork. Plus I know how many amps I am pulling. Propane is only a tad more efficient than resistive, and for my setup, 17 is the break even vs propane. 16 outside and the heatpump cannot deliver as much heat for the money. I imagine if I had resistive B/U, it would probabally be around 14-15 degrees.

Mine is set thru the thermostat to switch into gas heat if outside temp reaches 20F (has a tstat near the outdoor unit).

 

[LD1]

Mine is set thru the thermostat to switch into gas heat if outside temp reaches 20F (has a tstat near the outdoor unit).

That is probabally a good setting for your HP. You could probabally sneak that a bit lower though. But it all depends on prices in your area and what your B/U heat is. If you have NAT gas, it is MUCH cheaper than propane, and the switch-over point would need to be set higher to be the most cost effective.

If you are like me, and have expensive BU, like resistive or propane, it is best to get all you can out of the HP. And mine is even a very old (15yr) unit with a low seer of 10:confused2:, and it is still more eff down to 17 vs propane.

The point I am making though, is that TOO many units are set up to switch over to propane @ 35-38 degrees. Which was fine 10 years or so ago when propane prices were under $1/gallon. But propane has went up MUCH more than electric (at least in my area).

I hear guys at work all the time complane about burning 500-600 gallons of propane in a winter. I always ask them what their HP is set @, and most of the time it is 35+. When I bought my house, first winter I used an entire 500 gallon tankfull. Since lowering the HP setting, I have cut that back to ~65 gallons for the whole winter. Sure, my electric bills are higher, but overall cost of heating is lower. It takes some figuring to determine what is best for each situation. But HP set @ 38 is 99% of the time, NOT the best.

 

[MossflowerWoods]

Sure getting to the right time of yr to be having this discussion.

Truth be told, no one on this end of the discussion can tell you what is wrong if anything with your system. Just too many variables.

Today's "T-Stats" are not you mom's and Dad's T-Stats. Higher end units only work with the mfgrs T-Stats. Mine is more of a dedicated computer and has a communication link with all connected components. From the controller I can look at what is connected, model and serial number. It tracks run time and cycles for each component. For transitioning between set points, depending upon temp difference it will start transitioning up to 45 min prior to set time for temp change. Can have up to 5 temp sensors in the house and can choose between which to use or take an avg of all connected sensors. I can also set the lock out point for when aux heat will come on. WHen aux heat is called for, my electric strips come on in stages and not all at once. Many other functions but are not relevant to this discussion.

You really do need to have a pro com out and give you a full assessment of your system and whether it is functioning to its ability.

My Tstat is NOWHERE NEAR that complex.

I need to break out the manual nd see if I can update some settings...
David

 

[clemsonfor]

That is probabally a good setting for your HP. You could probabally sneak that a bit lower though. But it all depends on prices in your area and what your B/U heat is. If you have NAT gas, it is MUCH cheaper than propane, and the switch-over point would need to be set higher to be the most cost effective.

If you are like me, and have expensive BU, like resistive or propane, it is best to get all you can out of the HP. And mine is even a very old (15yr) unit with a low seer of 10:confused2:, and it is still more eff down to 17 vs propane.

The point I am making though, is that TOO many units are set up to switch over to propane @ 35-38 degrees. Which was fine 10 years or so ago when propane prices were under $1/gallon. But propane has went up MUCH more than electric (at least in my area).

I hear guys at work all the time complane about burning 500-600 gallons of propane in a winter. I always ask them what their HP is set @, and most of the time it is 35+. When I bought my house, first winter I used an entire 500 gallon tankfull. Since lowering the HP setting, I have cut that back to ~65 gallons for the whole winter. Sure, my electric bills are higher, but overall cost of heating is lower. It takes some figuring to determine what is best for each situation. But HP set @ 38 is 99% of the time, NOT the best.

Yea my neighbor just had 100 gallons delivered and said it may last to the first of the year! He burns a wood stove too! And ill remind you i live in upstate SC. I asked why his propane backed up HP was even cutting on and he said somewhere in the 30's it came on! I told him that unless it was in the 20s out side my electric stips dont come on usually. I dont have insulation so its a bit higher for me cause it seems as fast as i can pump it in it goes through the walls on cold days. The wood stove insert i installed last year have helped me keep it comfortable now though. I have not even cut heat on yet this year due to the wood. I actually cut my AC on the other week as i had not switched it off or to heat yet! The neighbor lives in a drafty 100 yr old home, but supposedly has had foam pored into the walls. But still has old windows.

 

[GPintheMitten]

Hmmm... I kinda like that idea. I wonder where that circuit is.

I have some swanky thermostat now, but I'd be happy to replace it with one that will do better.

I will look into both of these.

Thanks,
David

The heat strip should have its own breaker in your service panel.

Trust me fuggettabout the setbacks on your heat pump with electric resistive heat back up. It might be fine with gas or propane but you don't want it for electric except for an emergency or the odd really cold snap. It's like heating with your oven.

 

[MossflowerWoods]

The heat strip should have its own breaker in your service panel.

GP,

I've got 2 slaved 60 amp breakers marked "Furnace" and 2 30's marked "Heat Pump".

I suspect the two 30's are for the AC side, and the 2 60's are the heat side.

I was trying to look at the control panel inside the closet where the indoor unit is located and I could not see any jumpers or such there either...

Hmmm...

Be well,
David

 

[GPintheMitten]

I would try switching the 60 amp breaker off and check that the heat pump works. A heat pump runs a compressor and a fan blower to move air , much like central (cold) air conditioning... Just in reverse. It is probably on the 30 amp circuit.

My guess is that the resistance heat coil is the 60 amp circuit.

 

[jinjimbob]

Here is my issue. I set the heat to 67 during the day and 62 at night. I need it to be cooler at night so I can sleep.

Every morning for a couple hours the "emergency heat" comes on to warm the house up that measley 5 degrees. We have only gotten down to just barely freezing for a couple hours at night.

Last hunting season, set at 65 degrees, it seemed to run ALL DAY.

Is this normal? Do I call the home warranty company to fix it? What do I tell them is wrong?

MUST I set the thermostat so there is only a 2-3 degree difference?

What is the outside temperature most of the time?

At those temps of 67 Deg F, it is more efficient to leave it on 67 Deg F 24 hours a day.

Sounds like your heat pump is operating perfectly ok.

You can select the mode to run in for most heat pumps, it looks like yours is running in comfort mode, that is why the back up aux heat strips kick in. It thinks you want to get to the new set point in the shortest amount of time.

Change it to efficiency mode, this will make it heat just the heat pump, even though it might take a few hours to get the to the new set point. This is how I operate mine. In this mode, the air coming out of the vents will feel cooler, but its still warm, after all it is heating your house.

If it is really cold outside, it might very well run a lot of the day, BUT a heat pump running is still cheaper than running propane alone and certainly cheaper than resistive heat alone.

Leave your thermostat alone, if its a modern one, it will learn the heat losses of your house. It will become more efficient as time goes by.

In efficiency mode, your thermostat will use the aux heat if it thinks that is more efficient to use that than the heat pump. It will use the aux heat to perform a defrost.
My Bryant system use both the aux heat AND the heat pump when its really cold outside. The Aux heat has three levels of heat, and the heat pump has low and high compressor speeds. Your might too, the thermostat should tell you whats going on.

Do NOT disconnect your aux heat. The system can NOT defrost if you turn the aux heat off.

Leave all your vents fully open. Let the system do its job as it was designed to do. Closing the vents will cause the system blower to work harder, costing more money.

I see a lot of bad information on here, don't follow it.