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twilightcall 02-09-2010 06:01 PM

How to stop auxillary heat from coming on defrost cycle and limit auxillary heat use?
Just for some background. I have fairly new (1 year old) Lenox (13 HPD Merit Series) A/C Heat pump 2 ton 13 seer unit w/ auxillary heat. I have a Honeywell Th8000 series thermostat. I live in Southern TN and it doesn't get too cold. I have an 800 sq. foot single story home with a 2 ton unit.

My problem is that my auxillary heat is coming too much and causing my bill to be too high. My thermostat won't allow me to lockout the aux heat less than 40F (that is if you have the outside temp sensor which I don't) and my Thermostat is very sensitive and won't allow for temperature differential settings. I can limit the aux. heat cycles to 2 CPH but that it is.

What is the lowest temp that I can safely run just my heat pump? I am pretty sure my heat pump can keep the house at 68 without the auxillary heat with temps in the mid 30s to 40s. What do you guys think? I don't want to overwork my heat pump but the aux. heat is costing too much.

My goal is to limit the use of the auxillary heat. Is there a way to stop the auxillary heat from coming on during the defrost cycle and I would rather have the heat pump run longer and not use the auxillary heat unless it is neccessary. I thought about setting the t-stat to 1H/1C heat pump (no aux heat) but the aux heat will still come on during the defrost cycle. What other options do you guys suggest? I only want to use the aux. heat when I really need it. Thanks.

jsmith929 02-09-2010 06:11 PM

Easiest thing would be to just buy the outdoor sensor and adjust from that,others can probably give you more advice on the programming.

twilightcall 02-09-2010 06:47 PM

The outdoor sensor will only allow me to set it to 40. I think I can get more out of my heat pump than that. IMHO heat strips shouldn't be needed until 25 or so right?

JohnH1 02-09-2010 06:52 PM

In defrost the aux will come on to keep from blowing cold air in the home. Defrost is basicly the same thing as running the a/c in the summer untill the coil is thawed. If the aux is comming on durring normal operation with the heat pump that normally means the heat pump can not keep up on its own and the aux is adding heat in addition to the pump. Is the aux running with the HP or by itself?

JohnH1 02-09-2010 06:55 PM

I missed the 40deg. Yes you can run much lower that that. with electric heat you should basicly run unrestricted. There is no reason to ever lock out the heat pump.

Marty S. 02-09-2010 07:12 PM

Disconnect W on the heat pump. You will not bring on the back up in defrost that way. Be forewarned the air coming out of the registers is going to be COLD in defrost with no tempering. Your 2 ton should be able to do all the heating for a 800 sqare foot house down to 10 degrees or so depending on insulation and windows.

twilightcall 02-09-2010 07:15 PM

Ideally I would rather the heat strips not come on until absolutely neccessary. They come on in the defrost cycle. I am not 100% sure but I believe with the pump on. If the temps don't get below 32 is there any reason I can't just run off of the heat pump? If so what would be the best way to bypass the aux. heat?

Also I am not changing the temp at all in the house. I just set it and leave it alone.

I know I can cut back on the CPH. Would it help if I set the t-stat to option 3 on 680 (room warmer than heat setting)

I am trying to avoid buying a new Tstat. The IAQ looks like the one with the good settings for aux. heat.

Awesome Marty. Thanks for the info. I was writing this when you posted that.

twilightcall 02-09-2010 07:17 PM

Marty disconnect W on the outside unit or at the tstat?

We have very good insulation and windows.

Marty S. 02-09-2010 08:45 PM

outside unit.

twilightcall 02-10-2010 05:59 AM

Is there a wire I can remove at the T-stat instead like the Aux wire or ?. Thanks.

Marty S. 02-10-2010 06:20 AM

No you don't want to remove it from the thermostat. An outdoor thermostat is a cheap option to consider. Can hook it up to break aux from the indoor stat so it can't run below x degrees.

twilightcall 02-10-2010 06:28 AM

Ok thanks. Don't know alot about outside thermostats but will look into them.

On my outside unit W1 (1st stage aux heat) should be the white wire.

beenthere 02-10-2010 06:34 AM


Originally Posted by twilightcall (Post 397426)
Is there a wire I can remove at the T-stat instead like the Aux wire or ?. Thanks.

Thermostat doesn't control strips during defrost. So the wire from the heat pump needs to be disconnected if you don't want aux heat during defrost.

The Honeywell IAQ(YTH9421) is the stat you should have gotten.
It would allow you to lock out the strip down to 5F if you wanted to.

Disconnecting the strips from the stat is a bad idea. If you were to go away and the heat pump fail. You could end up with frozen and broken pipes.

One way you can lock out the aux with that stat until you really need it is to install the outdoor sensor in your house.

You can install it in your return duct if you want, and set it to 60. Then your house temp would have to drop to 60 before the aux came on.

What CPH do you have your heat pump set to. The lower that number, the quicker the aux comes on. But don't set it higher then 4.

Another thing you can do. Is connect the aux heat to W3 instead of W2. That will delay aux heat longer.

twilightcall 02-10-2010 07:04 AM

Awesome info. I greatly appreciate it. I agree the IAQ is the T-stat I should have. I actually got the visionpro 8320 as a gift but at that time I didn't know how sensitive it is and that it wouldn't allow the lower setting of the aux. heat. I would really like the IAQ but I can't buy it right now.

I will have to check on my CPH. I honestly just started learning about this yesterday when I got my second extremely high bill. The CPH hasn't been changed since it was installed so I would guess it would be at what Honeywell has as factory for this t-stat. (8 or 9?) I also don't know what my compressor run time is set to. It is whatever Lenox factory is. (not sure if it is 30min, 60 or 90)

Can the outside sensor be wired in by the indoor air handler? The reason I am asking is my return air duct isn't very long. (maybe 2 feet long) My house is 800 sq feet.

I could set the aux heat to only 2 CPH but it would still come on when the defrost starts.
I do want to stop the heat strips during defrost. I think the defrost cycle is 14 mins max for my unit and I think I would be ok with cold air coming out for a little while while defrosting.

So while I am home could I set the t-stat to 1H/1C heat pump (no aux) to keep the aux from coming on until I can either wire the outside sensor to the return air or get an IAQ.

Thanks Again.

beenthere 02-10-2010 07:25 AM

As long as you reset it if your going away for any length of time(weekend, week etc). You can set it to 1 heat 1 cool. I'd also connect it to the W3 as I said before. So that when you go away, it isn't bringing in the aux heat right away anyways.

Yes, you can mount it near the air handler, or in the duct. The duct doesn't need to be long.

Your heat pump will remove roughly 5600 BTUs in 14 minutes of defrost. Most times it shouldn't be in defrost that long. But, the cooler the house is, the longer the defrost is. Disconnecting the W wire from the outdoor unit won't harm anything though.

The heat pump default setting is 3 CPH. Aux default is 9(which is a comfort setting, and too high for economy operation).

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