cancel
Showing results for 
Search instead for 
Did you mean: 
Replies are disabled for this topic. Start a new one or visit our Help Center.

Nest thermostat : how to change to gas with dual fuel to speed up heating process.

Troddy
Community Member
3rd Gen Nest Thermostat and dual fuel time to temp threshold for changing over to alt heat
I have a 3rd Gen Nest Thermostat and a dual fuel system (heat pump + 2 stage gas) forced air system. The thermostat has been installed long enough that it can calculate time to temp. The heat pump and 2 gas heat stages all work perfectly when I use the test menu. I have the dual fuel outdoor temperature set to 40 degrees. When the outdoor temperature is below 40 the Nest correctly uses the alt (gas) heat.
 
My issue is that the Nest does not switch over to alt heat when the time to temp is high. For example it was 60 degrees in the house this morning and 42 degrees outside, when I set the thermostat to 68 degrees the estimated time to temp is 2+ hours and the Nest does not switch over to alt heat to heat our house faster. Does anyone know how to get the Nest to switch over to alt heat when the time to temp is high?
22 REPLIES 22

Revil
Community Member

I am having the same problem. My heat pump does not come on when outside temperature is reaches. I manually go to equipment and run test. Heat comes on and runs. This seems to temporarily fix problem. However, it does it again in a few days. 

Jake
Community Specialist
Community Specialist

Hey all,

 

Apologies for the late reply. I wanted to follow up and ensure you are good to go. Please let me know if you are still having any trouble from here, as I would be happy to take a closer look and assist you further. 

Best regards,
Jake

Jake
Community Specialist
Community Specialist

Hey all,

 

I want to ensure you are good to go, and everything is working properly. Please let me know if you are still having trouble, as I will be locking the thread in 24 hours due to inactivity. 

Best regards,
Jake

Eddie24361
Community Member

Yes I am having trouble. I am cold. After being away for a few days the temperature in the house drops to 50. The thermostat says 2+ hours to warm up the house. It would be more like 15 hours for the heat pump to bring the house up to 70. The gas furnace will do it in a couple of hours. How can I teach it if time to temp ≥ 30 minutes to use the gas furnace.

Rlr1999
Community Member

I didnt see a solution.  What was the solution to his problem?

MikeTN
Community Member

Accept how duel fuel works. HP over certain temp, Gas below. Or rewrite as two stage with HP as stage 1 and gas as stage 2

Eddie24361
Community Member

So what was the solution?

Troddy
Community Member

Thanks Jake. I’m looking for a way to temporarily turn on gas to heat up the house faster. 
if we are away and the temp drops, it takes many hours to get up to temp with the heat pump.

Tim

Eddie24361
Community Member

Just an update - I have been away for a few days and was coming home last night. At about 11:30 AM. I remotely changed the thermostat from 50 to 70F. When I went to bed last night at 10:30 PM. the temperature had made it to 69.  The heat pump had ran for 11 hours straight. The gas furnace can warm the house up in 2 hours but the Nest thermostat never turned it on. By my rough calculations it would have cost about $2 to heat with gas but cost $5 to use the heat pump. I am very disappointed that no one from Nest has given any solution other than everything is working properly. Apparently many people are having the same problem.

Eddie24361
Community Member

Final Update - returned to Home Depot. Six weeks and no solution. Look at the profile of anyone that replies to your question. Look to see if their other replies are all the same or have any validity. Apparently anyone can reply to a question and a lot of the answers are just plain wrong.

I know this isn't addressing your specific issue but you may want to configure the stat as a two stage thermostat. First being HP,second gas furnace. Set the differential for 2-3 degrees so 3 degrees below set point the furnace comes on. You can also stage by time. The outdoor sensor can still be used to lock out HP as needed.

You should also check the refrigerant charge. Sounds low. At 42 degrees out the heat pump should easily be able to heat to room temperature 

 

MikeTN
Community Member

the description your provided indicates the system is working properly from what I can tell. In a dual fuel system the switchover temp point you have set is 40 degrees. It doesn't matter what the time to temp is, If you are over 40 outside, it'll run the heat pump. If its under 40, it'll run the gas. thats it, super simple. 

when time to temp comes in is when its under 40 out, and you're running in gas mode, if time to temp is too long, it should kick the gas onto stage two. This needs to be wired and programmed correctly into the nest, and you also need the right dip switches on the furnace control. Sometimes furnace control is set to simply enable stage 2 after its been running on stage 1 for 15 or 20 min. Sometimes you have it controlled by the thermostat. 

 

I do agree with you that it would nice to have a option to run the gas heat when its over 40 out, but thats not generally how hybrid setups run. (over 40 = HP, under 40 = gas, very simple). And you would avoid this problem by not letting it get so cold in the house in the first place. 

And you would avoid this problem by not letting it get so cold in the house in the first place.

So just to be clear, I should have a smart thermostat but leave it at the same temperature all the time, even when I am going to be away for several days?

 

 

 

 

Do you go away several days multiple times per week? For daily schedules have the temp adjusted milder while you are out at work, but not so mild that it takes 4 hours for the heat pump to warm things back up. there's a balance between how  much energy you save during the day vs how much energy it take to restore a comfortable setting when you return. 

For those long weekends away, sure, set it further away from the normal temp. and since its a smart tstat, you can turn it back on the day you come home early, have the heat pump run during the day when its warmer out and most efficient, and warm the place up before you get home so you don't freeze for 4 hours while it warms it up slowly. 

The idea of dual fuel is to not use the gas unless the HP becomes inherently inefficient, not to avoid using the HP because it produces less BTUs and you want to warm up quickly. 

"I have been away for a few days and was coming home last night. At about 11:30 AM. I remotely changed the thermostat from 50 to 70F. When I went to bed last night at 10:30 PM. the temperature had made it to 69.  The heat pump had ran for 11 hours straight. The gas furnace can warm the house up in 2 hours but the Nest thermostat never turned it on"

also, heating from 50>69 taking 11 hours on HP or 2 hours on Gas does seem a little long. Wonder if your unit was undersized. When I go away for days at a time, I don't let it get down to 50, that barely keeping pipes in the wall/crawl from freezing. I stick to ############ usually for extended away periods. 

lastly as other have said, you could wire as dual stage instead of dual fuel. stage 1 being HP, and stage 2 being gas, but then you don't get the 40 degree switchover from HP>Gas. It'll run based on time to temp. 

the question I've had on these is that I've seen dual stage gas and dual stage HP, and I have no idea how you would wire/triggers so that both stages of both HP and Gas would get utilized. 

maryland
Community Member

“the question I've had on these is that I've seen dual stage gas and dual stage HP, and I have no idea how you would wire/triggers so that both stages of both HP and Gas would get utilized”

Our contractor said that we could not use our Nest (3rd gen) for a dual fuel, 2 stage Heat pump with Propane because we needed 4 wires (2 for propane and 2 for Heat Pump) and the Nest only has 2 for heat and one for cool so he said we would need to get the American Standard 850 Wi Fi thermostat. Nest should have updated their product to meet what HVAC equip is. Urgently on the market.

Typo:  meant to say HVAC equipment currently on the market.

That's the way we had it wired. The wiring wasn't the problem. Functionally it was correct. The problem was with the programing logic. There was no way to program it so that

if

"time to temperature" >  "acceptable recovery time"

and

"outside temp" > "compressor lockout temp"

then

use aux (gas)

else

use heatpump  

----

also never have it so the heatpump and the furnace run at the same time unless the heatpump is in defrost mode. If the heatpump is running and the gas furnace turns on it will overheat the heatpump coils and damage the heatpump due to overpressure.

 

I understand what you're looking for and agree that it make sense for certain people, but it's not a typical capability for a dual fuel system. I haven't found any thermostat that does what you want. I have the same requirement at my lake house and I accomplish it using the nest by simply changing the dual fuel switch-over temp temporarily when I want the gas heat to warm up the house quickly. I've never found anything on the market that offers a better solution. 

If it really bothered me, I'd simply install a relay to enable the gas furnace and control that with something like an Insteon low voltage switch module. 

I doubt this use case is common enough for any thermostat maker to offer as an off the shelf feature. I agree adding the feature is probably trivial cost since it just a programming logic change, but testing a certifying a feature like this costs a ton of money. 

Thanks for sharing!

efdoyle3
Community Member

Try looking at the Bosch BCC100 thermostat as a solution for dual stage gas furnace with heat pump.

Kittuv
Community Member

One option would be to user single fuel with aux heat. You can use compressor lockout for HP cutoff and aux heat kickoff temp to control furnace. Let's say HP cutoff at 20 and aux heat start at 40, it should run both HP and furnace between 20 and 40. Hope this helps.