Is my system a millivolt system and can it receive Nest?

LenchoLibre

Can anyone tell me whether this Mars Furnace gravity furnace is a millivolt system, and whether compatible with Nest?

Not sure about the age of the furnace, we move in in the last year, and the house is almost 100 years old.  

Any insight will help, thanks!

Jamie Hall

I presume you have a conventional thermostat somewhere? If so, you can use a Nest, but whether that furnace is millivolt or not, you can't do it directly. What you will need to do is power the Nest with its own 24 VAC power supply, and use the Nest to control a relay. Take the two wires to your conventional thermostat and hook them to the relay's normally open contacts.

Be neat and label everything, please...

mattmia2

Is there a transformer on the ceiling somewhere or does that wire at the burner go directly to the thermostat? Some pictures of the terminals on the gas valve and of the pilot would tell us if it is millivolt. If it is millivolt, make sure the contacts on the relay are rated for millivolt.

JUGHNE

I believe the Nest tstat was designed with forced air furnaces in mind.....meaning quick heat up of air.

It looks like you have no blower/fan on the gravity air furnace.

So the Nest may have the same problems it gives some people who try to use them for steam heat.

Call Nest tech support and see if they know about gravity air furnaces.

wmgeorge

I would forget the Nest and put in a modern furnace.

mattmia2

wmgeorge said:

I would forget the Nest and put in a modern furnace.

It looks like they are in California so this might get used like one month a year.

wmgeorge

A Rats nest of wiring and a flexible gas line running right in front of the burner and soot marks showing its had flame roll outs for years. Yeah I would put a new Nest thermostat on this. Unsafe at any speed wither you live in California or not.

mattmia2

The flex line is part of seismic code. It could probably be in a better place.

tim smith

Yes millionth, no Nest.

Zman

I don't see a transformer in your pictures, so it is probably a millivolt system. You could add something like this https://www.supplyhouse.com/Taco-SR501-4-1-Zone-Switching-Relay?gclid=Cj0KCQiAjc2QBhDgARIsAMc3SqTB3Mkpi-qNEaGLGabyLWlgzVE0LCz6RKoG6vPcFvQctDQ6YdcOU8IaAsRrEALw_wcB but would need a 3rd wire at the t-stat to make the nest work reliably.

mattmia2

Zman said:

I don't see a transformer in your pictures, so it is probably a millivolt system. You could add something like this https://www.supplyhouse.com/Taco-SR501-4-1-Zone-Switching-Relay?gclid=Cj0KCQiAjc2QBhDgARIsAMc3SqTB3Mkpi-qNEaGLGabyLWlgzVE0LCz6RKoG6vPcFvQctDQ6YdcOU8IaAsRrEALw_wcB but would need a 3rd wire at the t-stat to make the nest work reliably.

I don't see a transformer but I have also seen it buried at some random location in the ceiling in old systems like that so it is likely a millivolt system but we need more information.

Motorapido

I operate a millivolt gas heater stove at my vacation property with a Honeywell wifi smart thermostat. At the recommendation of wise sages on this site, I bought a fan control relay to make it work. The fan control relay has a 24v transformer used to power the wifi thermostat. The thermostat then connects to the relay and the relay makes/breaks the millivolt gas valve circuit. I have a separate millivolt (hence unpowered) thermostat wired in parallel so that if the power goes out, rendering the wifi thermostat dead, the millivolt thermostat continuous to operate the heater stove.

LenchoLibre

Thanks to all who responded.  Yes, we are getting to know this old house that is new to us.  The “rats nest” of wiring is just the beginning down in that basement.  Was hoping to put a nest on here because we are familiar with the interface from our old house and basically I want to be able to program it to turn off during the day unless manually switched on.  Our gas/electric bill has been off the charts this first winter.  $400+ which is almost double what we are accustomed to paying in the winter.  

There’s an ancient battery powered Honeywell thermostat; sounds like I need to find the manual online and simply take the time to learn to program it.  Nest or similar smart thermostat probably isn’t in our future until we have the cash to upgrade the whole damn thing.  

I will definitely take a look at the safety concerns at the gas connection and maybe bring in a professional to clean it up.  

Jamie Hall

Chances are that that "ancient" battery powered Honeywell -- if it is programmable, and most of them were -- will do exactly what you need it to do with no fuss or feathers.

Your fuel bill will be affected by two things: how warm you keep the house and, more importantly, how good the insulation and draught sealing is.

Draught sealing is probably the easiest place to start, but by rather cautious about windows. If you have good storm windows and good old double hung windows, just making sure the double hungs work and fit well is what is needed. On the other hand, if someone replaced them with mid or low range "modern" windows, they may need replacement. What do you have?

Synbio

There's no screw on the C terminal, it's unlikely you could use a Nest without an external power supply. With that being said, it's straightforward to hookup a Nest with a relay and 24V transformer for someone who's a little handy. I think you have bigger efficiency issues here other than just the thermostat though.

ch4man

who on earth thinks is a good idea to put fuel injection on a model T? yes it is a millivolt system, zoom in on the gas valve and you see the thermopile connections. but back to the point, no a nest will only work with much modification and it still will be a gas hog. time to upgrade

Motorapido

ch4man said:

no a nest will only work with much modification and it still will be a gas hog. time to upgrade

Point of order. It's easy and very inexpensive to add a fan control relay so you can use a thermostat that requires a power source, and with that taken care of, the Nest will operate any millivolt system. I agree that the various whiz-bang promises of smart thermostats are largely smoke and mirrors, but the ability to monitor and adjust temperature while you are away from the property adds a great benefit. If you want to use a Nest, you can do so easily. Inexpensive, easy, and it certainly worked for me to connect a wifi Honeywell thermostat in parallel with my millivolt thermostat. I now have the best of both worlds. I do not lose heat when the electricity goes down since my millivolt thermostat continues to do its job. When the power is on, I can monitor temperature in my vacation house from anywhere in the world and adjust it if necessary. Here's how to do it. https://instructables.com/Nest-Thermostat-With-Gas-Fireplace-or-Other-Milliv/