I recently installed a 750mv thermostat on our gas fireplace.

The on/off range of the thermostat seems to be too wide. It's either too hot by the time it shuts off and too cold by the time it turns on. The unit is mounted in the same room as the fireplace near the main furnace thermostat (not far from where we sit).

Does anyone know if it's possible to adjust the range on the thermostat? It's a new unit but not one of the digital/battery powered models. It's got what appears to be a mercury bulb inside.

Thanks!

There should be a little dial inside with a +/- on it. You will have to play with it, but that is what sets the sensitivity. Personally I would invest in a digital thermostat.

Check under the cover for a heat anticipator, you can adjust the the cycle longer and shorter. I have a feeling there may not be one as the anticipator is a resistor normally used on the 24v units, ill check my truck for one in the morning



Here is what your looking for


http://z.about.com/d/homerepair/1/0/6/5/-/-/heat_antic_2.jpg


Some of them use a magnet to snap the contact closed but since u said mercury im sure it doesnt have that? IF it does its sometimes adjustable

When adjusting the "span", be sure to hold the dial and carefully move the arm if you have a mechanism like that in the picture to ensure that you don't break it.

The numbers on the dial indicate how much of a degree you have to be from the setpoint before the thermostat activates the switch. If you don't have this dial, then there may be another mechanism to adjust the span. See the operating manual for the stat.

When adjusting a heating anticipator, you set the anticipator resistance to match the current rating of the primary control.(gas vavle) When we set them up for a furnace we take an amp draw and set the stat to that. So a .8amp reading woudl require a .8setting on that stat

Eitherway its a longer shorter cycle adjustment.

I'll have a look when I get home tonight.

The tiny 2 page manual makes no mention of any of this (only temp calibration).

Thanks for the image TKG26, I don't recall seeing such a dial inside but I'm hopeful that I'm wrong. :)

Most residential mechanical thermostats don't have the anticipator any more. Maybe you can still buy them but I haven't see one for a long time.

I managed to figure out that the thermostat (rebranded by a gas fireplace maker) is a White-Rodgers 1E30(W)/1F30(W) and it is Non-Anticipated.

I guess this means I'm out of luck - argh!

Is this something that would come by default on an equivalent digital thermostat?

I would like to keep the thermostat as simple as possible and it's not something I've noticed or used on any other home thermostat.

No, not all digital thermostats have adjustable span (anticipator). However, you should be able to pick up a manual thermostat with span adjustment for next to nothing these days. Lots of people simply throw them out when they replace them with digital/programmable ones.

I've got several in my basement from doing just that over the years.

Fireplaces are also somewhat tricky to control, especially if they are not the main source of heat, or off most of the time. I put in a simple light switch instead of a stat and turn it on if I'm cold and turn it off when I'm warm enough... The gas fireplace is in our basement and when I turn on the TV when I go downstairs in the cold weather I turn it on. Usually leave it on for a while then turn it off. The room is usually warm for the rest of the evening. If you wish more control than that, then obviously a thermostat is necessary, however, again, the thermostat itself has some mass and heat capacity, as does the wall it's on, so any stat may give you the issues you are currently encountering...

If you purchased an inexpensive programmable stat, you could have it prewarm the room, but it may still "overshoot" what you want during the first cycle. Once the room and walls are up to temperature, there is not as much over/under-shoot. I hope I've conveyed the issue enough.

You could also move the thermostat closer to the heat source.

I used to have a light switch and I replaced that with the thermostat. It has been installed directly across (facing) the fireplace and it is the depth of the room away - same as where we sit. The other side of the thermostat wall is in a powder room which itself is in the center of the floor (nowhere near an outside wall). Since the main household thermostat is just beside the newly installed one and the main heating system doesn't suffer from this "lag" I'm going to continue blaming the new thermostat for the time being. :)

Because of the house layout, we can heat our main living space with the fireplace without keeping the rest of the house too warm. I'm guessing (and I might well be wrong!!) that in the long run we will save money (although I'm not sure how much more efficient the furnace is versus the fireplace). What clinches it is the fact that we enjoy watching TV and seeing the fire going on the side.

If you check the outside (or inside) of the furnace access panel, you will find a label with "heat input" and "heat output", usually in BTU/hr. Divide one by the other and you'll have the efficiency.

for example 90,000 BTU/hour output, 100,000 BTU/hr input = 90% efficiency. The most efficient gas fireplaces are usually about 75%, with the fan running on full. Most are less efficient. There may be some information regarding efficiency in the fireplace operating manual.

By not heating the rest of the home, you may still be saving, as you say. We do the same as you... (heating and watching)

A furnace circulates air and a fireplace doesn't. A ceiling fan might move the air around and balance the temperature. You can try a regular fan, on low, to move the air and see if it helps.

some fireplaces(most) have a fans


In regards to stats, just be mindfull of what your using, This is a 750mv circuit an off the shelf thermostats are 24v and have higher resistance, while they may work if the heat anticipator is set to high the resistance through the antisipatore can eat up the millivoltage and leave nothing to energize the main valve. So the old stat once used for he furnace is not really a good application for a fire place. I have not seen to manymillivolt programables in the field locally. But one thing that is popular is a remote control you can get for the fireplace, It gives u on/off control as wel as timer and thermostatic control. It wall mounts or you leave it anywhere i the room your heating.(and is a millivolt system with 9volt power sourse so no power robbing circuits)

I did not have a millivolt stat instock today to check for heat anticipator but im pretty sure they dont use them... resistance being he issue