# old thermostat = mercury poisoning??



## Ariell (Mar 28, 2005)

Well, I didn't really know who to ask about this but figured some of the knowledgeable people on ehmac would know a thing or 2 about thermostats....

Here's the situation. I live in a house that's been split into 2 apartments. The thermostat is in the upper (landlord's ) apt., the on/off switch for the furnace in mine.

How we've worked the heating issue in the past is that during the first part of the winter, we only turn the furnace on in the evening when we are both home. But then once it starts dropping below 0C continually, my landlord has asked me to leave the furnace on all day so that the pipes don't freeze. Well, I'm sure you can see the problem with this: we are heating an entire (empty!!) house for about 12 hours a day. That's ridiculous!  

Not being a homeowner, I didn't even know there was such a thing as a programmable thermostat, however, when I found out last winter, I thought it'd be the perfect solution and proposed it to my landlord. He said yeah, great idea but.... there's too many wires/I don't know how to do it/ what if it doesn't work and we have no heat?/etc. etc. So fine. I waited til the fall and again proposed the idea to him. Again he said he'd love to get one but now says that because it's an old thermostat that there is mercury inside and he is terrified of removing it.

Well even with my limited knowledge, I assume that you just need to detach the wires from the old thermostat and hook them up to the new one, right? I mean you don't need to physically dismantle the thermostat and even so, the mercury is enclosed so it poses no more danger than using a thermometer. Am I correct in thinking this? Is there really any danger in replacing an old thermostat or is my landlord just giving me the run-around?

Your thoughts please? Thanks.


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## Brainstrained (Jan 15, 2002)

When replacing a thermostat, one replaces the entire thermostat. There is no need to handle the mercury in an old thermostat (new ones don't use mercury), though the thermostat should be disposed of at a hazardous water disposal/recycling centre. There is no more threat to you from a mercury thermostat than there is from a mercury thermometer.

As for extra wires, I don't recall running into that problem the two times I've done it, but I do recall instructions in the new thermostat explaining which wires to use. It was pretty simple.

As for it not working, well, one can always re-attach the old thermostat, as the most complex and time consuming part of the job isn't attaching the wires, it's attaching the thermostat to the wall.

In general, unless a pipe is really exposed and has no surrounding insulation, it shouldn't freeze over 12 hours during the day in a Toronto winter. In most houses, the power switch for the furnace is away from the thermostat, usually in the basement near the furnace. Regardless of how cold or warm it is, most people probably turn the switch on in the fall and off in the spring and then use the thermostat control's temperature setting which really turns the furnace off and on. 

So he really doesn't need to worry about frozen pipes, but you don't really need to worry about turning the furnace on or off unless your paying for heat and/or he freezes/cooks you in your apartment.


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## Ariell (Mar 28, 2005)

Thanks Brainstrained. Yes, forgot to mention -- we do split the utilities bills. (Put that in the original message which seems to have gotten lost in cyberspace and I had to re-type it.) That's why I think it's crazy to be paying to heat the house when neither of us is home. And that's why I would like the programmable thermostat. He leaves the thermostat at a constant temperature now (doesn't want to be bothered adjusting it) so my shutting off the furnace with the switch is the only way to keep from needlessly heating the house all day.


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## BigDL (Apr 16, 2003)

Ariell said:



> Thanks Brainstrained. Yes, forgot to mention -- we do split the utilities bills. (Put that in the original message which seems to have gotten lost in cyberspace and I had to re-type it.) That's why I think it's crazy to be paying to heat the house when neither of us is home. And that's why I would like the programmable thermostat. He leaves the thermostat at a constant temperature now (doesn't want to be bothered adjusting it) so my shutting off the furnace with the switch is the only way to keep from needlessly heating the house all day.


You didn't mention what kind of furnace. You did mention pipes. I assume that the house is heated with a forced air furnace and not hot water. When you say the furnace is "turned on" do you know the temperature setting? 

The issue of pipes would be their freezing. Unless the building you are living in is prone to drafts from the outside especially directly on a water pipes freezing should not be a big problem. Except in extreme cold like - 15 C degrees or colder for a water pipe on an uninsulated outside wall.

Without knowledge of the construction of the house it is hard to say with any certainty what is good advice. 

Having a thermostat at 14 or 15 C degrees during the day when nobody is home would conserve a great deal of fuel. In most situations this would not pose a concern for freezing water pipes. 

I bought a house on the ground (no cement foundation) on posts. With electric baseboard heat, no insulation in the walls or roof the house cost a fortune to heat.

The water pipes under the house were the only ones that ever froze. It was an unheated area and would freeze at night (or coldest part of the day) especially during high windchill conditions when the heat was turned down in the house or when the water wasn't flowing.

The quick cheap solution (not environmentally of course) was to keep the water trickling. The next cheapest solution was to insulate the pipe and put "heater tape" a thermostatically electrical device under that insulation. The pipe did not freeze and the thermostat in the house could be kept at a lower level.

I eventually put a cement foundation under the house, a furnace and insulated from the roof to the basement. A very expensive solution but the pipes didn't freeze and I kept the thermostat at 15 C when no one was home thereby saving on heating costs.


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## SINC (Feb 16, 2001)

It's not always simple. when I put in a new furnace about 6 years ago, it came with four wires that could be run to the thermostat. My thermostat has only two. The installer rewired the furnace to work with the old thermostat. 

He wanted me to upgrade to a programmable at a cost of about $150 and I declined.

It's amazing how difficult it is to get along without one. In my case, I have to turn it down when I leave the house in the morning and back up when I return at night. 

Saved me $150 too.


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## Ariell (Mar 28, 2005)

BigDL said:


> You didn't mention what kind of furnace. You did mention pipes. I assume that the house is heated with a forced air furnace and not hot water. When you say the furnace is "turned on" do you know the temperature setting?


Yes, forced air. By pipes, I meant water pipes. Don't know the temperature setting since as I said I don't have access to the thermostat. I'm guessing it's around 20-22C which my landlord leaves as a constant temperature.

Sinc, thanks, but the issue is that I don't have access to the thermostat. And my landlord doesn't want to be bothered manually adjusting the thermostat, so he leaves it at a constant temperature, thus wasted energy and wasted $$. As for the difficulty installing a new thermostat, well, the guy has a phd in astrophysics. I'm sure he could figure out how to attach a couple wires.


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## Brainstrained (Jan 15, 2002)

Programmable thermostats start at $50. Most models are under $100, though the more programming options the more expensive. Regular thermostats range from $25 to $50.

The beauty of a programmable one is setting it to turn on 30 minutes before you get up in the morning (no more cold floor) or 30 minutes before you get home in the afternoon.


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## krs (Mar 18, 2005)

Canadian Tire often has programmable thermostats on sale at 1/2 price.
I just picked up a really nice Noma unit for less than $30 - big display, tons of features most of which I won't even use. Four program settings per day. Also includes a humistat to automatically control the humidity in the house if you have a furnace based humidifier.
As to wiring - it's dead simple. Just follow the instructions that come with the thermostat and make sure the wires don't drop into the wall cavety.


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## IronMac (Sep 22, 2003)

Just a quick note but renters are not supposed to be splitting the utility bills. It's actually illegal. Maybe Sonal or someone else can chime in on this?


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## RevMatt (Sep 10, 2005)

And I'm pretty sure that if you ARE paying the bill, even part of it, that means you get to control the heat. In any case, just wanted to chime in and say that we turn furnace right off every time we leave the house, and have never had a problem. After 10-12 hours it might be as cold as 13-14 when we get home, but our house is never more than 17 to start with, so unless your walls are insulated with newspaper, I think you should be fine.
Also, here in Ottawa, Ottawa Hydro has a program wherein they provide you with a free programmable thermostat. The catch being that during the summer, they can access it remotely and adjust the setting (within limits).


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## SINC (Feb 16, 2001)

RevMatt said:


> In any case, just wanted to chime in and say that we turn furnace right off every time we leave the house, and have never had a problem. After 10-12 hours it might be as cold as 13-14 when we get home, but our house is never more than 17 to start with, so unless your walls are insulated with newspaper, I think you should be fine.


I will do some research, but I recall reading that this practice uses more natural gas than allowing the furnace to remain on and maintain 14 degrees. While I can't be sure at this point, I will try and find out, but I suspect you may be costing yourself more in extra fuel by shutting it down than you save.


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## SINC (Feb 16, 2001)

Drat, I can't find it right now, but as I recall it had to do with the peak efficiency of your furnace. A cold furnace runs very inefficiently and therefore use much more natural gas than a warm furnace running at peak efficiency. 

Since it takes a furnace about 15 minutes or so to reach that peak, gas consumption is much higher for that 15 minutes of full blown "catch up" operation than it would use to maintain a lower setting like 13 or 14 degrees for the day as it would only run for a few 5 minute periods at peak efficiency.

It was something like that anyway. Something to ask an expert perhaps?


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## Beej (Sep 10, 2005)

I've read that that is a myth, Sinc, but can't say that I've seen the full "peak efficiency" argument before. Under normal settings, the furnace would frequently cycle on and off any way. The argument sounds like it is based on the heat-exchanger temperature.

The savings wouldn't be huge anyway, but I believe that the major factor is that heat moves to lack-of-heat (outdoors) faster with a larger temperature gap.


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## Macfury (Feb 3, 2006)

I think there's a strong "urban legend" component in the idea of NOT turning things off to save power--cars, TVs, furnaces. some sort of desire to prove that common sense is worthless in newfangled equipment. I suspect that this is probably true for nuclear power plants, however.


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## Ariell (Mar 28, 2005)

IronMac said:


> Just a quick note but renters are not supposed to be splitting the utility bills. It's actually illegal. Maybe Sonal or someone else can chime in on this?



 WHAT? Are you sure about that?? I see tons of places advertised where utilities are extra. Why on earth would it be illegal?


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## RevMatt (Sep 10, 2005)

Yeah, I've heard both arguments, although nothing resembling actual science on the subject. That said, this house came with high efficieny furnace that is only a couple of years old, and some of what I have read has suggested that the newer furnaces don't have quite as much variation between cold and hot usage. I dunno. We're just taking a stab at it with the best info we can find. In any case, it rarely sinks more than 2 or 3 degrees (given out low setting even with the furnace on), and I suspect that makes a difference, too.


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## CanadaRAM (Jul 24, 2005)

Ariell said:


> WHAT? Are you sure about that?? I see tons of places advertised where utilities are extra. Why on earth would it be illegal?


In general, these places would have separate meters. But for flippin' sure they would have separate thermostats.

Back to the original post: The mercury within a mercury bimetal switch is encapsulated within a sealed glass tube. In normal events, including replacement to the thermostat, one would never be exposed to it.

<Digression> 

I've always liked the lo-tech high tech of this: Two different metal alloys are fused together in a strip. The two alloys have different amounts of expansion at a given temperature, so as the temp rises, one side expands more than the other, and the strip bends, as a result. Take one of these strips and coil it up to muliply the effect (longer strip in a smaller space), anchor one end of the coil to a rotatable knob, then on the free end of the coil, put a mercury switch. 

The switch is a little tube with a couple of electrical contacts at one end and a ball of liquid mercury captured within it. Tilt it one way, and the ball rolls to the far end of the tube, but tilt it this side of horizontal, and the ball rolls to the contact end, and since mercury is a conductive metal, it bridges the contacts and turns on the switch. 

Then as the furnace warms things up, the coil expands, bends, and slowly tilts the mercury switch; when it becomes a certain temperature, the switch passes horizontal, the ball rolls to the other end, and the contacts are disconnected, furnace turns off. Until the strip cools off enough, contracts, and tilts the switch back on again.

I have to admit to admiring clever use of technology in the mechanical realm, more than advanced solid state electronics. I kinda know what they are doing in there, but it's not so easy to visualize and admire all those electrons rushing around inside of chips.

</Digression>


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## gordguide (Jan 13, 2001)

Check with your Power Utility; there might be rebates available. In Ontario there's $75 available for a programmable thermostat if you pay to have it installed. Somebody, probably the company that sells you gas, should take the old thermostat off your hands as well.


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## Ariell (Mar 28, 2005)

Thanks everyone for your input. I've called the gas co. and they will indeed come and take the old one off our hands.


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## Beej (Sep 10, 2005)

RevMatt said:


> Yeah, I've heard both arguments, although nothing resembling actual science on the subject.


Entropy?


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