I have a simple question. The natural gas prices are skyrocketing in my area of the country. I have a large 100 year old home heated by two very old natural gas furnaces. I have always left the pilot lights lit during the warm months. Would the savings be worthwhile if I shut off the gas to the pilot lights during the spring thru fall season?
Thanks,
Stan
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Replies
I still have a 1945 coal conversion furnace. I don't know how much it saves in gas, but I turn my pilot off during the off season anyway. It's a pretty big flame. Also I have found that it adds a lot of moisture to the flue and it seems to rot out every few years, so maybe I can get another year out of it by turning the pilot off.
Well, you would save yourself some gas, for sure. However, you'd also have to relight the things every fall. You could have the service tech shut them down in spring (after the cleaning) and then you can relight them in the fall for the winter season. You could also retrofit an electronic lighter but that is unlikely to pay for itself.
However, your best bet is to satart saving money for the inevitable breakdown of your furnaces. A yearly inspection is pretty much mandatory to ensure that the heat exchanger inside them has not been breached and sending CO into the home.
I have been told that leaving the pilot lights can keep the heat exchanger just warm enough to prevent condensation and rust in the heat exchanger, and it is usually better to leave them lit.
If (i) you don't have central A/C and (ii) run a dehumifier in the basement, perhaps you could avoid that condensation.
Note: very much older furnaces tapped the pilot light before the main valve and a cooled thermocouple (if any) only prevents gas flow to the burners, not to the pilot, so don't just blow them out.
Also, do everything you can to avoid having the gas company get a look at those; in my area they red-tag them because of the lack of shut-off of the pilots from the thermocouple and you have to add an after market pilot light with thermocoupler shut off.
A very good explanation on the pilots. (keep them lit to avoid condensation problems within)
I most certainly agree.
Been there, done that.
I've heard it both ways -- that keeping the pilot light prevents condensation and saves the HE, and that burning pilot puts out moisture which can condense in the HE and cause it to rot. I tend to believe that second argument more.
>>I've heard it both ways -- that keeping the pilot light prevents condensation and saves the HE, and that burning pilot puts out moisture which can condense in the HE and cause it to rot. I tend to believe that second argument more.Well, there is moisture in combustion gases, but it is vapor until it condenses - I'd make an educated guess that the continual flow of warm air usually prevents that condensation - especially where the flue is shared with the water heater and there is a continual draft in the chimney.Furnaces with pilot lights are getting somewhat rare, but I've seen enough during the summer with the pilots burning and no greater amount of rust above the pilot light that I don't buy the second.I have only seen a few furnaces where the pilot was off for the summer so I don't have enough info to draw a conclusion for that state of affairs.
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Sojourners: Christians for Justice and Peace
The thing is, the pilot light creates more water vapor, and it's very acid vapor. If the fan is running then the HE will be fairly effectively held at room temperature -- the pilot light isn't nearly sufficient to keep it warm. If condensation could possibly occur, it will occur with the pilot lit.On the other hand, if the pilot isn't lit, the humidity in the HE is no greater than in the rest of the house, and the temperature of the HE will be about the same as the house (since the A coil is after the HE). (Lowest temp will probably occur just after the AC shuts off, if the fan shuts off too.) There's no reason why condensation should occur in the HE if it's not occurring on, say, the return air duct.
I accept the possibility that a lit pilot flame is a good idea for a boiler. However, on a furnace, I have a hard time believing that a warm HX will be any less prone to rust than a room-temperature one. Further, having had to destroy two chimneys in my house due to advanced decay brought on by a water heater in one case and a oil-fired furnace in the other, I have little good to say about adding a little bit of moisture continually into an unlined chimney cavity during the summertime. If your chimney is lined, this is another matter, but most chimney's are not...Therefore, a hygrometer (or whatever they are called) may discover that your summertime chimney is 90%+ saturated with water, just as ours was.
>>However, on a furnace, I have a hard time believing that a warm HX will be any less prone to rust than a room-temperature one.Try looking at a few thousand. And looking down a few thousand chimneys.FWIW, my opinions on this subject are based not just on theory or a couple of expeiences, but in having done several thousand home inspections. I don't say that makes me right all of the time, but put that forth "for what it's worth.">>Further, having had to destroy two chimneys in my house due to advanced decay brought on by a water heater in one case and a oil-fired furnace in the other, I have little good to say about adding a little bit of moisture continually into an unlined chimney cavity during the summertime. If your chimney is lined, this is another matter, but most chimney's are not...Could have been the appliances, but more likely it was badly designed chimneys.Tough to say without seeing them, but at leat in my area (NW Ohio) the biggest causes of excessive moisture in chimneys are (i) no rain caps and (ii) oiversized flues for the amount(s) of flue gases handled.In most cases where I have measured draft in the summer and where the chimney still handles both the furnace and water heater, there is a positive draft of up to 0.02 wcin, and sometimes more, before either appliance is lit-off. Where there isn't such a draft, the chimney is usually oversized for the appliances.It is my opinion that natural draft prevents the little bit of water vaopor in the pilot light flue gases from causing any significant amount of moisture.
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Sojourners: Christians for Justice and Peace
I'll defer to your experience any day of the week, thanks for sharing. Indeed, the two masonary chimneys were unlined and consisted of a single-tier of bricks creating 12x12 flue passages. Combine one of those with a single 50 gallon gas water heater and you have water-log city. In the basement, the brick had spalled itself into oblivion, such that there was a fist-sized hole in the flue. Even on the second floor the chimney was 90% water-logged.The other chimney was fed by two fireplaces and the oil furnace in the basement. Theoretically, it was in better shape (i.e. it had not imploded) but the mortar had crumbled out of it long ago, leaving lots of holes for combustion gases to seep into the house... Considering that the Williamson was a 200kBTU/hr-input monster, I suppose its flue requirements were actually quite close to the flue found in the chimney.So, I'll agree with you that if a flue is properly sized and drafts well (i.e. is lined to accomodate the appliance being attached) that a pilot flame will do little to nothing to a chimney. However, the lesson I took away from my rehab job is that having a dedicated flue for each combustion appliance is a big plus because it allows the flue to be perfectly sized for excellent draft, etc. This in turn led me down the path towards simplification, i.e. using a indirect water heater instead of something instantaneous, direct-vent, whatever. Thanks again.
>>The thing is, the pilot light creates more water vapor, and it's very acid vapor. Acid yes, but I'm not sure about "very acid."FWIW, this past winter my condensate line on my 90+ clogged and the genius who installed it made it inaccessible. So, while putting in my condensate pump, I drainsed the condensate into a bucket. On a whim, I tossed in soem baking soda, expecting to see it madly foam, like we did as kids making volcanos "erupt" with baking soad and (5% typically) vinegar.Barely a bubble, much less an eruption.>>If the fan is running then the HE will be fairly effectively held at room temperature -- the pilot light isn't nearly sufficient to keep it warm. If condensation could possibly occur, it will occur with the pilot lit.>>On the other hand, if the pilot isn't lit, the humidity in the HE is no greater than in the rest of the house, and the temperature of the HE will be about the same as the house (since the A coil is after the HE). (Lowest temp will probably occur just after the AC shuts off, if the fan shuts off too.) There's no reason why condensation should occur in the HE if it's not occurring on, say, the return air duct.Depends on where the furnace is located: if it is in a basement (as in many (some?) parts of the countryyou have to include the lower temps of the basement air in that calculation: you have ambient house air intermitently warming the outside of the heat exchanger, you have constant draft effect pulling basement air through the inside of the heat exchanger.(I don't see enouygh above-basement furnaces to have sufficient information to compare the two types of installation.)In my area, in most cases the basement is cooler (and more humid) than the house, even with central AC going.And remember that heat exchangers don't have much mass and change temp quickly.
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Sojourners: Christians for Justice and Peace
In our area there's no such thing as an unheated basement, at least not in homes newer than 40 years old. The furnace is always within the conditioned space.In any event, if the basement is cooler (and presumably wetter), the basement air will be cooler than the air in the HA (that is, the HA will be relatively warmer) and the basement air will not tend to condense in the HA before it condenses on other ("room" temperature) surfaces in the basement.
>>In our area there's no such thing as an unheated basement, at least not in homes newer than 40 years old. The furnace is always within the conditioned space.Yes, but we're talking about basements and furnaces and whether to turn off the pilot light in the summertime>>In any event, if the basement is cooler (and presumably wetter), the basement air will be cooler than the air in the HA (that is, the HA will be relatively warmer) and the basement air will not tend to condense in the HA before it condenses on other ("room" temperature) surfaces in the basement.Consider both during AC operation and between AC cycles (and no central A/C at all.)Actually, the air on the inside (combustion chamber side) of the heat exchanger may be be cooler and more moist at times during the cooling cycle than the air on the "outside" and that's when you could get condensation and rust - not from the moisture in the pilot light flue gases, but from the moisture in the basement air.(I don't know how to calculate the moisture in pilot light gases - but I can tell you that often a pilot light is putting out relatively high levels of CO as measured at (an inch or two above) the pilot light itself, but with no detectable CO at the top of the heat exchanger.)I would guess that any water vapor from a pilot light is similarly diluted to "undetectable" levels.That guess is more than a SWAG, and quite a bit less than a fully investigated scientific conclusion <G>
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Sojourners: Christians for Justice and Peace
> Actually, the air on the inside (combustion chamber side) of the heat
> exchanger may be be cooler and more moist at times during the cooling
> cycle than the air on the "outside" and that's when you could get
> condensation and rust - not from the moisture in the pilot light flue
> gases, but from the moisture in the basement air.Yep, and if the air on the combustion side is cooler, then, by definition, the HE itself is warmer than that air. So no condensation.
Consider both during AC operation and between AC cycles (and no central A/C at all.)
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Sojourners: Christians for Justice and Peace
The HE will probably be at it's coldest shortly after the AC fan shuts off (if it cycles with the compressor). When that happens, some of the cold air in the plenum will sink down and cool the HE. If the dew point of the air in the basement is higher than that in the conditioned space, then that's when condensation might occur (and is pretty much the only case when condensation can occur with the pilot out).However, if the dew point of the air in the basement is the same as the rest of the house (because the basement is a conditioned space), then necessarily the dewpoint is lower than the temp of the air in the plenum, the HE can't get any colder than the temp of the air in the plenum, and condensation cannot occur.If there is no AC, and just the fan is running, the HE will necessarily be warmer than the basement air (presuming a cool, damp basement) and no condensation can occur.If the fan is not running, the HE will be no cooler than any other surface in the basement (and warmer than cold water pipes, eg), so condensation won't occur unless the RH in the basement is near 100%.The important point to remember is that condensation only occurs when a surface is colder than the dewpoint of the air. Until the RH approaches 100%, condensation will not form on surfaces that are not being somehow cooled -- by contact with the earth (walls of the basement), due to cold water running (cold water pipes), or due to some sort of artificial cooling (AC).
>>However, if the dew point of the air in the basement is the same as the rest of the house (because the basement is a conditioned space)I guess you don't spend much time in basements.They rarely are the same temp as the rest of the house, especially older basements; the type that are likely to have older furnaces, such as those being discussed here.>>If there is no AC, and just the fan is running, the HE will necessarily be warmer than the basement air (presuming a cool, damp basement) and no condensation can occur.Why would someone run the fan in the summer if there's no A/C?
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Sojourners: Christians for Justice and Peace
I guess you've never spent any time in this part of the country. Our basement (30-year-old home) is living space (it's where our bedroom is), and is kept at the same temp as the rest of the house. This is common in this part of the country, since one gets a degree of earth sheltering, a help in both summer and winter. We have the original, roughly 70% efficient, standing-pilot furnace. (Actually two of them, one for upstairs and one for downstairs.)Also, our fan generally runs all summer, whether the AC is running or not. This is in part to take advantage of the cooler air in the basement, in part just to have airflow, and in part to keep the air fresher in odd corners of the house. (This is why thermostats have a "Fan" switch.)
I'd turn them off.
If your furnaces are old, you'd probably have a reasonable payback time by installing new furnaces. The old ones only had an efficiency in the 70's %, whereas the new ones are in the 90's. So, you'd cut your gas bill roughly 20%, which you could translate to dollars and evaluate your payback.
Before a new furnace, though, you should insulate whereever you can. Then you could get by with a smaller furnace, which would cycle less and be even more efficient, as well as have a lower initial cost.
Geeze....
Turn the puppy off...that way at least you'll be visually looking at the unit at least twice a year...
All the replies about condensation in the heat exchanger or not....Yikes
Thing wear out...that little pilot light will have such a small effect as to be negligible (it's kind of like calculus...no one was happy when it was "invented" because one of the intelectual tricks was to ignore the smallest part of the equations...& presto, we now have all kinds of high tech stuff that, without the math, wouldn't exist)
Save your money, look int energy rebates from your gas co. for 90% furnaces which vent through the sidewall
The water heater is harder...you have a harder set of options
There are forced draft heaters that can be side vented, there are on demand heaters that can side vented....both cost lot's more than a standard gas heater (although the change to "explosion proof pilots" in the code jacked up the price lately), and the installs are harder=more expensive...
I have a 90% side-wall vented furnace, but a standard gas heater...which I'd love to change to on demand so I can be "greener", but can't justify the cost/time to payback...