Ask Your Question

Angie's List Answers is the trusted spot to ask home improvement and health questions and get answers from service companies, health providers and consumers. For ratings and reviews on companies in your area, search Angie's List.

Top 30 Days Experts
Rank Leader Points*
1 kstreett 240
2 Guest_9020487 110
3 Guest_9190926 105
4 GoldenKid 100
5 ahowell 95
6 KnowledgeBase 95
7 skbloom 80
8 Guest_98024861 70
9 Guest_9311297 70
10 Guest_9400529 70

*Updates every 4 hours

Browse Projects By Category

Question DetailsAsked on 1/31/2017

I had my gas fired boiler serviced for winter and the gas bill has increased dramatically. What would cause this?

Do you have the same question? Follow this Question

3 Answers

Voted Best Answer

First check your before and after bills for the billing rate - maybe your gas cost rates or gas cost adjustments on the billings went up dramatically and coincidentally around the same time - like ours went up 27% this month.

Other possible cause, especially if in a relatively mild winter area so standby heating gas (just to keep the boiler hot) is a substantial portion of your gas use - is perhaps it used to be set to fireonly when there was thermostat demand so the boiler went down to maybe 70-100 degrees if there was no demand, but now it is set to a constant-ready temperature option so it stays between maybe 160-180 and say 200-220 all the time (or higher temps if steam rather than hot water boiler). This can use a lot of gas, especially if the waste heat from the boiler staying hot does not help heat the house and thereby reduce the amount of firing needed.

Answered 3 years ago by LCD


I'll check my bills since that would account for some of it, I'm sure.

Also, some of it probably is the fact that even on mild days I left my thermostat at 73*, forgetting that it would still keep the water hot. I normally would have shut it off, so will have to remember to do that.

Thanks for your help! - I've been wracking my brain to figure out what changed. I'll also check with the technician to see if he changed any settings.

Answered 3 years ago by 1953Baby



This is Chris in Member Care. Thanks for your interest in Angie's List!

We'll be happy to help find top rated providers, but it doesn't look like you have a subscription to the List yet. You can join by visiting or by giving us a call. Our call center is available 8:00 am-9:00 pm weekdays and 8:00-5:00 pm ET on Saturdays.

Thanks for your question and we look forward to assisting you!

Answered 3 years ago by Member Services


You did not say what tempaerature you normally keep the thermostat at - but if set at say 73 degrees rather than 65, then if outside temp was say 45 that could account for theoretically about a one third increase in fuel usage (though of course at that relatively warm outdoor temp total fuel usage would not be large), at 30 degree outside temp that could account for roughly a 23% difference in fuel usage. At zero outside, roughly 13% difference by keeping the thermostat higher - though of course at those temps that would be a 13% increase over amuch larger total fuel consumption because it is overcoming a much larger temperature gradient from inside to outside.

You talk about turning it "off" - generally, it is not a good idea to turn boilers off, because they start rusting up inside and the water also stagnates and goes anaerobic in the circulating lines, promoting corrosion. Also, if you mean turning the power to the unit off, they do not like being turned off and on a lot - one of these days it might not turn back on. Also, if you are turning the power off (rather than just turning the burners off), the circulating pump is also turned off, promoting stagnation in the boiler and the circulating lines.

There is a lot of difference of opinion whether standing pilot boilers (ones where the pilot burns all the time) should be turned down to pilot only in the non-heating season (so the water stays at about 70-80 commonly) or off or left running. The arguments is totally off promotes rust, some say running the pilot does that because of the low exhaust temperature allowing the moisture in the combustion gas to condense in the boiler or in the exhaust flue. Personally, experimenting several years, mine rusted up a lot more turned totally off in the summer than when leaving the pilot on. And in our case, with cool or cold nights almost year around even in summer (Pacific Northwest) that 70-80 degree water in the system from only the pilot running is enough to keep the house at desired temperature as the thermostat kicks on as the day cools - just running that warm water continuously through the loops much of the day, but without "hot" water.

But certainly, turning the burners off saves a substantial (commonly $30-70/month) amount of fuel because the boiler keeps the water hot REGARDLESS of the thermostat setting on many boilers - though some only fire up if the thermostat is calling for heat. Obviously, the more thermostat demand on the boiler, the less "wasted" heat there is in keeping the boiler hot - to the point that during maximum heating days when the thermostat is calling for heat continuously there is no "waste" keeping the water hot because it is all being used. Conversly, in summer if the thermostat is not calloing for heat at all, then keeping the boiler heated up (firing maybe every 1/2 hour to hour or so commonly) is totally wasted energy if that heat is not wanted - or even more than wasted if it causes the A/C to kick in unecessarily.

Two schools of thought on the issue of keeping the boiler up to temp too - the constant-on option keeps the water in the boiler (assuming hot water hydronic heating system here, not steam) at about 160-180 typically - and refires to 200-220 max heat once it drops below that low range, regardless of demand on the system by the thermostat. So in warmer weather it might be sitting keeping that water hot without any demand for it. Certainly in truly (non-heating) weather that energy to keep the water hot is wasted, or even makes for more energy losses because the A/C then has to work harder in the cooling season, so if that is the case turning it off or down to pilot during the heating season makes perfect sense. In the sporadic heating season, whether turning it "OFF" saves energy depends on whether the waste heat radiating and rising off the boiler goes into useful house heating or not. If it is located in the "conditioned space" or in an area like a tuck-under garage, rather than in an unheated space or outdoor utility closet, that "waste heat" might not be wasted at all - it might be productively heating the house and just reducing the amount of time the circulating pump and heating loops are called on to heat the house.

For instance, in my house (tuck-under garage with water heater and boiler neat the center of the house) during cool but not real cold heating conditions, the waste heat from those two units keeps the garage at the desired temperature (about 60) without any operation of the heating coil unit in the garage - it only kicks on (using hot water from the boiler) when it gets into the 30-40 degree range, and only runs frequently once it gets below about 20 outside - so my effective heating season (about 10-11 months) efficiency, between using that wasste heat plus a vast majority of the flue gas heat radiating into the house from the flue chase up through the middle of the house, probably runs into the 98-99% efficiency range - despite the boiler only being rated maybe 70% efficient. So the decision on "shutting off" the boiler depends a lot on whether the "waste heat" goes into productively heating the house, and of course whether it is occurring during A/C season.

The other option (on units that have variable settings, or by adjusting the on/off setting or control relay at the boiler control unit itself), is to only allow the unit to fire when the thermostat calls for heat - meaning its response may be slow because it may be starting off with 70-80- degree water in the loops initially if in a season where heating demand is low (so thermostat only kicks on every hour or so, not every 10-15 minutes lioke in cold weather) - so it can take several minutes before the boiler gets up to temp and really starts putting out full heat at the loops. If you have plumber/HVAC guy out to look at the unit, or look in the instruction manual, it should indicste alternative boiler thermostat (not the one in the house on the wall) settings allowing you to control how much it cools down before firing again to heat the water, and also if it has the option of not firing unless the thermostat is calling for heat.

NOTE - on this latter option if boiler is in a place where it can freeze, one has to be careful because if the thermostat fails (so does not call for heat as the house cools off, say from dead battery), pipes around the boiler may get cold enough to freeze - especially if the unit does not have a standing pilot.

Answered 3 years ago by LCD

Related Questions

Terms Of Use
Privacy Policy