Cutting fuel bill

zoom

I have a large (14,000 sq ft) circa 1915 property heated by a two-pipe vapor system running at about 6 ozs of pressure. The whole system works well, but I am trying to reduce the fuel bill.

Two questions:
1. Is it worth installing a chimney/stack vent? Currently, there is no vent installed.
2. The boiler is significantly oversized and will short cycle. Is it worth modulating the burner (I believe I have the right set up to enable that)?

I am looking for guidance on potential fuel savings.

pecmsg

A properly sized boiler will help.

Tightning the envelop has a larger return on invest

Jamie Hall

There is no vent? No vent at all? It doesn't have to be a stack vent -- many vapour systems didn't have them -- but it does surely need a vent. I would suggest -- if there is no other vent -- three Gorton #2s at the boiler where the dry returns meet up, before they drop.

While you're at it, make sure the crossover traps are working properly. Note that the system will heat without them working -- but it will be much more even and quick if they are working properly.

zoom

Sorry I mistyped.  There’s no damper (not vent) on the boiler exhaust that connects to the chimney stack.

Steamhead

zoom said:

Sorry I mistyped.  There’s no damper (not vent) on the boiler exhaust that connects to the chimney stack.

What type of boiler is it? Make and model?

Look at the original radiator valves and traps- what brand are they? Same for any devices in the piping near the boiler.

Where are you located?

zoom

The boiler is a WM 688. It is significantly oversized (I was naïve to what the plumber told me when I questioned that when the installation was done 4 years ago, I realize now that he was pretty unknowledgeable).

All of the fittings on the radiators are mostly original and in good shape. I replaced all of the traps (cross over and radiator) two year's ago. There is a single vent on the dry return that works well. All of the radiators get hot quickly.

The system operates at ~6-8 ozs and falls into a vacuum between runs. The boiler does short cycle on the radiator traps start to close down on heating.

I don't have any concerns on the system itself, just whether I can get the gas bill down in January with a damper installation or a gas modulating adaptation. Or perhaps that money is better spent elsewhere on greater insulation of the house envelope (I have some opportunities there).

Jamie Hall

Well, your best bet is going to be the insulation. That's the gift that just keeps on giving. Some would say that a powered damper on the breeching would help. Personally I've found them to be problematic -- if something goes wrong with it you have no neat -- but in principle they save a little.

Ideally one would have the burner modulate down as the pressure rose -- say full fire up to 2 or 3 ounces, then drop down. A two stage modulation would work well, though you'd need two vapourstats, of course, to control it. Would it save enough money on fuel to pay for itself? Um... very very hard to say. If the burner off cycle time when it is cycling on pressure is sufficiently short that the boiler never goes below a simmer -- say no more than a minute or two -- probably not.

What you may be able to do is to downfire that 688 somewhat, depending on where it is set now. It may not be all that much too big for your application -- I'd run the numbers on your EDR and it's square footage before I played with it much. Again ideally you'd want it to hold at perhaps 3 to 4 ounces until almost all the radiation was full, then rise to perhaps 6 to 7 ounces and shut off -- and cycle there until the thermostat was satisfied. And, again ideally, that 3 to 4 ounce plateau should last perhaps as long as 45 minutes.

The Steam Whisperer

Air tightening the envelop is usually the fastest ROI. This isn't just caulking window and doors and weatherstripping them, but getting into the attic of the top floor and sealing all the leakage points. This includes plumbing and wiring penetrations, the joints were interior walls meet the ceiling and especially, if you have plaster exterior walls that are furred out from the brick with 3/4 inch or 1 1/2 inch vertical furring, sealing the gap between the interior plaster and the brick. These spaces act like chimneys completely surround the living space. Once that is done, then insulate the attic.

We downfire those types of boilers all the time if they run on natural gas. Usually the gas burner has a broad input range, so it can be downfired significantly. We have a CI boiler rated for 2,800,000 input running with a mod burner running down to about 400,000 btu, with the high input at about 1,100,000.

dopey27177

If you are heating with oil install a smaller nozzle. 10% gph oil nozzle would help some, it is a cheap investment,
If you have uncovered steam piping in the basement insulate the piping that will help out a lot and work well with the smaller nozzle.

Jake

Jamie Hall

But note -- if you change the nozzle size, you must be sure that it is the right angle, and pattern to operate correctly in your fire box, and you will need to adjust the draught to suit.

This us NOT something which can be done by eye or "plug 'n' play". It requires the correct test instruments (and the knowledge to use them), and may require trying several different nozzle angles and patterns before you get one which works.

PMJ

@zoom,

An automatic vent damper was a very large improvement to my system. I have a 460BTU/HR boiler with a 10 inch flue and a tall chimney. There was no damper when I bought the place. It was like an exhaust fan. Today I won't consider running without one. It won't cut your fuel bill in half but I'd argue 10% anyway.

The straight up calculation of the heat lost cooling down the boiler is relatively small but also is only one part of the issue. Losing the heat from the boiler itself that doesn't have to be lost is one thing, but the air doing the cooling is air you already paid to heat so losing that for no reason doesn't make much sense. Most of us use this already conditioned air to feed the flame; but most of us have big boilers that don't need to run that much. So letting the boiler exhaust already conditioned air to what amounts to most of the time is just dumb.

Beyond this the lack of a damper will add minutes to time to steam on every burn. This will just cause greater temperature swings which only subtracts from comfort performance.

A vent damper will result in a much warmer basement which will then warm the 1st floor. You say your system goes into vacuum between burns - a damper will allow that vacuum to send more of the residual heat from the boiler to the radiators every cycle instead of up the chimney. So I ask why not take advantage of this?

As for longevity - just don't put it right on top of the boiler like the manufacturers do. They really don't like that. Moved away some they last a long time.

ChrisJ

PMJ said:

@zoom,

An automatic vent damper was a very large improvement to my system. I have a 460BTU/HR boiler with a 10 inch flue and a tall chimney. There was no damper when I bought the place. It was like an exhaust fan. Today I won't consider running without one. It won't cut your fuel bill in half but I'd argue 10% anyway.

The straight up calculation of the heat lost cooling down the boiler is relatively small but also is only one part of the issue. Losing the heat from the boiler itself that doesn't have to be lost is one thing, but the air doing the cooling is air you already paid to heat so losing that for no reason doesn't make much sense. Most of us use this already conditioned air to feed the flame; but most of us have big boilers that don't need to run that much. So letting the boiler exhaust already conditioned air to what amounts to most of the time is just dumb.

Beyond this the lack of a damper will add minutes to time to steam on every burn. This will just cause greater temperature swings which only subtracts from comfort performance.

A vent damper will result in a much warmer basement which will then warm the 1st floor. You say your system goes into vacuum between burns - a damper will allow that vacuum to send more of the residual heat from the boiler to the radiators every cycle instead of up the chimney. So I ask why not take advantage of this?

As for longevity - just don't put it right on top of the boiler like the manufacturers do. They really don't like that. Moved away some they last a long time.

I moved mine to the base of the chimney. Well, right where the pipe goes into it.

captainco

On boilers flue dampers can save about 3% to 5%. On oil they have to have a delay on them of several minutes after the burners shuts off or you will have all kinds of soot problems and smell problems.

zoom

Thanks everyone, great feedback.

I think my first order of business is attic insulation. Although the attic has a full layer of insulation, I do believe that the gap between the exterior brick wall and the plaster inner wall will act like a chimney. I do not believe that gap has been addressed. Aside from simply stuffing insulation in the gaps, is there a better approach?

I think the second item is the damper. Advice in placement is noted. Even 5% of my fuel bill will likely have a payback of maybe 4-5 years. I will make sure to keep spares on hand in case of maintenance issues.

Finally modulating the boiler, definitely a job for a pro (a good one off this site). Not sure on the fuel saving for that, so this one might be delayed to see how the other two work out.

Larry Weingarten

Hi @zoom , Air sealing is usually the most cost effective and first thing to do. Stuffing in insulation won't work as well as a more airtight approach, like spray foam in cracks, or caulking sheet metal in place around hot vents or chimneys. A quick search found this air sealing handbook: https://www.southface.org/wp-content/uploads/2020/05/Residential-Air-Sealing-Handbook.pdf It looks to have the basics. Sealing up the attic and then insulating like crazy is a good approach

Yours, Larry

The Steam Whisperer

I would spray foam the gaps at the tops of the outside walls. It probably would be best to use the soft foam made for windows and doors so you don't potentially blow out plaster. I would suspect if you really want to go first class, using fire blocking foam might be even better, especially around electrical boxes in the ceiling.

pecmsg

depending on depending on how tight you make the envelope consider reducing the size of the boiler.