Turning off radiators to save money

[DAvid12846]

I have several cast-iron radiators turned off (and drained) to save on my heating bill. They've been like this for a few years, but a few months ago I turned off and drained another radiator. A few weeks ago the technician came to service our boiler for the winter. I live in upstate NY. I mentioned I might turn on the radiator that I recently turned off. He said I may as well turn it on because my boiler has such a large BTU that I'm not saving a lot of money by having the radiator turned off. My boiler is rated at 153,000 BTU's for heat and 133,000 BTU's for domestic hot water.

Is it true I might not be saving a lot of money by having the radiator off?

When the system was installed we had 12 cast-iron radiators (no baseboard). Five are now off and have been drained. I'm sure the total size of the radiators and length of piping has a lot to do with how much money is saved or spent on fuel oil.

Thanks - David

 

[Jadnashua]

Unless you live in a huge, leaky cabin, or you have a literally huge house, the boiler is WAY oversized! Unless you have a need for a very significant, frequent amount of hot water for domestic use, sizing a boiler to provide hot water above that needed to warm the house is an operational mistake.

Draining a section may do more harm than good, as the oxygen in the air allows things to rust...when filled with water, once the system is filled and run for a bit, all of the oxygen is used up and the water becomes inert unless you have a leak, and fresh water is constantly being added.

Are the areas with the radiators disabled actually still warm? How cold do you allow them to get? The only reason to drain the system IMHO, would be if there was a risk of things freezing, which generally, isn't a great idea in the house for various reasons.

IF the zone valve is never opened, leaving those radiators full should have no effect on efficiency, but not using them, could end up causing your boiler short cycling even more than it would normally by being oversized, than if they were in use. Short cycling the boiler shortens its life, and makes it less efficient in the process.

Without a good idea of the layout and radiation needs, it's hard to be specific on your installation.

 

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[DAvid12846]

jadnashua,

Except for the unused walk-out basement, the house is about 2,500 sq ft with very little insulation. Two story home. 3" of old 1950's rock wool in most of the attic (12" of fiberglass insulation over a 9'x12' room on the second floor), but no insulation in any side walls.

The unused radiators are stone cold. They were drained and valves on the individual supply and return lines to these radiators was turned off 4 or 5 years ago. The valves are just off the "zone" pipes in the basement and NOT at the radiators. Because of the layout of the house we have two zones (one thermostat) but one larger return pipe.

The boiler does not short cycle all that often, but I understand your point. I also see your point of oxygen and rust. On a typical day (25 degrees outside) I would guess the boiler might be on for 10 minutes then off for 2 hours. When it is 10 below zero outside, the boiler might be on for 15 minutes then off for 30 minutes.

I guess I'll turn on this one radiator that I recently drained and turned off.

I need to insulate this old 1860's house. The reason why the radiators were turned off (and all of those are on the second floor) was to keep the heat from melting the snow on the roof and causing water damage.

David

 

[Jadnashua]

It's usually not all that hard to insulate the upper story in the attic...but, you'd first need to do some air leak sealing. A building that old may very well have balloon framing, meaning a continuous channel from the lower levels up to the attic...you must stop that air flow, or no amount of insulation in the attic will solve an ice dam situation. For boiler cycle times you indicate, the boiler IS WAY oversized. Every time it starts up, it takes it awhile to reach maximum efficiency, then when it shuts off, a lot of that heat just goes up the chimney, wasted. Only when it is on for longer times does it start to become more efficient, and to keep from making a sauna, the thing needs to be sized properly.

For maximum comfort, it's better to have the boiler sized so that it needs to almost literally run constantly on the coldest design day. Running a few minutes per hour may be okay for keeping the house warm, but is horrible for efficiency and maximum comfort. It sounds like it would also be having fairly large swings in temperature. Once you seal the air leaks, it's pretty quick and easy in most places to add enough insulation to make a real difference. Doing it in the walls would help immensely, too, but I'd get the attic done first. Most places will loan you the blower, if you want to do blown-in insulation, and it may take longer to pick up and return the blower than it does to actually do the job! NYS has some fairly good rebates for energy efficiency upgrades (but those may or may not be going away with the new tax laws). Depending on income levels, you might get a lot of the sealing and insulating done for free. My mother lives in NYS, and I signed her up for their efficiency program...they did over $4K worth of work, and it didn't cost her anything. The house is more efficient and comfortable.