Short cycling

Drod

24 minute intervals and 6 minute cycles means you're off cycle for 18 minutes or 75% of the time, right? That sounds good to me.

Guy_2

Short cycling ?

Hello, is there a chart or rule of thumb as to what is considered short cycling of a boiler? As example, my burner that has a firing rate of 1.9 gph fires for 6 min at 24 min intervals. Thank you ,Guy.

Alan(CaliforniaRadiant)Forbes

Short cycling

(at least in my book) is firing for less that a minute. Six minute burn times aren't bad. It actually depends on what kind of day it is. The colder it gets, the longer the burn time.

If you're worried about the boiler being too large or a zone that's too small, there may be things that you can do about it.



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hr

Most importantly

the boiler has to run long enough to raise the boiler and flue above the condensing mode. I can't see many doing this in a minute or less. I think 10 minute burner on time is what a PM Engineer study found to be acceptable. Gas valves, relays, inducer motors, etc all live shorter than normal lives when the short cycle.

Of course a "perfectly" sized boiler would run non stop on a design temperature day. More and more heating pros are turning to buffer tanks as a way of running long hot burn cycles, especially on multi zoned applications in shoulder season applications.

Of course a modulating burner boiler would solve virtually all of the short cycle problems:)

hot rod

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frank_2

You didn't mention what type of system steam or hot water. If steam, your pressuretrol may be sensing a loss of pressure due to a faulty air valve or leaking packing glands at the rad. valves. After burner shuts down, and all rads are hot, get one your hands and knees and listen for slight hissing sounds from the valves. This has to be a very slight leak if it takes that much time for the burner to come back on, but it's worth the effort. I don't think it's the heat anticipator in the T"stat, but you can check that also. Match the adjustable scale on the T'stat to the VA rating of the primary control. Is the boiler producing DHW also? Then make sure your aquastat differential is properly set to about 15 degrees. Worth a try.

Boilerpro

Heat anticipator setting

> You didn't mention what type of system steam or

> hot water. If steam, your pressuretrol may be

> sensing a loss of pressure due to a faulty air

> valve or leaking packing glands at the rad.

> valves. After burner shuts down, and all rads

> are hot, get one your hands and knees and listen

> for slight hissing sounds from the valves. This

> has to be a very slight leak if it takes that

> much time for the burner to come back on, but

> it's worth the effort. I don't think it's the

> heat anticipator in the T"stat, but you can check

> that also. Match the adjustable scale on the

> T'stat to the VA rating of the primary control.

> Is the boiler producing DHW also? Then make sure

> your aquastat differential is properly set to

> about 15 degrees. Worth a try.

Boilerpro

Heat anticipator setting

According to experts here on the wall (if my memory is correct), for steam heat anticipator setting should be initally adjusted to 2 times the draw on the stat. Gravity hot water systems (or gravity conversions)also to twice the draw; convector hot water 1.5 times draw and forced air 1.0 times (unless its a "high -efficiency" 90% furnace). Steam and gravity systems have a much longer response time, so a longer anticipator setting is needed. If you have an adjustable cycles per hour setting on your thermostat, one cycle per hour is usually good for gravity hot water and steam, three for convector systems. This will improve economy and reduce wear on the equipment.

Boilerpro

Guy_2

Thanks to all , Guy.