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In article .com,
says...

Mark Lloyd wrote:
On Mon, 27 Feb 2006 15:11:12 -0500, Goedjn wrote:

On Mon, 27 Feb 2006 13:21:15 -0500, Keith Williams
wrote:

In article ,
says...
On Thu, 23 Feb 2006 00:10:28 -0500, someone wrote:

Are there any thermostats (any type) that are smart enough not to
turn on the heat at 10:55 when they are programmed to set back at
11:00? It seems wasteful and hard on the equipment to do so.

So make your setback 10:55. No wait then it might come on at 10:50.
So make your setback 10:50. No wait.....

So if it wants to come on at 10:50, let it but don't shut it down
until 11:00. If it wants heat at 10:55, don't bother.

Or if the thermostat demands heat at 10:59:59, turn the heat on,
but run it for X minutes even if the setback occurs.

If the point is to prevent short-cycles, either of the above would
do it. If the point is to save energy, set it back at noon. ;-)

Even if the furnace is running almost continuously, this in
only going to save you 1 extra start/stop cycle a day,
during the heating season. What's the point of even
worrying about it?

I know about the problem with short OFF periods (with a compressor).
What's the problem with short ON periods?

Well, too short of an off period for a compressor is obviously worse.
But, I think what he's worrying about is that short cycles for just
about any heating system are less efficient than longer ones. In his
case, the heat pumps will draw more current during start up and
probably doesn't reach peak efficiency for a couple of minutes.

Even a simple system like gas fired forced air has short cycle issues.
Every time it cycles, some energy is wasted at the end, where the
blower shuts down, but some heat still remains to be lost up the flue.
It doesn't likely really amounts to all that much if it happens on
average less than once a day, but it's still there.

There may be an issue on the other end too (perhaps more so). If
the thermostat is just about to be set higher and the heat is
already on, keep it in longer to avoid a short "off" cycle and
increase efficiency.

--
Keith