Actually, I think it's better to not artificially raise the daytime
temperature, but to allow it to happen by solar gain instead.

The reason being that plants tend to grow in response to warm temperature
and higher light intensity. If the two coincide, that is, when the solar
flux raises the temperature in the greenhouse, the plant grows normally.
If, on the other hand, the temperature is raised when there is no solar flux
to speak of - gray, cloudy days - one will tend to end up with leggy, "soft"
plants that might not be able to even stand up properly (in extreme cases).

My advice is to set your heating for maintaining a decent minimum
temperature, and let it go at that. It's better for the plants and less
expensive, too!

--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Books, Artwork, and Lots of Free Info!
..
"Steve" wrote in message
...
Keith,
I've been following this thread and I have an opinion, even though I don't
have a greenhouse.
Since you already have your heater system set up for day and night
temperatures, I think you should aim for a comfortable 10 degree (f)
difference between day and night. If you want to keep the night
temperatures no lower than 59f, then set the day temp for 69f. Now, I
don't think it would be necessary, or even desirable to keep the
temperature that warm all day (unless it is up there due to sunshine). I
would set that timer to be on from 11 AM to 3 PM.
I would either do away with the timer for the 59 degree setting or, if it
is easier, set it for the 20 hours of the day that remain.
Hopefully, you will have many days where greenhouse warms beyond 69
degrees before 11 AM and the higher temperature thermostat will not even
have to kick in.

Steve (wishing for zone 8 but more like 3)

kenty ;-) wrote:
I have a electric heater run through a thermostat controller & probe
which
is very accurate,I have two of this set-up one for day & one for
night,both
on timers so one set-up takes over from the other,it is automatically
done.I
just have to initially set the parameters I want,the night is set to
59f/15c
and day has been at 71f/22c,but today was really sunny in the after noon
so
the temp got in the 80`s.After input I have received off you guys I am
going
to lower the day temp to 66f/19c?What do you think.I live in Robin Hood
country,that being Nottingham,England,UK.It can get quite cold here(zone
8)but really not that bad!My greenhouse is only a measly 10x8,but we all
have to start somewhere.