The meltdowns was not why I was asking, but that would be the first thing I
checked. May meltdowns be something I never know about. I was wondering if
you set back the blower kick in (the middle set point) if you might not get
more uniform temps across the greenhouse. My little greenhouse works best
with the blower always on (controller set to manual). I have run it that
way a couple of years now. Watch the guys that set these, they are used to
setting them for humans in houses. There may be some oil savings in
dropping the low temp fan shutoff.

Pat

"Al" wrote in message
...
You mean in relation to the burner nozzle melt downs? Yes I know about it
and yes *I* have messed with it. :-) Last spring after the second melt
down I asked the maintenance guy to look at it and see if he though the
settings were causing the problem. He said it could very well be the
case, checked it out, adjusted them *both* a bit but said the settings he
had found on the one i messed with were probably not causing the nozzle to
melt. Maybe he was just being tactful. So far this year, knock on wood,
the gremlinated heater is functioning without problem. I use the
gremlinated heater as the main heater. I would not be able to sleep at
night if it were the backup knowing that it was the more likely one to
break down. Using it as the primary gives me a very secure safety net
should it fail with the same frequency it did last year.

"Pat Brennan" wrote in message
...
Al, Do you know about the fan limit controller and have YOU played with
it?

"Al" wrote in message
...
My heater eminence people were shocked at the size of the burner nozzles
that came with the heaters. They already reduced them and adjusted all
the other stuff to compensate. I only ran using the larger nozzles the
first year. One day I will learn to do this maintenance myself. One of
the heaters MELTS the burner nozzle about twice a year and nobody has
been able to figure out why yet. The other heater does not have the
same gremlin living in it and has never melted a nozzle or, for that
matter, had any real problems at all. Yet they are exactly the same
make and model and are configured the same way.

I appreciate the input. :-)

Actually what I want most is to find no bud blast at all every morning
when I check. It is down considerably this year (so far) as compared to
last year. When I grew indoors, at a much smaller scale, I don't
remember any bud blast and I attribute the difference to the environment
in the basement having more variables under my control, especially the
light. There was never a cloudy day in the basement. In the greenhouse
I am lucky if I get ten sunny days a month this time of year. I think
this plays a role in bud loss too.

I am probably going to run on double heaters a few more weeks and just
see how things work.

I still have plenty of coolish spots in the greenhouse. I have a few
cymbidiums and zygos in bud and ten I have an entire bench of masd in
bloom too.

"Pat Brennan" wrote in message
...
Hey Al,

I did not say which option would use less oil. It is a hard question
and I do not have enough information or remember the calculus. There
are two factors at play, the heat generation and the heat loss. On the
generation side it is more efficient to run one heater due to start up
efficiency and the loss of heat up the stacks. Heating the mass of
steel is no big deal since that is in the greenhouse and losses are
into the greenhouse. Barometric dampers will reduce the losses up the
stack, but they never work right for me and have lead to soot problems.
On the heat loss side it is better to have uniform heat for a given
average. As a greenhouse gets longer, at some length it would be better
to have heaters on both end than a single heater and a wide range of
temperatures. I have no idea what the length is, but one furnace is
not always the best answer.

If you opt for two heaters you might consider reducing the burner
nozzle size. Nozzles are measured in gals per hour and only cost a
couple of dollars. This will reduce the BTU output of the furnaces and
they will not cycle on and off as much. If you change the nozzle,
remember to reset the air intake. Also make sure your nozzles are
large enough for the coldest nights. (we use big nozzles that are not
always stocked on repair trucks--always keep an extra one on hand.)

I have seen the long plastic tubes used even when they are not
connected to the furnace directly. This would help level out the temps
(saving oil) but would add another fan to your electric bill. Watch
out for HAF fans blowing against the plastic as this leads to greater
temp and humidity loss as the warm air moves down the greenhouse I
have reduced the size of my HAF fans and been more careful adjusting
where they blow. I assume it has lead to oil savings, I know it has
help in growing.

If you think your greenhouses grow better with two heaters; increased
sales from better plants or faster growing plants will most likely more
than pay for the additional oil. Humidity will be more uniform in a
greenhouse that has uniform temps. How many blasted buds does it take
to cost more than the oil savings?

I like the temp difference across the greenhouse; oncs, zygos, and dens
go in the cold side, seedlings in the warm section, and mature phals in
the 'average' section.

Sorry I can not help, I have no idea what is best.

Pat

"Al" wrote in message
...
So you all are saying that I am burring more oil by what I am doing:
by running two identical heaters at 63.5 instead of one heater at 65
to maintain an average of 65 in the space I will spend more money?

"heating double the mass of steel and running each for half the time"
uses more oil?

The extra BTUs required to
"maintain the part of the greenhouse 2.5 degrees above normal would
not be
made up with the savings of only heating the other side to 2.5 degrees
below
normal" so I will use more oil?

Lacking some calculus equation I could not understand anyway, I'll
take your word for it. :-) I do kind of see what you are saying. So
the smartest thing I can do (since I was dumb enough to buy these
inefficient heaters anyway) is to set one heater at 65 and one at 63
so the second unit would only come on if the outside temps/winds
stressed the first unit's ability to maintain the temperature or
failed to start at all. My goal is to use the least amount of oil
while knocking the fewest buds off the phals.

I do like the nice even heat distribution I get with both heaters. I
kind of think some of the bud loss I got last year was from marauding
cold dry drafts in the circulating pattern. I will have to look into
a way to distribute the heat from one unit more evenly. Those clear
plastic tubes that hook in front of some heater brands and run down
the length of the greenhouse dispensing heated air though little holes
will not work because they can not be attached to the front of my
heaters. The manufactures told me so last year. If these things would
just hurry up and rust away, I would invest in a better method of
heating; probably a boiler with fin-tubes of circulating water running
under the benches.

"Ray" wrote in message
...
It is less-efficient to run two.

When a heater comes on, you pay to heat the heater in addition to
heating the air. If you plotted a curve of the percentage of energy
spent heating the hardware versus heating the air, it gets more
efficient with longer individual run times. The longer the burn time
per start, the more efficient it is. That's why it doesn't pay to
buy a 100K BTU heater when your need is for a 50K unit - it may heat
the air really fast, but it has to do so more often. The ideal would
be a heater that generated heat continuously at the exact rate the
greenhouse lost it.

With two heaters, you are heating double the mass of steel and
running each for half the time for each burn cycle.

--

Ray Barkalow - First Rays Orchids - www.firstrays.com
Plants, Supplies, Artwork, Books and Lots of Free Info!


"Al" wrote in message
...
ps. logically I come up with the same btu's must be needed to reach
the same average temperature, but is this the truth?

"Al" wrote in message
...
Hi,

I have a 30 by 100 foot greenhouse. I have two heaters, forced air
heaters, that burn oil. One heater alone is enough to heat the
greenhouse (on all but the coldest nights). They hang on opposite
side of the long greenhouse and the un-used one is a back up incase
the primary one dies. Two thermostats hang in the middle of the
space, 50 feet from the heaters about midway way from the floor to
the roof. One thermostat controls one heater each and they are
independent of each other. There are four temperature monitoring
stations in the greenhouse that are independent of the on/off
thermostats that are situated to read the two coldest spots and the
two warmest spots. The four spots are gathered from plant level
around the bench levels, (not extremely close to heaters or tucked
down in cold corners)

I can run the south wall heater with its thermostat set at 65 (in
the middle of the greenhouse) and the north end of the greenhouse
will register around 63 and the heated side will register around 68
but the air is circulated by LOTS of fans and the center air mass
where the thermostat is, is 65 degrees. The four temperature
sensors around the greenhouse average 65. The same pattern emerges
no matter which heater I use; the far side is cool and the heater
side is hotter but the middle is 65.

If I set *both* heaters to come on at about 64, both sides of the
greenhouse heat to around 68 and the middle of the air mass turns
on and off both heaters at 64. And they don't seem to cycle on and
off as often, and it seems there is probably more radiant heat
available from two heaters but that may be an illusion because the
outside night temperature varies a lot from night to night and this
has to effect how the heaters cycle on and off.

....anyway the average temperature based on the 4 monitoring
stations now comes to just under 66.... I have to set the
thermostats just about 63.5 to get an average air temperature of
65, so it matches the average air temperature of the single heater
number.

Here's my question, so by running two identical heaters at 63.5
instead of one heater at 65 am I using more oil, less oil, or the
same amount of oil to heat the same space to the same average
temperature? there has to be an equation that will answer this
question. Anybody know how to figure it?