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?