Vented vs. Nonvented heaters

My glass and wood greenhouse is 12 x 10. I can heat it for free with natural gas from a gas well on our property. So we're looking at heaters to buy. An unvented one will be much cheaper and easier to install. Do they really burn so efficiently that they're safe? Has anyone had any problems or success with one?

Go with vented. You will find that the oxygen will be depleted by the plant material in the middle of the night and you don't want that with a combustion heat source

But the the way I understood it, plants give off oxygen and use the CO2 given off by the unvented heater. I thought that the unvented was actually good for the plants, as long as they are efficient and only give off CO2, not any other waste products like carbon monoxide. Do I have that right?

Not at night. If you have a combustion heater, you need venting. Otherwise your heater will go out from low oxygen for the burner to work properly. No matter what, if there is combustion, there is oxygen used, so to be safe, I think vented is better.

Okay, I understand that.

Hi, Snoggle,

I built a small greenhouse about 6 or 7 years ago and installed an UNVENTED natural gas heater that I bought at Lowe's or Home Depot. I have had NO problems with any of my plants because of the heater. I grow orchids and keep my tropicals and cacti in the greenhouse each winter -- and everything blooms!

My greenhouse is a 10 x 12 lean-to built against a detached, unheated garage. It is wood frame with 2 glass storm windows and a door at each end -- one end has a regular size door and the other end has 2 doors kinda like french doors, but home made. The doors, walls & roof are covered with Suntuf panels from Home Depot with a layer of plastic on the inside ceiling and doors, and I sprayed white foam insulation to fill some holes. I installed some of the soft latex(?) door insulation around the doors. So the greenhouse is not completely air tight, but it's close. It's not very expensive to heat either, so there can't be much air loss. I live in zone 7 so we get pretty cold winters with lots of heat-stealing wind.

The first winter -- I monitored the temp in the areas of the greenhouse that are farthest from the heater and then added a small but heavy-duty greenhouse fan that has a water resistant motor. Now the temp in the farthest places stays the same as other areas - with the exception of directly over the heater which is, of course, hotter and used only for pots, sizzors, fan, etc.

The heater is wall mounted and the circulating fan can be mounted, but I just put it on a high shelf above the heater. I leave the fan on all summer too if any plants stay in and keep the doors at both ends open all the time. One summer a family of wrens nested right beside the fan (it was on) in a nest box I had put on the shelf to store for the winter. I was clueless until the hatchlings began to fledge in the greenhouse!

The heater I chose has a thermostat of sorts -- you can set the heater on about 8 or 9 different settings from high to low and it turns itself off and on accordingly. It doesn't have a thermostat that you set by temp, but I have a thermometer w/ the remote sensor in the greenhouse so I've learned from experience what setting to use for the heater depending on the weather.

I hope this is helpful. Perhaps I'm doing something wrong, but I've not had any problems with my gas heater. I seem to remember that it doesn't require a vent so perhaps the manufacturer has solved the vent problem?

Yeah, after DH and I discussed it further we decided to try the unvented one since the greenhouse has quite a bit of "venting" already (see my post "leaky greenhouse"). We'll just leave it a bit leaky (other than the one really big leak) and use a fan. Smackinsam - What brand is your heater? How many BTU's is it? I've ordered a remote thermometer. Where did you get the greenhouse fan? Do you remember the brand?
If it doesn't work out, we can just use the unvented heater in the (very, very leaky) tackroom of our barn, so it wouldn't go to waste. Worse case scenario, it goes out one night and I lose some seedlings. Most of what I will grow is pretty cold tolerant, not orchids or anything expensive and tender.
I just didn't know enough about them to know if they were safe, but according to DH if the heater goes out, the natural gas won't continue to flow into the greenhouse (I didn't have a clue about that). That's what worried me.

This link has a size calculator so you can get an idea of the size of heater or cooling fan.

http://www.littlegreenhouse.com/heat-calc.shtml

There is no such thing as an "unvented" heater. Every heater requires an oxygen source. If you're using an "unvented" heater, you need to leave the GH leaky. The heaters labeled as "unvented" won't work in a tight GH. Assuming it has a working oxygen depletion sensor (and it should) then if it works, your GH must be leaky enough. No manufacturer modifications will change that.

One common rule of thumb is one square inch of ventilation for every 1000 BTU of heat.

Stressbaby is correct. Even a vented heater will require a fresh air source. I was looking at a35K btu vented heater and I still would have to leave a 35 sq inch opening to have it properly operate. I opted for directvent instead. Exhaust and fresh air is all thorugh the same vent/intake pipe.

To Stressbaby --

I disagree with your claim that there is no such thing as an 'unvented' heater. I did a quick internet check and found numerous natural gas heaters similar to the one in my greenhouse and they are advertised as "vent free" or "unvented." I figure the manufacturers and sellers of these heaters know what they are talking about. These heaters have oxygen depletion sensors that will turn off the unit if there is insufficient oxygen. Also, if my pilot blows out accidentally, the heater also turns off the gas supply.

When I think of vented vs. unvented, I am thinking of the old heaters that produced dangerous gases as byproducts of burning the fuel. The byproducts are not good for plants or humans and those heaters had to have an outlet or vent to the outside where the byproducts were routed and safely disbursed. The new, more efficient-burning gas heaters do not produce the byproducts in sufficient quantities to be dangerous, which is why those heaters do not require venting to the outside --- hence -- unvented !

My heater is almost exactly like this one -- just a different brand.

http://www.heater-store.com/procom_mn200tba_vent_free_natural_gas_convection_heater_2754_prd1.htm

To Snoggle,

My heater is a Charmglo and it's almost exactly like the one at the following link. It's an infared heater with 3 ceramic tiles. In my message to Stressbaby I included a link but that link is to a blue flame heater. I then realized that my heater is not a blue flame heater, but is the infared. It has a pilot light and the 'flame' goes right up the ceramic tiles which glow orange. I believe I did some research at the time I bought it and concluded that the infared was more efficient for my needs and I've been very happy with it.

http://www.heater-store.com/three_plaque_vent_free_natural_gas_infrared_heater_procom_mn180tpa_2765_prd1.htm

Regarding the greenhouse fan, I purchased it from American Plant Products in Oklahoma City. I believe it is the 12 inch J &D GREEN BREEZE HAF FAN W/CORD
Order #: 55-VBG12 See the following link.

http://www.americanplant.com/greenhouse_cooling.pdf

American Plant Products is primarily wholesale, but will sell to individuals if you ask. My fan is NOT the typical flat & wide fan, but is shaped more deep - more like a small barrel made of coated wire. The photo below is similar to my fan.

Hope this helps! Let me know how your 'unvented' heater works out for you! I have one in my detached garage too.

Smackinsam,

You don't get it. Every heater has to have ventilation. Those labelled as "unvented" just don't include the ventilation as part of the heater. They rely on leaks.

Maybe I should more correctly say that there is no such thing as a working unvented heater.

To Stressbaby --

It appears you are confusing 'ventilation' with 'oxygen'.

What kind of 'leak' do you believe causes an unvented gas flame heater to be able to work? If a room is sealed tighter than Dick's hat band, and you operate a gas flame heater in that room without access to more oxygen than exists in the room, i.e., an outside source, then yes, the gas flame heater will eventually stop working when all the oxygen is used up. BUT, up until the oxygen is all gone, the heater will WORK just fine.

Also, please refrain from telling me what I get and don't get. We may disagree, but that doesn't make my opinion wrong!

Smackinsam,
Not confused.
Ventilation = oxygen.
Not literally, but functionally.
If your "unvented" heater works, then you obviously have enough leaks in your greenhouse to provide enough ventilation/oxygen for the combustion process.
You are also running the risk of buildup of various gases such as ethylene which is harmful to plants.
You are also potentially violating your building code.
But as my kids say, it's whatever.

Here is part of a description of non vented heaters:

"This heater is an open flame heater that does not need to be vented. Although it does require a fresh or combustible air intake from the outside of the greenhouse."

Non vented just means that there isn't a vent to remove the waste from combustion. Non vented heaters are supposed to burn so efficiently that there is very little waste other than CO2. There isn't any build up of harmful gases if things are working correctly.

Clearly there has to be fresh oxygen for combustion. Many people put in a hose or pipe to bring oxygen straight to the non vented heater if their greenhouse isn't "leaky" enough. My understanding is that, most non vented heaters have oxygen sensors that shut the heater off if the oxygen gets too low to prevent buildup of carbon monoxide.

Please keep things friendly.

Sarah

Suggested reading:
http://pubs.ext.vt.edu/2906/2906-1387/2906-1387.html
http://www.ces.ncsu.edu/depts/hort/floriculture/hils/HIL530.pdf
http://www.umass.edu/umext/floriculture/fact_sheets/greenhouse_management/jb_non_vented_heaters.htm

Hi everyone,

2 years ago, I bought a Mr. Heater Little Buddy propane heater. It has a pilot light (which burns continuous) and also a low oxygen sensor shutoff that is integral to the pilot light assembly. It worked fine until about 4 o'clock in the morning, when it would go out from the low oxygen (my guess). Since I did not have electricity in the GH, I put an open ended pipe near the heater to allow for constant fresh air. That worked great and did not create a draft.

Since then I got a bigger GH and now have electricity in there. I run an electric heater with a fan (about 3000 BTU) on high behind the propane heater (4000 BTU low or 9000 BTU high). The electric heater/fan keeps the air movement constant and there has been no pilot outage. The electric heat is not enough to heat the 8'X12' GH with low night temps here. I also have 2 circulating fans (electric) above the heaters. This is a huge improvement to evening heat the entire GH

Here's a pic of the small GH with the fresh air pipe

And here's a picture of my set up this year with the ceiling fans and the combo heaters

Stressbaby,

Thank you for the info on how the fumes can affect the plants. We had extremely cold temps last March, so I lined the GH with bubble wrap. This year has been a lot better and I had decided to remove the BW to allow for more fresh air from (leakage). Yes the tomatoes have started to droop during the night, so the BW needs come down.

Ahhh, Stressbaby ,

Have you realized yet that your last message proves MY point and proves that you were wrong?

You originally stated in Post #7569973 -- "There is no such thing as an "unvented" heater." Those are your exact words. I disagreed with that statement and you then rudely informed me that I “just don't get it".

NOW, however, everything you said in your last response is exactly what I've been saying--- that there IS such a thing as an unvented heater -- and --- an unvented heater WILL work. Yes, SOME unvented heaters will cause problems with plants and people due to unfriendly gases --- but I already mentioned that in my Post #7659408 -- BEFORE you told me that I "just don't get it."

In fact, the heaters that cause those problems are now prohibited by building codes for people-occupied structures. Contrary to your comment, I am NOT in violation of any building codes because my greenhouse is a lean-to built against a DETACHED garage--that means that the garage is not attached to the house. And, the type of heater I purchased is allowed in such structures by the local building code.

AND, I before I bought my heater, I did quite a bit of research about the vented vs. non-vented heaters (which you said do not exist) in order to decide whether I needed to buy a vented heater and build a vent into my greenhouse. I decided on the new infared gas heaters that don't have to be vented because they don't cause sufficient unsafe gases that will harm plants and people. Those heaters are very efficient.

And, as stated in my first response to Snoggle, I SUCCESSFULLY get orchids to bloom in my greenhouse, and orchid blooms are notoriously sensitive to ethlyene gas. I also grow tomatoes and tropicals and NONE of my plants have suffered from any ill effects from the heater --- despite the fact that the greenhouse is quite free of "leaks." I used spray foam insulation in nooks and crannies, and the doors have the latex tubing around them to close the gaps. The heater has a sensor that will turn it off if oxygen levels drop, but the heater has never shut itself off.

But that is irrelevant. I disagreed with your claim that there is no such thing as an unvented heater and you responded by attacking me personally. Now, your own 'evidence' proves you were wrong -- there IS such a thing as an unvented heater and it WILL work without a vent--it may cause problems, but it will work! Nevertheless, I somehow doubt you are the type of person to admit a mistake.

I agree that for safety's sake, people need to know that SOME heaters must be vented, but the warning can be given without a snotty, know-it-all attitude. And, while I do try to keep things friendly, I will not tolerate being rudely attacked for simply disagreeing with someone.

If I have offended anyone other than stressbaby, I apologize.

Wow I didn't think I had to spell it out. Last reply:

Unvented, literally, refers to a heater that "[has] no vent to the outside but dump all the products of combustion directly into the interior space." wfs: http://www.uky.edu/Ag/HLA/anderson/fl_prog/ghheat_u.htm

By using "unvented" in quotes, I was referring not literally to the existence or nonexistence of heaters labeled as unvented by the definition above. The quotation marks are meant to indicate that this is a misnomer.

I'm glad that you have had success with your heater. But although you took Vioxx and did not have a heart attack, we cannot assume that Vioxx is safe and does not cause heart attacks.

To be clear: all heaters require ventilation. Vented heaters have the ventilation mechanism built into the heater. Unvented, or vent-free heaters do not, and really on a ventilation mechanism separate and apart from the heater itself...a leaky GH or a separate ventilation opening or the like...for safe and effective functioning. The general rule is to provide 1 square inch of ventilation per 1000BTU/hr for these heaters wfs: http://www.umass.edu/umext/floriculture/fact_sheets/greenhouse_management/jb_non_vented_heaters.htm

No offense taken by me.

This message was edited Apr 3, 2010 7:42 AM

This message was edited Apr 3, 2010 7:47 AM

This message was edited Apr 3, 2010 7:55 AM

To Stressbaby,

So I was correct. You just can't admit you were wrong.

Now you are claiming that your quotes meant that you didn't "really" mean what you said----although you vehemently argued you were correct until you proved yourself wrong.

What about your statement that, "Maybe I should more correctly say that there is no such thing as a working unvented heater." Your sentence had no quotes so you have no excuse for the fact that your own information shows that an unvented heater WILL work. It may, or may not, cause unwanted fumes and gases, but it will work.

And, again, your snotty, know-it-all attitude rings loud and clear in your snide comment about Vioxx.

Are you still in grade school by any chance?

Alright you two........

Please stop it!!!!!!!!!!!!!!

It is making me feel all cold and prickly. I like to think that this is a warm and friendly place to be. Maybe you can Dmail each other and finish this discussion.


Just a thought

Amos