Separated combustion shop heater

[joe_padavano]

I'm pricing a heater for my new shop, looking at the hanging style propane heaters. Since I plan to use solvents and paint when the heat is on, I'm looking at separated combustion heaters where the combustion air is drawn from outside the building using a separate tube instead of from inside the building. Most vendors (Modine, etc) sell both conventional vent and separated combustion versions of their heaters, but the separated combustion versions carry a 60%-100% price premium. As an example, the one I'm considering is about $450 for conventional and $750 for separated.

I've downloaded the manuals for these units, and the only difference between the two is that where the conventional units simply have louvers in the sides where the heater draws combustion air in, on the separated units these louvers are blanked off and a 4" pipe connection is provided instead that is routed to outside the building. The only other thing is that the separated units have additional gasketing inside the case to ensure that no inlet air can be drawn from inside the building. Everything else in the unit - blower, burners, propane nozzles, etc, all have the same part numbers between the two units.

$300 extra to NOT punch louvers?! Seriously? Yeah, I suspect a large part of that price difference is for product liability insurance and lawyers, but you know what my next question will be. Why can't I seal up the inlet side of a conventional heater, blank the louvers, and add a pipe connection to outside? Assuming the airflow is the same (and the separated units all use standard 4" galvenized duct), the burner won't know the difference. This is even more attractive because used conventional vent heaters are readily available for even less money, but I have yet to find a used separated combustion unit.

Thoughts from HVAC guys?

 

[Steevo]

That pretty much sums up what I figured when I examined my Mr Heater unit.
It looks like it would be pretty easy to seal the intake side and build a fresh air intake.

Won't running the heater while spray painting result in buildup of caked on dry paint on the hot air tubes though?

 

[joe_padavano]

Won't running the heater while spray painting result in buildup of caked on dry paint on the hot air tubes though?

Good point, though I'll be using a spray booth fabricated from PVC tubing, plastic sheeting, furnace filters, and a very large barn fan, with exhaust routed out of the building. I'm really more worried about solvents, gasoline vapors, flammable dust, etc.

 

[Highbeam]

This is like the guy that buys a half ton truck and wants to add big springs to make it a one ton. The sticker on that heater will always say it is not a sealed combustion unit. You might think you made every conversion needed but did you really?

In this case, the only risk is that you will explode so only you need to be confident that you have it sealed up sufficiently.

 

[Angelfire]

You may want to look at the Sterling unit heaters (GG series). The units are separated combustion standard and are significantly less than the likes of Modine etc... They make up some of the difference with their exhaust kit but overall, still cheaper than buying a modine, etc... with separate combustion.
Cheers.

 

[joe_padavano]

This is like the guy that buys a half ton truck and wants to add big springs to make it a one ton.

No, it's not. In your analogy, the trucks have different frames, brakes, and axles in addition to the springs. In the case of the heaters, I did a part number by part number comparison, and the only difference between the two is the lack of louvers and the extra internal seals. The geometry of the air path, the blower motor, the burners, the nozzles are all identical between the two units. My proposed change is equivalent to removing an open element air cleaner and installing a sealed air cleaner with ducts running to a scoop under the bumper.

I posted this question on another forum and go into a similar discussion. Apparently it's OK for us (with no formal training) to completely reengineer an automobile that operates on public roads and potentially endangers innocent bystanders (installing front clips, mixing and matching brake system components, converting to rack and pinion steering) but anything non-automotive is impossible to do.

 

[joe_padavano]

You may want to look at the Sterling unit heaters (GG series). The units are separated combustion standard and are significantly less than the likes of Modine etc... They make up some of the difference with their exhaust kit but overall, still cheaper than buying a modine, etc... with separate combustion.
Cheers.

According to their installation manual, apparently all Sterling does to convert a conventional to separated combustion unit is to install a duct connector over the combustion air inlet on the unit and route it to outside the building, which gets me back to my original question...

 

[Highbeam]

No, it's not. In your analogy, the trucks have different frames, brakes, and axles in addition to the springs. My proposed change is equivalent to removing an open element air cleaner and installing a sealed air cleaner with ducts running to a scoop under the bumper.

Okay so lets change it slightly to, you are that guy that bought an F250 and should have bought an F350 for the additional payload capacity. The trucks are identical in year 2000 (I own an F350 of this year) except for a taller block in the suspension and a very important sticker that lists the allowable weights.

You THINK you know how to convert the heater, you THINK you have this figured out, maybe you're right but maybe you're wrong. The sticker on the heater doesn't care and can't be changed. The sticker, and serial #, will always list this thing as non-sealed combustion.

Your proposed changes to the heater are wise for several reasons. I like burning outside air. The manufacturer has no liability if the room explodes because of your non-sealed heater. That liability is probably what makes the proper heater cost more.

 

[joe_padavano]

That liability is probably what makes the proper heater cost more.

Which was what I said in my original post - the majority of the additional price was likely product liability insurance.

 

[StaggeringGoat]

The sticker on that heater will always say it is not a sealed combustion unit. You might think you made every conversion needed but did you really?

I'm gonna have to go with this. What if something happens? Is the insurance going to pay with a non approved/modified heater? What if somebody gets hurt? The judge isn't gonna want to hear "I fixed it myself". Even if something happens and it's not the heater's fault, it's going to look really, really bad.

It's been a while since I looked, but I noticed before that the sealed heaters were less efficient than the others, making me think there is more than just a difference of air intake...

 

[nehog]

No, it's not. In your analogy, the trucks have different frames, brakes, and axles in addition to the springs. In the case of the heaters, ...

If the only difference is the sealing, fine. I'm surprised they don't go with sealed relays on the external combustion air model--but they perhaps have sealed relays on both.

I'm gonna have to go with this. What if something happens? Is the insurance going to pay with a non approved/modified heater? What if somebody gets hurt?

I think you may have the best reason not to do it there... But like all of life, it is a risk issue.

... I noticed before that the sealed heaters were less efficient than the others, making me think there is more than just a difference of air intake...

I'm sure they are less efficient (the combustion air must be heated up no matter what.) But that loss of efficiency may be made up by the fact that you are not pulling cold are into the heated area. Down side is that your inside (heated) air is not 'replenished' or exchanged which can lead to a higher humidity level (perhaps not a bad thing) and/or smells not being evacuated from the area.

One must ask however, with the heater eight feet up, what are the risks of non-sealed combustion systems? (I'm asking, since I have wondered this myself...)

 

[joe_padavano]

If the only difference is the sealing, fine. I'm surprised they don't go with sealed relays on the external combustion air model--but they perhaps have sealed relays on both.

I did a detailed comparison of the parts lists (now the third time I've stated this in the thread) and ALL parts are the same by part number except for the side panels that are not punched with louvers (there's a duct fitting instead) and the use of additional seals on the combustion air inlet side.

Look, I realize you don't know who I am or what my technical capabilities are, and I appreciate the safety concerns. Be assured that no one cares more about my safety than I do. I'm also quite sure of my own abilities given 30 years as an aerospace engineer building and flying stuff in orbit (yes, with my own hands on the hardware), not to mention four decades of building various automotive projects and rebuilding our 300 year old log house (including all wiring, heating, and plumbing).

My hope was that someone with a real HVAC hardware background (not lawyer wannabes) would help me understand from a technical standpoint if I'm somehow missing something, or if the large difference in price simply is "because they can".

One must ask however, with the heater eight feet up, what are the risks of non-sealed combustion systems? (I'm asking, since I have wondered this myself...)

Back to my comment above - no one cares more about my safety than me. I know I'll be generating flammable vapors in the shop. While I doubt they will ever get to an explosive level, I'd rather not take that chance.

 

[brewchief]

Back to my comment above - no one cares more about my safety than me. I know I'll be generating flammable vapors in the shop. While I doubt they will ever get to an explosive level, I'd rather not take that chance.

A separated combustion heater will be safer in a environment with flammable but is not designed as explosion proof, if you want/need explosion proof you are looking for a whole different animal and I expect the price difference will be way more then the difference between the separated and non-separated units.

The reason the separated units are more expensive is fewer of them are made and they require additional testing to ensure they meet a UL listing, like anything else the more units you build the cheaper it gets.

Can you simply seal up a non-separated unit and add an intake and have a separated combustion unit? Sure can, will modifying the unit alter or void the UL listing? Quite possibly. If you have a fire that burns down your shop and your heater has been modified will your insurance company pay out or will they drag it out in court as long as they can claiming it was your fault even if it is not? That's the biggie and I can't help you there.

 

[Mike007]

I'm also quite sure of my own abilities given 30 years as an aerospace engineer building and flying stuff in orbit (yes, with my own hands on the hardware), not to mention four decades of building various automotive projects and rebuilding our 300 year old log house (including all wiring, heating, and plumbing).

.....And you can't afford the extra $300 for the sealed combustion unit?????

There are some things you could be missing. For one the burners on a sealed combustion appliance under certain circumstances can be operating under a different atmospheric pressure then the room the appliance is located in. For this reason the regulator on the gas valve is often vented into the sealed combustion area to equalize it.

I'm not trying to be a wise-*** and I know you don't want to hear it, but as soon as you alter it from it's original state, you void the UL Approval, AGA and any other certifications. Why even fool with it to save a lousy $300?

 

[paullie]

hell just crack the door a lil bit and turn on a fan, it will be otay

 

[Highbeam]

You sound like you already have an answer and came on here to try and get us to agree. When we didn't agree, you start calling names like "wannabes". The obvious giveaway was when you felt that you needed to impress us with your credentials to justify your answer to a question that you asked.

Your heater mod is a bad idea. Takes a UL listed non-sealed appliance and makes a non-UL listed liability if anything were to happen.

 

[funnyberger]

Joe,
I say go for it.
I'm not an HVAC guy and pretty young, so most of these guys will just scoff.
But $300 savings sounds great and I think you've thoroughly thought this all through. I don't care how much your make, I believe you should always try to be frugal.
By the way, I own a 1/4 ton pickup (03 Frontier). I'm hauling about a ton of auto body paint supplies in the bed for mobile recon. In seven years I've put over 100k on the odo. I had to purchase airbags for the rear suspension, and while they do go out after a few years, and cost around $350 to replace, it sure beats the **** out of owning/paying for a full size truck (for me). I love the tight steering radius and ability to maneuver through traffic like a go kart. Can't do that in an F-350!
Some times the world thinks there is only one way to do things, but it's just narrow mindedness.

 

[joe_padavano]

You sound like you already have an answer and came on here to try and get us to agree. When we didn't agree, you start calling names like "wannabes". The obvious giveaway was when you felt that you needed to impress us with your credentials to justify your answer to a question that you asked.

Your heater mod is a bad idea. Takes a UL listed non-sealed appliance and makes a non-UL listed liability if anything were to happen.

No, actually I don't have the answer. What I'm asking for is a TECHINCAL discussion, not a legal one. I fully understand the legal and insurance implications. As an engineer, I'm trying to determine if my analysis of the differences is correct or if someone with real hardware experience can tell me where I'm wrong TECHNICALLY, not legally or liability-wise.

I find it amusing that folks who are first to point out the legal and liability issues here are also the same ones who think nothing of mixing and matching brake parts on a street rod build or who put a wimpy Mustang II front end on a 3/4 ton pickup and then drive it on the street...

 

[Mike007]

I find it amusing that folks who are first to point out the legal and liability issues here are also the same ones who think nothing of mixing and matching brake parts on a street rod build or who put a wimpy Mustang II front end on a 3/4 ton pickup and then drive it on the street...

You are talking about 2 different things. My position comes from being in the HVAC business. If I alter a gas appliance and there is a loss of life or property, I'm on the hook for it. In fact insurance companies can deny a claim too for such things. I'm not saying it happens often, but I don't take chances.

It would be irresponsible of me to advise you to do something I myself would never do. And I already pointed out one technical issue you missed. What more do you need?

 

[madosta]

Sorry I can't help with the technical explanation. I love these debates - as a software engineer we see a lot of these questions - trying to explain little nuances and stuff.

Maybe take a look at a similar question here: http://www.garagejournal.com/forum/showthread.php?t=78566

There are some alternative heaters if you're looking for suggestions.

Maybe pickup the phone and call or email the manufacturer of the heater you are looking at. Someone there will have more advice/suggestion than many others. I'm interested to know the differences.

The most relative personal experience I have had is that I used to work with mobile computers, handheld barcode scanners. Intermec makes a 730 and a 730 Intrinsically Safe Computer

We shelled out $3000 more for a yellow shield and a different battery with a protective cap. I took them apart to verify those were the differences - yet we still had to pay for them for liability reasons. Talk about a scam.

At the end of the day, you probably wont blow yourself up, but what if your buddy uses your shop, etc. Good luck, let us know what you find out! Interesting thread.

 

[joe_padavano]

You are talking about 2 different things. My position comes from being in the HVAC business. If I alter a gas appliance and there is a loss of life or property, I'm on the hook for it. In fact insurance companies can deny a claim too for such things. I'm not saying it happens often, but I don't take chances.

It would be irresponsible of me to advise you to do something I myself would never do. And I already pointed out one technical issue you missed. What more do you need?

No, I didn't miss your technical issue. You missed the three times in this thread where I pointed out that ALL the parts of the two heaters I'm looking at (burners, ventilation blower, relays, propane nozzles, etc, etc) carry the exact same part number between the two units.

I would not expect an installer to alter a unit for a customer. Obviously your corporate liability insurance would not accept that, and since the customer is paying for the unit, not you, there's no financial incentive for you to do it anyway. I am asking about a device for personal use where any modifications would be made by me, for me, and I fully understand the risks - which I've assessed and based on the information I've been able to find appear to be pretty small. I'm having a hard time understanding what really is different if all the parts of the two units are identical per the manufacturer's manuals, but this is why I've been trying to have a meaningful technical discussion. Unfortunately, your prior post about possible regulator vending differences does not appear to apply to these two units according to the manufacturer's literature.

My analogy about modified cars is completely relevant. The overwhelming response to my question has been finger wagging about liability. In this case, I'm only creating risk to myself and my property, not to third parties (the building is on a 55 acre farm - there's no way a fire can spread to the neighbors). In the case of improperly engineered automotive modifications that are driven on public streets, innocent third parties are put at risk if one's underdesigned front clip installation or improperly matched braking system fails on the freeway and the vehicle crashes into a school bus or a carload of nuns. Yet, the topic of liability and insurance coverage rarely comes up when one asks a question about making such a mod on an automotive forum. Go figure.

 

[StaggeringGoat]

I find it amusing that folks who are first to point out the legal and liability issues here are also the same ones who think nothing of mixing and matching brake parts on a street rod build or who put a wimpy Mustang II front end on a 3/4 ton pickup and then drive it on the street...

Who said they do any of that ****? Yeah, you do something stupid on the street I'll yell at you for that too. The difference is car insurance doesn't fault you for DIY work. Cars are not UL approved.

Why don't you call up your insurance company and ask them what they think?

 

[Mike007]

No, I didn't miss your technical issue. You missed the three times in this thread where I pointed out that ALL the parts of the two heaters I'm looking at (burners, ventilation blower, relays, propane nozzles, etc, etc) carry the exact same part number between the two units.

I would not expect an installer to alter a unit for a customer. Obviously your corporate liability insurance would not accept that, and since the customer is paying for the unit, not you, there's no financial incentive for you to do it anyway. I am asking about a device for personal use where any modifications would be made by me, for me, and I fully understand the risks - which I've assessed and based on the information I've been able to find appear to be pretty small. I'm having a hard time understanding what really is different if all the parts of the two units are identical per the manufacturer's manuals, but this is why I've been trying to have a meaningful technical discussion. Unfortunately, your prior post about possible regulator vending differences does not appear to apply to these two units according to the manufacturer's literature.

My analogy about modified cars is completely relevant. The overwhelming response to my question has been finger wagging about liability. In this case, I'm only creating risk to myself and my property, not to third parties (the building is on a 55 acre farm - there's no way a fire can spread to the neighbors). In the case of improperly engineered automotive modifications that are driven on public streets, innocent third parties are put at risk if one's underdesigned front clip installation or improperly matched braking system fails on the freeway and the vehicle crashes into a school bus or a carload of nuns. Yet, the topic of liability and insurance coverage rarely comes up when one asks a question about making such a mod on an automotive forum. Go figure.

So....What was your question again?

 

[Highbeam]

Deleted my post, nothing to add.

 

[jjpp]

WOW! I can piss further than you. This stuff cracks me up.
In defense of the OP, he asked a fairly simple mechanical question that couldn't be answered here and wasn't looking for safety advise or reasons not to do it, as he clearly reiterated. He seems to have done some research on it before posting unlike most people yet people still want to beat him up.
I understand what you want to do but I would still not completely trust your modifications to be completely sealed. As long as you can except the liability aspect of it, and as long as you can maintain proper intake air volume, it appears all you are really doing is relocating the intake source.
If this was a used heater or something along those lines I'd be all for it but why not just buy the correct heater for what you are trying to accomplish?

 

[DPelletier]

1) congratulations on the decision to use a sealed combustion UH; it really is far better than the regular units for your described useage.

2) As a previous poster pointed out, sealed combustion doesn't mean explosion proof. I have installed many explosion proof fans and heaters and trust me; this isn't something you can/will afford for a residential application. Sealed combustion is fine.

3) I don't know the differences on the heater that you are looking at. Obviously I can't condone changing the heater's configuration. Most of the sealed combustion units I'm familiar with use a combustion air blower and most of the non-sealed combustion units don't. Simply adding a fresh air duct to the burner compartment wouldn't work on these units; without the combustion air blower, the restriction caused by the added duct would prevent the unit from firing properly.

Dave

 

[DPelletier]

For example, I've compared the Sterling QVF to the QVSF and the QVF doesn't have the combustion blower. From the factory literature on the sealed combusion QVSF: "A power venting system draws a controlled quantity of combution air from outside the building. Tyhe same system exhausts flue gas products to the outside. The burners, pilot and flue system are enclosed within the unit. The entire combustion process is literally unaffected by the atmosphere in the space where the unit is located".

The QVF has no such power venting/combustion system.

Dave