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Old 03-22-2012, 02:31 PM   #1
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Wonder if Burner is Putting off adequate heat

Hello,

I recently got a new Frigidaire gas range. Mostly seems fine, but the second strongest burner (supposedly 13,500 btu) struggles to boil a moderate quantity of water (by moderate I mean about 7 cups in a thick aluminum sauce pan. It gets to a mild boil but will do no more unless the lid is on. I adjusted the flame with a tiny screw deep down in the middle of the burner control knob until it got as large as it could (as suggested by the manufacturer), but didn't seem to make much difference.

The flame seems to look OK, though it's proportionally a little wider than the largest burner flame (17,000 btu), which easily boils much larger quantities of water.

Does this seem normal? I had thought this amount of btu would be a cinch for boiling larger quantities of water. (It's under warranty, but if a service person comes out and finds nothing wrong with the range, then I might get charged, so I thought I'd get some input here first).

Thank you for your help

Steve

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Old 03-22-2012, 03:42 PM   #2
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How long are you waiting. I would expect it to take about 10 minutes to get a boil going with those parameters. Mathematically it should be near 5 minutes but with ambient loses and such I would double it.

If you call Frigidaire they may be able to give you a guideline that will be helpful. They aren't going to send someone out to look at it if they think it is operating fine, so they will want to discuss things and possibly have you do some testing first. Or they might just send someone, who can tell.

Is the flame clean? Any orange or yellow or is it a good blue?
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Old 03-22-2012, 03:56 PM   #3
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I didn't time how long it took to get to the weak boil, but I did let the pot boil for half an hour just to observe. Never got above that weak boil.

The flame's color appears as it should according to descriptions/photos I've read/seen (clear blue, an occasional wisp of orange now and then).

Frigidaire wasn't much help and gave me names of local authorized repair shops. I have to arrange for the visit but run the risk of having to pay out of pocket if they can't find anything wrong. Just seems that 13.5K BTU should be more than enough to boil 4-5 quarts of water, and I couldn't even get two quarts going strong. It even has "quick-boil" labeled on that burner's control.

Thanks for your response.

Steve
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Old 03-22-2012, 04:06 PM   #4
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You should be able to calculate how long it should take for water to boil on the smaller burner. Burner #1 is 17K BTU. burner #2 is 13,500 BTU (79% the power). So if a specific amount of water on burner #1 increases 100 in 5 minutes (for example), then the same amount of water should increase 100 in about 6 minutes and 20 seconds.
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Old 03-22-2012, 04:10 PM   #5
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13.5K BTU will boil 10 gallons of water. It is the amount of time that is the question, though at a certain point your ambient loses might overcome the ability to continue adding energy to the water...

If the stove isn't performing to your expectations and they wish you to pay for someone to tell you it will not perform to said expectations I would start considering a different stove and a return. When faced with that idea they might be more... understanding of your lack of enthusiasm.
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Old 03-22-2012, 04:16 PM   #6
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1 BTU is the amount of energy to raise 1 pound of water 1 degree Fahrenheit.

To boil water you need to get it to 212F (and then add enough extra energy for the state change, which really isn't all that important here). From 70F you need to raise it 142 degrees.

Generally the BTU rating of a burner is an hourly rating (13.5K BTU supplied in an hour).

From there it is math assuming no loses. 13.5K BTU is plenty to boil the amount of water you mentioned, an do it in a reasonable time frame.


One other thought... do you have other major gas appliances? Are you using the oven at the same time? Have you ever had gas supply problems in your house?
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Old 03-22-2012, 04:17 PM   #7
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If that's the case (that it should, under the right circumstances) boil so much water, then either it's not putting out the heat it's billed at or there's a lot of loss, as you suggest.

Unfortunately, it's well beyond the period that I can return the stove to the retail outlet where I bought it, and I declined the very costly extended warranty from the store. Very frustrating.

Thanks.
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Old 03-22-2012, 04:41 PM   #8
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Could the height of the grate above the burner contribute to this ambient loss? Seems to my untrained eye the grates are kind of high. This is my first gas stove, and since you can't really test them the store, I went on web critiques, which were generally very good.

Never had any issues with gas water heater & furnace.
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Old 03-22-2012, 07:23 PM   #9
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The boiling point is that point at which the liquid becomes a vapor, which is the temperature at which the vapor pressure equals environmental pressure. To make sense of this, you have to recognize that heat and temperature are different things. Adding heat does not increase the temperature in a boiling liquid. When you add heat to a boiling liquid, you convert more liquid (at the same temperature as before) to vapor.

So both burners boil water. Presumably, the higher output burner, being capable of adding more heat, will convert more liquid to vapor. Which you are certainly seeing. But both pots of water, both boiling, are at precisely the same temperature. More vigorous boiling is just vaporizing the water more quickly. And that it no aid to cooking by immersion. It might be an aid to steaming, because there's more hot steam in play.

If I put two identical pots, each with equal amounts of water, on two burners capable of releasing the energy in different quantities of gas, I expect the higher output burner to bring the water to the boiling point more quickly than the other. But once they're both boiling, if I drop an egg into each one, they will, but for minor unpredictable variations, cook at the same rate, because they are both immersed in the same temperature water.

The benefit of a higher output burner is that it heat more quickly, not ultimately hotter, because that upper limit is determined by boiling points, and we rarely work in the kitchen with boiling liquids other than water.

I have a range by a different maker but essentially the same ratings. I find that, for most purposes, the "power" burner rings the flame out too far for all but the largest vessels. Too wide for my tea pot and for my sauce pans. So I use the next smaller to boil most things, because otherwise the sides get the heat. It is not a fast boiler. Residential gas ranges are just not. They don't have the output.

Electric ranges typically have a main burner rated at 2500 watts. Now that's less than 9,000 BTU by plain calculation. But you can very accurately meter an electric burner. Gas burners are more complicated to estimate, and there are all sorts of variables, including high losses, perhaps as high as 50% loss from the ideal for the amount of gas consumed.

By rough calculation, if you put a big pot (to reduce other factors) with 8.5 quarts of 65F water on a burner and boil it at or near sea level in 16 minutes, you experienced the effect of an honest 12,000 BTU conversion, however it came about. If it takes 22 minutes, you got 9,000 BTU.

(My range is on propane, and although propane contains more energy per unit than natural gas, it burns cooler, so my range is rated lower on propane than on natural gas.)
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Old 03-22-2012, 07:34 PM   #10
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Are you boiling with lead on or off? Somehow from what you have posted it seemed to me, I might be wrong that you were boiling without the cover. If so, I don't think there is a problem. Open pot is not going to boil as hard as covered one. Of course that is obvious. But maybe you are expecting more from it, I mean the stove. How long have you had the stove? When did you notice this started to happen? If the stove is completely out of warranty, more than a year since you've bought it you can get one of the local outfits provide the service. For example here in MN the Excel Energy provides a service for all the appliances in the house. It is not cheap, but might be a good deal if something brakes. Since stove is not broken you can get such service and then set up a maintenance call. They should come out and take care of twitching without any problem.
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Old 03-22-2012, 08:41 PM   #11
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What he's saying reflects a lot of what I felt when I switched to gas. I suspect electric burners transfer heat to the bottom of a good pot more efficiently than gas burners do. That seems reasonable, because the whole electric burner is in direct contact with the pot, and gas has to heat essentially by radiation, and a fair amount of heat flows out to the sides. More heat is reflected downward.

My impression is that my old electric range boiled an equal amount of water more quickly. A Calrod's heating coil very efficiently heats the sleeve, and that's in direct contact with the cookware bottom. That's putting the water very close to the "fire," in terms of heat transfer.

I wouldn't go back to electric. The fine control and instant response with gas is very nice. Subjectively, it is also a more primal experience to cook over flame. But I recognize that if I want lots of gas heat, I need to go to a range that requires a 1-inch gas feed.
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Old 03-22-2012, 09:16 PM   #12
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First, thank you for the detailed and thoughtful response.

"The boiling point is that point at which the liquid becomes a vapor, which is the temperature at which the vapor pressure equals environmental pressure... So both burners boil water... And that it no aid to cooking by immersion...."

Point taken, boiling is boiling. But one thing with what I'm calling a "mild boil" is when I put in a pound of pasta, for instance, the water takes quite a while to bring back to a boil. With the high-power burner it reboils much more quickly. But it's the smaller, back burner that I want for pasta making so I can use the front one for whatever is to accompany it.

"Electric ranges typically have a main burner rated at 2500 watts. Now that's less than 9,000 BTU by plain calculation...."

My previous range was electric, and the 2500 watt burner boiled water, and reboiled after adding a large amount of pasta. So this is one reason why having a gas burner listed at 13,500 btu that seems so weak in comparison is frustrating.

"... if you put a big pot (to reduce other factors) with 8.5 quarts of 65F water on a burner and boil it at or near sea level in 16 minutes, you experienced the effect of an honest 12,000 BTU conversion, however it came about. If it takes 22 minutes, you got 9,000 BTU.

Wow, 16 minutes for more than 2 gallons. It took the 13.5K burner half an hour to boil a gallon. I can't imagine how long to boil 2.

I've started to wonder if it isn't the heat output that's the problem, but the stove design (just guessing, and this is the first gas range I've had, and it's certainly not a high end unit). The grates seem to be very high off the flame, with the exception of the largest burner. Maybe that's intended, but only the flame on the largest burner ever comes very close to the bottom of the pot. Seems like a lot of wasted heat. The side and back panel of the range and the far end of the burner grate get very hot. If the flame were closer to the grate (and therefore the pot), seems to me there would be less waste. Can't think of how to remedy that, though.


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Old 03-22-2012, 09:23 PM   #13
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I start covered, but leave uncovered for cooking pasta or potatoes. And maybe you're right that I'm expecting too much, but having never had a gas range, and having read up quite a bit, I am disappointed with this one aspect of the range. There is a 17.5K burner and it does the job like a champ. But I'm used to having a back burner for boiling water while I do other stuff on the more accessible and roomier front burner.

The stove is only a few months old and still warrantied, but of course I have to rely on an authorized repair shop, and if they don't find anything wrong with the range, then I'll be the one footing the bill.

Thank you

Steve


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Old 03-22-2012, 09:29 PM   #14
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Having looked at a lot of stove over the last couple years it seems that stove makers think I want to boil the water on the front corner.. I would prefer the jet drive in the back..
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Old 03-22-2012, 10:47 PM   #15
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Here here. You read my mind.
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Old 03-22-2012, 11:19 PM   #16
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Why don't they do it like my electric range - one big and one small burner in front, one big and one small burner in back?
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Old 03-23-2012, 11:34 AM   #17
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Quote:
Originally Posted by riversurf View Post
I've started to wonder if it isn't the heat output that's the problem, but the stove design (just guessing, and this is the first gas range I've had, and it's certainly not a high end unit). The grates seem to be very high off the flame, with the exception of the largest burner. Maybe that's intended, but only the flame on the largest burner ever comes very close to the bottom of the pot. Seems like a lot of wasted heat. The side and back panel of the range and the far end of the burner grate get very hot. If the flame were closer to the grate (and therefore the pot), seems to me there would be less waste. Can't think of how to remedy that, though.
It's really a matter of heat transfer, transferring heat to the bottom surface of the cooking vessel. The nature of a bag burner is that it is not very efficient at heat transfer. With electric, it's heat source in contact with pot. The nature of the heat source is very different with gas. Flame heat is complex, but at the tip of a methane flame, the temperature is about 320C, and temperature drops rapidly above that. Entire learned books are written on the transfer of heat by flame impinging on a solid surface. Obviously, there are many factors. Height above flame, reflectivity of the surface, heat containment, etc. And for our purposes, we want to know about efficiency of heat transfer from the bottom to the inside surface.

Electric is simpler. We worry pretty much only about the material of the surface and how well it involves itself in heat transfer, which is almost exclusively by conduction.

A gar range maker has a hard decision about grate height. Do we go low for more exposure to the hotter flame, or higher and have more diffuse heating without a hot ring. Electric doesn't call for that decision with the almost continuous burner surface. His decision gets easier when he realizes he just can't afford a real high capacity burner and has to trade off a bunch of holes up close for fewer holes set lower. There are technical and safety reasons for fewer, larger holes.

Compare this commercial gas range burner to your home range burner.



No more efficient, but LOTS more fire over more area. Maybe 28,000 to 35,000 BTU, requiring a large gas line. It's a brute force solution to the need for high heat.

It's practically easier to get big direct heat out of an electric device. A home range is fed by heavy wiring, equaled only by other electric heating device circuits. When home electricity was new, electric burners were pretty wimpy. They couldn't be more, because homes had electric supplies intended for very small loads, perhaps one light bulb in each room. Electric ranges have grown in power as residential supplies became heavier. But the 1/2-inch gas line was good enough for all gas equipment that was added. But it limited the size of range burners, which always had to consider that you might operate all burners and the over at the same time.

I accept the low heat output of home gas ranges. I really only notice it when heating a large mass, like a pot of water. But I'm at home and have the time. There's no rush, or shouldn't be. And I can always begin heating the water earlier and start with as hot as my water heater can make it (no kids, so it's cranked up). If I want quick recovery after dumping pasta into water, I will have to begin with a larger mass of water (most home cooks use too little) so the temperature won't drop much and wait for it to boil. Were I determined to boil water more quickly, even if it meant giving up the other gas advantages, I'd go electric. I read a lot before going to gas. I considered a commercial range, but decided the cost, amount of gas usage, and the construction necessary to meet code wasn't justified.
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Old 04-02-2012, 12:08 PM   #18
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All of this information (and I thank all the respondents) would all be more of a relief to me if I could get the water to a rolling boil on that back burner after I remove the lid. It just doesn't, no matter how long I leave the water on, It just simmers (not boils) away, with a few bubbles here and there, and a simmer is Not the same as a boil, especially if you want that water movement to toss the pasta (or whatever) around while cooking

The side of the the stove also gets so hot that it can't be touched, as does part of the back panel, making me wonder if this is just a poorly designed stove. The flames seem kind of far from the pot bottom except on the largest burner.

I'm sure this seems like a trivial problem to some who might be reading this, but to have a stove that doesn't boil water properly on a burner that, numerically, should do the trick easily, is a huge disappointment considering how much it cost.

As I mentioned, Frigidaire is useless in this so far. They require me to hire a "certified" repair shop, who is likely to charge me if they don't find a "manufacturer's defect"
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Old 04-02-2012, 02:01 PM   #19
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Quote:
Originally Posted by riversurf View Post
All of this information (and I thank all the respondents) would all be more of a relief to me if I could get the water to a rolling boil on that back burner after I remove the lid. It just doesn't, no matter how long I leave the water on, It just simmers (not boils) away, with a few bubbles here and there, and a simmer is Not the same as a boil, especially if you want that water movement to toss the pasta (or whatever) around while cooking

The side of the the stove also gets so hot that it can't be touched, as does part of the back panel, making me wonder if this is just a poorly designed stove. The flames seem kind of far from the pot bottom except on the largest burner.

I'm sure this seems like a trivial problem to some who might be reading this, but to have a stove that doesn't boil water properly on a burner that, numerically, should do the trick easily, is a huge disappointment considering how much it cost.

As I mentioned, Frigidaire is useless in this so far. They require me to hire a "certified" repair shop, who is likely to charge me if they don't find a "manufacturer's defect"
I don't think it's minor. If the burner can't boil water and the side of the stove gets that hot when a stove top burner is burning, there is a significant problem.

I think you should definitely call for service. I'd have safety concerns.
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Old 04-02-2012, 02:07 PM   #20
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Does the whole top of the range lift up on hinges attached at the back for cleaning. If so, has it been put back down as far as it is supposed to go?
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