Replace 1960's vintage boiler?

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Old 12-10-09, 01:32 PM
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Replace 1960's vintage boiler?

I have a burnham holiday boiler no. 8-60 series 2 that recently combustion tested at 80% efficiency. I think the boiler was probably manufactured in 1960 based on the boiler no. It's 172k input and 140k btu output.

All the advice that I see is that if the boiler's over 15-20 years old it should be replaced. Why? If it's 80% efficient and has been reliable for 50 years, why drop a bunch of $ for something only marginally better? (I'm not interested in ModCon's because the extra cost of servicing and shorter lifespan make them uneconomical for my limited needs).

Presumably a new one would be smaller (my heatloss calculation is 90K btu Max) and have sealed combustion, electronic ignition, and perhaps less jacket loss (though hard to tell). Does anyone have any real world experience with the savings expected with a newer smaller boiler?

Right now we're using about 1150 CCF of gas per year or about $2300. I estimate that about 250 CCF of the 1150 are for DHW
 
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Old 12-10-09, 02:39 PM
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Originally Posted by dstrutto View Post
All the advice that I see is that if the boiler's over 15-20 years old it should be replaced.

Right now we're using about 1150 CCF of gas per year or about $2300. I estimate that about 250 CCF of the 1150 are for DHW
Not "all" the advice - at least not mine. But, I suspect you could call a few boiler salesmen, and many would advise you to buy a new boiler.

Let's assume that a new boiler would cut 10% from your total annual fuel bill - or $230 per year. If a new boiler, installed, costs $10,000, that would give you a payback period of 43 years. If a new boiler saved 20% in fuel, then the payback period would be 22 years. Etc.

Hypothetically, if you could buy a $10,000 boiler that somehow took zero fuel to run, the payback would be 4.3 years. That would be pretty attractive.

Buy a new boiler if yours is unreliable or has some serious problems.
 
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Old 12-10-09, 03:17 PM
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The combustion test is not the same as AFUE. There is much more to the puzzle than how well the fuel is burning. It still needs to transfer that heat into the water. So your boiler is more than likely less than 80% efficient.

You already know you will save more by having a smaller boiler. You can also save by intsalling an outdoor reset. That will adjust the water temperature based on the outdoor temperature. Combine the ODR, the smaller boiler, and a boiler that is 85% efficient, you will save some money. I can't say off hand. You may also be able to just install the ODR on your current model to save.
 
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Old 12-10-09, 03:53 PM
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I recently asked the same question you are asking yourself - Will I save money by replacing a currently reliable "vintage boiler" with a new, high-efficiency one? My current boiler is roughly 30 years old.

My local installer did some research on several boilers that qualify for the new tax credit and came back to me and advised me to stick with what I have until it dies. I started the conversation with him trying to give him $10k to install something new and he impressed the hell out of me by telling me to keep my money a few more years. He sat down and walked me through his cost-benefit calculations and they looked a lot like Mike Speed 30's.

One other issue that came up in that discussion is that the warranty terms are not as attractive on the new high-efficiency boilers as the manufacturers are not as confident in the new technology. He said that his factory reps were telling him that they are still selling more of the relatively less efficient cast iron heat exchanger models than the newer aluminum ones. Of course, that could just be a function of price (even after tax incentives) or it could be that installers are stuck in their ways and distrustful of new technology. Who knows... Even looking at the much less expensive "standard-efficiency" models the cost-benefit calculations led to the same conclusion... Use my current boiler until it is toast.

On the other hand, I did opt for the installation of an outdoor reset. I had my installer put in a Tekmar 256 controller on my existing system. I can't really say yet what savings I'll see as I had a minor issue with the configuration (in another thread, if you're curious). Others on this board seem to have very positive things to say about ODR. I'll post my experiences once I've got more data.
 
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Old 12-10-09, 04:09 PM
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Originally Posted by swkurth View Post
On the other hand, I did opt for the installation of an outdoor reset.
If you have over-sized radiation (which, like over-sized boilers, many of us do), ODR probably doesn't make sense. Just run the boiler at the lowest water temperature to avoid condensation in the flue (which will achieve maximum boiler efficiency). If the installed heat emitters keep the house warm, even during cold spells, you are at the optimum point - and no computerized ODR can improve on it.

Even if you replace your boiler with a smaller unit, it's the amount of radiation that determines whether ODR makes sense.
 
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Old 12-11-09, 05:18 PM
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Your advice is much appreciated. I come back to a question that I posed in another thread that wasn't completely answered:

http://forum.doityourself.com/boiler...cy-puzzle.html

If my boiler is 80% efficient at steady state, but only 50% (or slightly less based on recent calculations) of the heat is distributed by the air handler at steady state, what happens to the rest? Does 80% get burned, 50% get absorbed, 30% go up the flue as heat and 20% go up the flue as unburned gas? How do I compare apples and apples? What would the combustion efficency of 7 y.o. burnham series 2 84% AFUE be? If I buy a used 84% efficient boiler and hook it up, am I going to find that the air handler only outputs 54%?

There are some reasons that make me uncertain that the combustion efficiency test is completely accurate. Mostly, my 172K btu boiler only consumes 130k at full throttle. Does the reduced gas flow result in a reduced stack temperature and therefore an artificially high efficiency rating, or is the combustion test correct but allocated as in the prior paragraph? Do gas burners ever combustion test at less than 80% efficient?

As a final question, what is the minimum temperature to safely set a non-condensing boiler at? I was told 140F by someone, so that's where my aquastat is set.

Thanks much for your help with this!
 
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Old 12-11-09, 05:53 PM
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It's hard to follow all your numbers.

Can you give us the specific data that you are measuring or assuming - temperatures, flows, etc.?

For example, you say that only 50% of the energy winds up distributed by the air handler. 50% of what amount of energy? Measured how?

Energy can't be created or abolished. Probably there are some problems with your numbers?

When we say that a boiler's efficiency is 80%, that's output Btu/hr divided by input Btu/hr. Stack losses are part of the difference between 100% and 80% of input fuel heating value. A boiler's output Btu shows up in the heated water, pure and simple.
 
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Old 12-11-09, 06:00 PM
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As a final question, what is the minimum temperature to safely set a non-condensing boiler at? I was told 140F by someone, so that's where my aquastat is set.
Be careful with this!

Depending on how much cooler the return water comes back to the boiler, you could be in danger zone here.

You are firing with gas, correct?

The 'dew point' of gas fired systems is generally assumed to be around 135F. This means that if the flue gases contact any surface that is 135 or less, the water vapor in the flue gases will condense and take the acids with them, leaving a wet acid solution on the fireside surfaces in your system.

Let's say that your system has a 20 difference between supply and return water. This means that with your aquastat set at 140, your return water will be 120! FAR below the dew point. The system may condense MOST of the time, and this is bad.

You need to set your SUPPLY temp such that the RETURN water is 135 or above, for LONG ENOUGH TO DRY THE CONDENSATE THAT FORMS.

If you are firing with gas, I would never recommend you run the aquastat at less than 160F to be safe. And this is based on a 20 degree diff... even 160 isn't safe if your diff is 30 degrees...
 
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Old 12-11-09, 06:40 PM
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You can attach a magnetic thermometer on the outlet flue from the boiler. It needs to be upstream from any barometric vent, etc. Even so, the thermometer will read lower than the flue gas itself due to the temperature drop across the metal flue wall.

But it will give you a handle on the potential for condensation. My magnetic thermometer always indicates higher than 200 deg F.

A while back, we were out of town for about two weeks. While we were gone, the standing pilot on our hot-start boiler went out. When we returned, the circulator was running, the burner was not firing, and the boiler was down to cold iron. So, I lighted the pilot and the boiler lighted. Soon, major water (condensate) was running out of the boilerfront of my fire-tube boiler.

It's amazing the amount of condensate that can come out of a cold flue.
 
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Old 12-11-09, 07:37 PM
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My calculations are based on the heat output capacity of the air handler (First 36MBXB-HW) because all the heat produced by the boiler was distributed by the air handler without the boiler temp rising above 160F and without the aquastat shutting off the boiler.

The air handler specs are as follows:
At 160F input water temp with a water flow of 6GPM the air handler outputs 51.8k btu of heat. The input rate that I timed off the gas meter was 90K btu. 52k/90k = 57% efficiency, I rounded down to 50% because the taco 007 probably isn't supplying a full 6GPM.

If the boiler was combusting at 80% efficiency, the air handler should have received 90k x .80 = 72k btu of heat and returned the excess to the boiler causing its temp to rise. That didn't happen, so the output from the boiler must have equaled the amount distributed by the air handler. The aquastat was set to 180F and the boiler maxed out at 160F.

What happend to the extra 20k btu's of heat?

I'll up the aquastat to 160 just to be safe, but the boiler is demand fired and oversized, so, often in the shoulder season the heat call may be satisfied before the boiler reaches 160.
 
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Old 12-12-09, 07:19 AM
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With the method you used for the efficiency calc, there is also the pipe loss and the boiler jacket losses.

With an 80% combustion efficiency, 80% of the input BTUs goes to heating the water and heating the area around the boiler (jacket loss). The other 20% goes up the flue.

Al.
 
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Old 12-12-09, 08:13 AM
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Originally Posted by dstrutto1 View Post
The air handler specs are as follows:
At 160F input water temp with a water flow of 6GPM the air handler outputs 51.8k btu of heat. The input rate that I timed off the gas meter was 90K btu. 52k/90k = 57% efficiency, I rounded down to 50% because the taco 007 probably isn't supplying a full 6GPM.
You can't reliably go by the air handler's Btu/hr nameplate. You would need to precisely measure the water inlet and outlet temperatures to the air handler (probably to a tenth of a degree) and the water flow rate (probably to a tenth of a gpm). The nameplate data was probably derived in a laboratory with clean tubes (inside and out), clean fan blades, no-telling-what pressure loss in the connected ductwork, unknown (to us) inlet air temp to the air handler, and precisely measured temperatures and flow rates.

Using your approach, I could measure efficiency by adding up the manufacturer's specified Btu/hr ratings for all my old baseboard units, and dividing by the fuel input. Experience tells me that would be fruitless.

And, as OldBoiler points out, there is jacket and piping loss - most of that probably winds up in the heated envelope of the house.

If the combustion efficiency is 80%, then 80% of the fuel input winds up in your house (or attic) somewhere. That is the efficiency, not your calculated 57% or 50%.
 
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Old 12-12-09, 08:37 AM
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I measured the supply and return temps of the pipes at the boiler, and the temperature drop is about 20F with supply temperature of 139-145. This gives me a pretty good upper limit of how much heat is distributed by the air handler, and related piping losses to and from the air handler. At 4.5 GPM a twenty degree drop distributes 4.5gal/min x 60min/hr x 8.3btu/gal x 20F = 45k btu/hr. Input of 90k btu/hr

At any rate it's irrevant because that's all the heat into the house, the rest is jacket loss or up the flue loss. The jacket of the boiler is about 65-75F on the sides and 75-90F on top right near the flue. Ambient temp is in the low 50s in my basement It doesn't feel warm around the boiler like it would near a nice big 20k btu radiator, so I don't believe it's all jacket loss ... any ideas?
 
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Old 12-12-09, 09:10 AM
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okay, one more thing. I was just down there with my trusty infrared thermometer and testing the surrondings. Ambient basement air is 50F. Outside air is 29F.

The boiler sits on a 4" concrete stage and I tested the temp of the basement floor and stage. The floor 10' away from the boiler is 51F; at 3 ft away it's about 52.5F then within 6" it increases to 54F and then up to about 62F at the edge were the stage meets the boiler. Clearly some jacket loss is feeding mother earth.

It still doesn't seem like mother earth could eat 20k btu/hr. The floor would be 80F everywhere, right? (there's no-calculations to support that). Besides the boiler flames point up. Most heat must go in that direction.

For arguement's sake, is it safe to put some rigid insulation on the outside of the boiler and underneath it? I'll need to move or replace the boiler soon as part of a basement renovation, which is partly why I'm figuring out how inefficient it probably is.

Any ideas on how fragile a 50 y.o. CI boiler will be when it's disconnected and moved?

I'm all for keeping it until it dies if possible, since it's not otherwise causing problems, but I'd like to make it as efficient as possible. Is it possible to retrofit old boilers with induced stack vents and a fan in a can? I think the draft is pretty poor on the boiler. Smoke from a match gets diverted around the hood rather than up it.

If I keep it I will definitely do an ODR and post purge controls. What brands does anyone recommend? Any other tweaks to help the efficiency? Perhaps a flue damper if induced draft is not possible?

I'm very handy and can do just about all of that myself, but I'm willing to pay someone else if there's specialized equipment or knowledge required. I just want it safe, efficient and well done. Unfortunately I often find professional work somewhat sloppy. I guess DIY is taken for granted on this website.
 
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Old 12-12-09, 09:26 AM
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Originally Posted by dstrutto1 View Post
Any ideas on how fragile a 50 y.o. CI boiler will be when it's disconnected and moved?
Question: is the boiler insulated with asbestos? What is the condition of the lagging? What is the estimated weight of the boiler, and how do you plan to move it?

I wouldn't expect the boiler itself to be particularly fragile, but the insulation and refractory might be.
 
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Old 12-12-09, 09:45 AM
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ODR with hydro-air coil needs to be evaluated carefully. Performance really drops off with lower water temps, unless the coil is sized for the lower temps. Less risk in a partial reset situation, but still needs a hard look.
 
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Old 12-12-09, 10:09 AM
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Originally Posted by Mike Speed 30 View Post
Question: is the boiler insulated with asbestos? What is the condition of the lagging? What is the estimated weight of the boiler, and how do you plan to move it?

I wouldn't expect the boiler itself to be particularly fragile, but the insulation and refractory might be.

The boiler is insulated with fiberglass I believe. There might be some asbestos on the fireside of the boiler plates, but I'm not sure I would recognize it. I don't fear asbestos because I don't handle it everyday. I am more concerned about the excess "Mr. Clean" that I eat as a result of the residual spray on the tables at the local fast food joint.

What do you mean by Lagging and Refractory?

How heavy? Beastly heavy if not more. I moved a Rad that was 6'x2'x1' and it probably weighed 800lbs. I'm not sure why it doesn't fall through the floor. Wood is ridulously strong. The boiler is probaby in the same weight neighborhood. It's outside dimensions are about 3'x2'x2.5'

The only way I can think of moving it is with a couple of good hand carts. I have no idea of how I will get it onto the hand carts. I guess I'll just try to rock one side up to slide the hand carts under.
 
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Old 12-12-09, 10:40 AM
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Originally Posted by dstrutto1 View Post
What do you mean by Lagging and Refractory?
Refractory is the material on the inside of the firebox - to keep the flames from impinging directly on the boiler. It can crack and flake off.

Lagging is the sheet metal surrounding the outside of the boiler to protect the insulation and to hold it in place.
 
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Old 12-12-09, 10:41 AM
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Originally Posted by xiphias View Post
ODR with hydro-air coil needs to be evaluated carefully. Performance really drops off with lower water temps, unless the coil is sized for the lower temps. Less risk in a partial reset situation, but still needs a hard look.
I've been running the hydro air with 140F input for a couple years without heat issues. I'm more concerned about possible condensing with low return water, but I've seen no evidence of it.

What about old boiler retrofitting options?
 
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Old 12-12-09, 11:37 AM
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Originally Posted by Mike Speed 30 View Post
Refractory is the material on the inside of the firebox - to keep the flames from impinging directly on the boiler. It can crack and flake off.

Lagging is the sheet metal surrounding the outside of the boiler to protect the insulation and to hold it in place.
The lagging is okay. A bit rusted at the bottom in places. The piece that goes accross the underside of the unit looks pretty bad.

The refractory is gone as far as I can tell. it look just like rusty metal (but not crusty and decrepit) on the inside.
 
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Old 12-13-09, 05:25 PM
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Flue gas condensation in a cast iron boiler is way blown out of proportion. I am the first to be concerned about flue gas condensation. The truth of the matter is we use a temperature that has been around for 50 years. Back than the boilers fireside heating surface was less than in todays boilers. We get better heat transfer into the boiler water today. Residentially today it is hard to get a cast iron boiler to condense unless there is mucho water volume in the system. It can happen but not as it did in days gone by.
As Gil Carlson wrote, flue gas condensation and thermal shock are a result extremely cold water entering the boiler or cool water at a high flow rate. Other variables are laminar or turbulent boiler flows. The amount of fireside heating surface.
For every 100,000 btu's burned we get 1 gallon of water. This has become more of an issue in the chimney than the return boiler water temperature. Boiler protection today is the easiest thing to control. If we keep thinking in the 50's we will never maximize the potential of the equipment of today. Boiler delta T's do not have to run at 20f. It can run at 40f to stop flue gas condensation in the boiler. With working at high delta-T in the boiler allows us to gain system efficiency. I have a cast iron boiler working in an old gravity hot water system with large radiation and piping at a low return water temperature. The owner did not want a mod/con which would have operated more efficiently due to 3 rows of bricks and a plan for a future addition where the vent would be.
This unit has ODR and works on a minimum water temperature of 100f and a maximum of 140f. I used p/s piping and a Taco 00-VS with two sensors and a 40f delta - T dialed in. We are coming back about 8f cooler than supply at 100f. We add 40f in the boiler and go out above the condensation point.
No signs of condensate after the first full winter of operation last year.
 
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