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Boiler Installation


Zorfdt's Avatar
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09-03-17, 08:46 AM   #1 (permalink)  
Boiler Installation

I wanted to get the experts' opinion on how difficult is it to replace a gas boiler for a hot water (single-zone cast iron radiator) system? I have a 37 year old boiler which I think is due for an upgrade.

It seems like a pretty straight forward process... copper pipes for supply and return, gas/electrical, vents... Are there any gotchas that might make this more complicated than what I'm seeing?

I'm considering something like this - but still need to do some heatloss research and calculation to confirm the sizing.
GC124-25 - Buderus GC124-25 - GC124-25 75,000 BTU Residential Gas Boiler w/ Electronic Ignition (NG)

Thanks for any suggestions!

-Mike


Good luck... what's the worst that can happen?

 
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09-03-17, 11:08 AM   #2 (permalink)  
Yes if you have any form of cast iron heat emmitters then a boiler bypass is needed.. Often done with Primary/secondary piping...


Mike NJ




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09-03-17, 03:39 PM   #3 (permalink)  
Thanks Mike. I figured there was still more to know. All the gas boilers I've seen recently are 20+ years old, so I guess bypasses are a 'new' thing.

If I understand correctly, the boiler bypass will cool the water being sent out to the cast iron radiators from the 180 degrees that the boiler sends out, to about 140 so the radiators don't get too hot. It will reduce the boiler from short-cycling on and keep the room temperature more constant. Do I have that right?

The boiler bypass would look something like this:


Now I'm reading about Outdoor Reset. It sounds like for ~$200, you can get another 10-15% in efficiency on not-so-cold days. Why doesn't everyone do this?

Thanks!


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09-03-17, 04:29 PM   #4 (permalink)  
I have a 60-year-old hot-water boiler that runs like a champ. It's a gas-fired, steel fire-tube boiler, and the heat emitters are cast iron. Of course, from that era, it doesn't have a bypass - yet there has never been any condensation problem. It's warm-start, and the aquastat is set for 170 deg. (It doesn't run in the summer.) Now, if I were to install a new replacement boiler, I would definitely include a bypass, but my experience shows that a bypass isn't always necessary.

I have no intention of ever replacing that boiler - unless it splits open. I have a relatively large house, and the annual gas bill for heating is about $1,000.

 
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09-03-17, 05:27 PM   #5 (permalink)  
The cast heat emitters cause the return water to be too cool and cause condensation. The object of boiler bypass is to get the boiler up to temp faster then sitting at the 130f mark trying to get hot..

I would forget about outdoor reset unless you do a mod con boiler..

As far as the other poster with his 60 yr old boiler..

You probably dont have condensation issues because

1. Its a warm start boiler
2. Its a large mass boiler, and has as much water as the heat emmitters.

Todays boilers have only a few gallons in them. Try to heat 3 gallons and send it to a cast iron loop that holds 18 gallons..


Mike NJ




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09-04-17, 02:39 PM   #6 (permalink)  
Several features to consider when buying a non condensing gas boiler replacement.
1. Gas burner with modulated firing rate rather than fixed rate lowers costs.
2. Aquastat with Outdoor reset feature lowers fuel costs.
3. Automatic electric vent stack damper
4. Easy way to avoid condensation (instead of bypass) is with circulator return water low temp cut off set at 137F. It can also simultaneously be boiler safety over temp set at 190F. A $20 ebay PID does both.

High end boilers come with these features but they can be added separately at lower costs.
Features 2, 3 and 4 can also be added to update old boilers. Smaller burner nozzles can increase efficiency of old boilers while still meeting heat load at design outdoor temperatures.


Last edited by doughess; 09-04-17 at 03:06 PM.
 
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09-04-17, 03:21 PM   #7 (permalink)  
Lawrosa: "I would forget about outdoor reset unless you do a mod con boiler."

Noncold start , cast iron non condensing boilers aquastates are commonly set at 180F through out the heating season. That is wasting money except on the coldest design temp days. ODR's adjust the hydronic system water temp to what is actually needed on any given day.

We find the house feels more comfortable with no noticeable sense of change in heat load even on the coldest days.

ODR savings are typically 5% to 15%. For $156 the savings are worthwhile to some Tekmar 256 - Tekmar 256 Boiler Control - One Stage Boiler - Tekmar - SupplyHouse.com

 
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09-04-17, 03:31 PM   #8 (permalink)  
You probably dont have condensation issues because

1. Its a warm start boiler
2. Its a large mass boiler, and has as much water as the heat emmitters.
Both are correct. I estimate the volume of my hot-water boiler to be about 35 gal.

 
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09-04-17, 04:12 PM   #9 (permalink)  
Several features to consider when buying a non condensing gas boiler replacement.
1. Gas burner with modulated firing rate rather than fixed rate lowers costs.
2. Aquastat with Outdoor reset feature lowers fuel costs.
3. Automatic electric vent stack damper
4. Easy way to avoid condensation (instead of bypass) is with circulator return water low temp cut off set at 137F. It can also simultaneously be boiler safety over temp set at 190F. A $20 ebay PID does both.

High end boilers come with these features but they can be added separately at lower costs.
Features 2, 3 and 4 can also be added to update old boilers. Smaller burner nozzles can increase efficiency of old boilers while still meeting heat load at design outdoor temperatures.
Non condensing do not have variable firing rate.. Only one I know. Locinvar. #1 is true.

#2 is debatable. If your talking fixed firing rate I say no. I used more fuel with varied temps of my boiler during shoulder season.

All boilers come with #3 AFAIK

# 4 is again debatable and that was old school thinking in the 60's. in fact old hydrotherms came with that feature. Its a waste of firing in my opinion. Heat up, dump to zone, pump off from cold slug, heat up, dump to zone, repeat..

Best to not have ODR and have temperature control based on T stat input. Like hyrolevel aquastats..


Mike NJ




"The problems that exist in the world today cannot be solved by the level of thinking that created them".


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09-04-17, 06:16 PM   #10 (permalink)  
Lawrosa: "I would forget about outdoor reset unless you do a mod con boiler."

Aquastats on non cold start , cast iron non condensing boilers are commonly set at 180F through out the heating season. That is wasting money except on the coldest design temp days. ODR's adjust hydronic system water temp to what is actually needed. On a warm day water when 140F is adequate it is not heated to 180F. Simple math shows the savings.

ODR savings are typically 5% to 15%. For $156 the savings are worthwhile to some Tekmar 256 - Tekmar 256 Boiler Control - One Stage Boiler - Tekmar - SupplyHouse.com

With ODR we find our home more comfortable with no noticeable sense of change in heat load even on the coldest days.

 
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09-05-17, 02:12 AM   #11 (permalink)  
Doug is theoretically correct in his assessment however Mike is more correct in the real world. Having the boiler maintain the high limit setting (180 degrees) IS wasteful and for that reason I like to see the burner fire from both the room thermostat and the high limit aquastat. The result, if the rest of the system is anywhere near properly designed, results in a system (and boiler) temperature that modulates according to the needs of the home. In warmer weather the system temperature will trend downward and in cooler weather it will approach the high limit. Having a wide "dead band" (differential) setting on the high limit can help. Of course this effect is more pronounced in a high mass system.

As for item #4, remember that Doug is an engineer and he has extensive controls system experience. I DO NOT recommend a layperson do any controls re-engineering without competent assistance. Little mistakes in this area can lead to big problems and huge expenses.

 
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09-05-17, 02:55 AM   #12 (permalink)  
Well yes real world and there are many variables. When I tried to manual regulate my aquastat during the shoulder season It would fire 24/7 pretty much off 140-150f boiler temps. T stat was slow to respond. Hours to raise a few degrees.

This is where I set the t stat and forgot about it the whole season. I used more fuel that year and it was similar conditions the previous year.

Now more variables...

I have a heat loss of 27k btu.. I have a 60 plus year old hydrotherm boiler thats an HC 85K ( DOE may be about 50k btu) I assume when the dead men put it in , it was sized to the baseboard. Baseboard is 40k total..

Holds 5 gallons water or so.. Maybe 8 I cant remember.

Aquastat spread is set rate 15f.

Now my gas bill is 766 $ for the year.. Thats the whole house. Boiler, dryer, stove/oven.

I worked with many engineers and PH'ds. Even the head engineer from weil mclain for a few years..

ODR may look good on paper, but there are many instances it does not work and is a waste of payback on the investment. Im talking fire on/ fire off units.

From my experience with some set ups ODR uses more fuel. Then the cost for the materials to do this on an older boiler.

Mod cons and variable gas valves are a whole other animal, But I will debate the cost of those too and the payback from trying to go green. It will cost you more in the long run..

Just my opinion though.

Ill sell people properly sized on/off systems here in NJ all day in the $5000 range, and they will be happy 25 years down the road. Exceptions are always there though. Space constraints, large familys with HW issues, radiant heat.. etc etc..

I should be in bed.. Insomia for the past 6 months.. Its 5 am... sheesh.. sry if Im ranting....


Mike NJ




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09-09-17, 06:50 AM   #13 (permalink)  
A basic is heating boiler water to 180F uses more BTU's/$$ than to 140F. Properly set up ODR's provide necessary heat/response time at design temperature. In very cold weather I raise my ODR minimum from 140F to 155F.

A basic way to measure boiler/burner efficiency and/or wasted energy is with stack temperature. Higher stack temps are more wasteful. That is why condensing system are more efficient venting at low temperatures.

Longer burner cycles have higher stack temps and lower efficiency. Just plot the temp during a burner cycle and check the charts.

In today's quest for lower fuel costs most boilers have an Out-door-reset option. Unfortunately because some customers want long cycles ODR's have a AutoDifferential option. AD creates longer cycles and higher temp overshoot. With that AD activated my boiler went to 190F + well over the ODR 180F max setting. Now use a 4F delta for 3 minute cycles.

One factor that throws off a systems data is domestic hot water. If it is constant over the heating season (in my home one gallon of oil per week) DHW will decrease degree days per gallon in warmer weather and raise it in cold weather.

Boilers sized many years ago for a home, today are often grossely over sized (85% are twice needed size) because of added insulation, better windows, etc..

Reducing the BTU thru put of a boiler/heat exchanger increases efficiency. Putting a smaller nozzle on a boiler so that it runs 30% of the time on the coldest day/design temp is an easy way to save on fuel costs and still have plenty of heat.

Old timers were told that reducing boiler firing rate is not good. Back then oil burner home fires were were common in suburbia. High stack temps was a way to avoid sooth that clogged boilers and led to fires. The emergency burner off switch at basement entrances was to make life easier for firemen entering smoke filled basements. Around here it has been years since the local fire department reported an oil burner fire.


Last edited by doughess; 09-09-17 at 07:09 AM.
 
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09-10-17, 08:38 AM   #14 (permalink)  
I have a 37 year old boiler which I think is due for an upgrade.
37 years is not all that old for a hot-water boiler. (Mine is 60.)

When you say it's "due for an upgraded," I wonder. If you are wanting to install a more efficient unit, be aware that it's essentially axiomatic that replacing a boiler that works can't be justified, economically with a reasonable payback period, on the basis of fuel savings.

 
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09-12-17, 08:31 PM   #15 (permalink)  
The main operational difference between that 37 year old boiler and new units are 3 simple things that can be easily added to upgrade it. A major advantage of keeping older boiler is they are often easier to clean and maintain efficiency.

1. Out-door-reset / Aquastat – lowers fuel costs $157
Tekmar 256 - Tekmar 256 Boiler Control - One Stage Boiler - Tekmar - SupplyHouse.com

2. Primary Burner control with LCD display that shows status and history to help trouble shooting $60
http://www.supplyhouse.com/Honeywell...ary]R7284U1004 - Honeywell R7284U1004 - Universal Digital Electronic Oil Primary[url]

3. Electric vent damper to cut heat loss when not firing. $169
http://www.supplyhouse.com/Field-Con...per-11822000-p

If you have to eventually buy a new boiler these things can be used on it. Cost will be far less than if purchased with new boiler


Last edited by doughess; 09-12-17 at 08:57 PM.
 
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09-12-17, 11:24 PM   #16 (permalink)  
Doug,
I would like to take these things in order.
1) The boiler being installed only has 2.4 gals. of water. How much heat is it going to take to reach boiler temp. Very quickly I would say. How much can be saved by heating 2.4 gals a few degrees lower. Not much I believe. In my opinion it would take him a lifetime to see any payback.

First off he has cast iron radiators that only need 150 degree water feeding them to get as much heat as traditional baseboard at 180. You can raise the temp for more heat if you need it but rads in a hot water system are figured at 150 deg.

2) That primary control you mention is for oil and he has gas so it doesn't even apply. Why bring it up to confuse the issue.

3) The electric vent damper is standard issue on every boiler and furnace. Again, why bring it up when it is standard equipment. There is a reason why those dampers became standard equipment and it was not to raise efficiency.

There is no way to increase the efficiency of an atmospheric gas burner. There are no adjustments as there are on oil. The gas comes in, goes into the tube burners, brings the unit to temp and shuts down.

I live in MA so I can only speak for that state. Back in the 80's the state said that in order for a gas unit to be approved in MA it had to burn 80 per cent efficient, up from the normal 60's range. Being atmospheric there was nothing that could be done so the 2 parties reached a compromise which was if the manufacturer added the damper to help reduce standby loss they would approve them. It didn't improve the efficiency of the burner, just kept the heat in the unit longer.

The improvements in the units design over time have helped. Smaller units, less water, better design as is tighter boilers and more baffling to delay the heat from going up the chimney. Hence the low stack temps they produce now.

All that being said I think he would be foolish not to put a by-pass in. As I said it takes very little time to heat 2.4 gals of water and the minute that water leaves the boiler and returns cold system water besides you're concerns about condensation how about thermal shock to the boiler until warm water starts returning. With a high mass system you must temper that water coming back to the boiler.

As far as having a control to turn the pump off at a certain temp all that would do is keep that pump cycling on and off every couple of minutes until the system stabilized which is no good for the pump at all.

Something that I didn't see mentioned which I think is important is the expansion tank. With cast iron rads you will want to put in at least an extrol #60 because of the water content in the system. If you go with the #30 you will most likely have pressure problems causing the relief valve to open.

This is just my opinion and I hope it helps a little.

 
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09-14-17, 09:12 AM   #17 (permalink)  
Many existing systems are not cold start and water temp is kept at same temperature, commonly 180F, for coldest design days throughout the season. That adds up big waste which out-door-reset can reduce and is why they are widely used.

Hydronics system water temperature is based on formula to provide necessary BTU's on design days in a given system, not because radiators are made of cast iron. Because of scaling it should not be set above 180F

Stack temp goes up with higher water temp settings. Lowering the water temperature based on outside temperature on gas or oil burner raises efficiency and lowers costs.

The 3 points I raised in another post were to be considered before replacing a boiler. Installing those features now on existing boiler was still usable can bring cost savings for years. Eventually when necessary a new boiler could then be purchased without those items and they could be used on it.

Electric stack dampers reduce latent heat loss. While not on most older systems they reduce fuel costs making them more efficient. May not be "combustion efficiency" but still saves money. Brookhaven National Labs did a major Department of Energy study on latent heat losses in residential systems and found it to be a significant cost factor. My 18” X 6” vent to damper was a “heat pipe” sucking BTU's of the boiler when not running. I wrapped it with $1 insulation.

The smaller physical size of modern boilers make them more difficult to clean and maintain efficiency. Often do not have clean out doors. People who buy new boilers should measure the stack temperature and recheck it over time. There is a good chance they will never get it down to the temp when new. I use stack temp as gauge on when to clean boiler. When necessary just open the boiler doors and clean with brushes. Yes, it has bigger foot print than new one but is easy to maintain efficiency.

My 60 old cast iron boiler is fired at 50% of rated and at 86% efficiency. On design days at 0F it runs 8 hours a day. It is sad to read on DIY about people replacing good working systems for invalid reasons. Unfortunately there is often incorrect data in DIY posts that contributes to it.


Last edited by doughess; 09-14-17 at 11:01 AM.
 
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09-14-17, 07:44 PM   #18 (permalink)  
Spott:
As far as having a control to turn the pump off at a certain temp all that would do is keep that pump cycling on and off every couple of minutes until the system stabilized which is no good for the pump at all.

To avoid condensation, my circulator cut out control activates at 137F once in the morning when room thermostat raises temperature to day time setting. Boiler aquastat/ODR has already started the burner when it sensed a drop in water temperature. There is no repeat cycling of circulator cut out.

Bypass setups mix boiler return and output water sending a lower temperature water to convectors resulting in less BTU's per gallon of flow. How significant that is depends on loop delta T.

The electric circulator cut off is not new. The builder of my 60 year old system installed a Honeywell L4006 ( $80) low temp circulator cut out. An electronic $20 control is cheaper than by pass plumbing. Take your choice.

 
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