A heating question for all people of the Wall

S Ebels · January 2006

You really don't want to google the word modcon. I just about puked.

Darin Cook_2 · December 2005

There have been alot of comments about condensing

modulating boilers and the if there is any savings(benefit) on using them in a "high" temp application such as fin tube baseboard. I am curious as to what everyone thinks. I want to hear what others both contractors and homeowners have to say about this. I would appreciate anyones input.

Darin

Tony_23 · December 2005

Most of mine

Have been retrofit jobs on existing bbd systems. The avg savings in fuel, as far as I can tell, seems to be 40% a year. Some more, some less. Depends on the HO's habits and lifestyle.

chuck shaw · December 2005

You many not

get the full benefits of the "condensing" action of the boiler, but the lower mass and modulation feature are sure to be of some benefit to any system.

Chuck

Cosmo_3 · December 2005

An analogy

A condensing boiler, coupled with a fully modulating burner gives your heating system a "gas pedal". Think of when you are in your car driving on a long highway with the cruise control set to 65 mph. When you start going up a hill the car's gas pedal is pushed down sending more fuel to the engine to create the increased power needed to maintain 65.

A mod/con boiler with an outdoor reset is similar. Your thermostat is the cruise control. You set it to 70 F, and as the temperature outside goes down (think of the hill) the boiler's computer increases fuel to the burner to give more power to your heating system. It is very smooth, and you don't use more fuel than you need.

A standard bang on, bang off boiler simply gets a call for heat from the thermostat and lights up the burner at full throttle and burns like hell until the boiler's high limit shuts the burner down. That is like stop and go driving when your late for an appointment!

Even though a mod/con boiler will give the best system efficiency with low water temperature heat emitters, when you use an outdoor reset control you will still see fuel savings compared to a bang on, bang off boiler even with a buffer tank.

Cosmo Valavanis

Dependable P.H.C. Inc.

TK03 · December 2005

Mod/Con boilers

When controversial questions such as this are asked you will get every answer imaginable, so let me give you my two cents worth. The most important part of the job in my opinion is the boiler sizing and system piping. I have been on jobs where the boiler was the wrong size or the piping was incorrect and the customer did not save as much as they could have. I have talked to guys that use p/s piping close spaced tees on every job. Not always a good idea if the system is broken down into multiple zones and the loop temp drops temp beyond each set of closely spaced tees. I hear fuel savings of 40% with mod/con boilers. That is not uncommon with standard boilers and all high temp/high water volume systems. I will agree more often with cast iron rads than baseboard. Before I used mod/con boilers I saw an average fuel savings with standard boilers of about 25-40%. I started using the heat manager and saw usually about 30-50%. I calculated fuel savings per degree days. The oil accounts made that easy. I deliver the fuel and know deliveries. The gas units I used total bills, including all surcharge and use taxes. The mod/con boilers I installed were about the same savings. I do not see a lot of difference. Every job gets a heat loss done. All installations get proper near boiler piping including boiler bypass (cold return to hot supply) on the cast iron boilers. Avoid using chimneys on as many occasions as possible as chimneys are heat thieves.
With all low temp systems mod/con hands down (new construction).
Well that my opinion on the situation but than I am one of many options. I just look at the true numbers as I see them.

gasfolk · December 2005

Have found very little direct comparison data.

I'm a mere HO (planning an upgrade). Many credible sources suggest that better part-load matching will significantly improve performance *at any temperature*--even more so if the existing unit is oversized. I have not found hard numbers or direct comparisons because modulating units are typically installed with improved control strategy, outside air for combustion, buffer tank, etc. Apparently, current research at Brookhaven may yield a practical formula for estimating part-load efficiency. Will the cost/benefit ratio of that improvement significantly exceed the benefit of adding a large buffer tank (to reduce short-cycling losses) or a tiny front-end boiler for even better shoulder season load matching? Perhaps the best a HO can do now is find a pro who can walk you through the alternatives and limitations of every system.

Tony, I wonder whether, from your experience with neat replacements, you might offer a rough magnitude of benefit for any these various interventions?

Thanks.

gf

db_5 · December 2005

BNL report link...

Darin,

Here's a link to a BNL study concerning baseboard /
condensing.

I have to go back and reread it, however I believe it
squares with the idea of ( where possible ) running
longer base board at lower temp, say 140*.

I think a higher delta - t figures in there as well.

http://www.osti.gov/energycitations/product.biblio.jsp?osti_id=15010018

Cheers, db

leo g_13 · December 2005

question to Tony

Just wondering, are most of these boilers you are replacing with the mod/cons, right sized? just oversized? or way oversized???

I find that in most of these change outs that I do, the boilers that I replace tend to be 20-50% over sized. So theorectically, just by putting in the right sized boiler, I am already "saving" the customer anywhere from 10-30% on fuel use. Ada a proper tekmar style control, and of course then I can get into the 25-50% range.

I still feel that one point that keeps on not being discussed in these sessions is the "life" of a mod/con to a standard boiler. Really, it shouldn't be an issue, if these M/C's get annual servicing, but as most of us know, A LOT of clients never think about servicing until their boiler is no longer working.

So if these mod/cons are being replaced every 10-15 years and the cast iron ones every 25-40 years, is there really;

a)ROI

b)ecological savings

c) best case for our clients

Let me finish by saying that I have used mod/cons in high heat apps, and will continue to do so if the app is appropriate.

Leo G

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Uni R · December 2005

ModCon/BB

I wonder if everyone here realizes that modcon takes on a very strange context outside of the HVAC world... anyhooooo.

I have fintube baseboard and an old cast iron oil-fired boiler and it will definitely be a modulating condensing boiler when it gets replaced. Better comfort, performance, efficiency...

Tony_23 · December 2005

as always

In answer to your 1st question, "all of the above"

I do a heatloss and size the mod/con to design temp diff. The fact that it modulates makes it "right sized" damn near all the time, doesn't it ? The reference to cruise control in another post is the analogy I use most frequently. Anybody who sets up a mod/con to run up to limit on every call for heat is misapplying the equipment and cheating their customer out of fuel savings. If you can heat the hose with 120 supply today, why aren't you ?
The notion that bbd ONLY works with 180 deg water is ludicrous. I have designed bbd zones into a system with RFH to operate at 130 maximum supply at ODT. They work fabulously and efficiently.
One of the big differences between low mass mod/cons and high mass CI boilers is thermal transfer efficiency. I'll take the aluminum boiler any day in that race.
I also know that part of my experiences in fuel savings ARE outdoor combustion air sealed to the unit, and ODR, and better piping arrangements. Why would you install one of these without upgrading ? A mod/con install is not the place for a wham-bam between the valves swap-out. The only time I leave out the ODR is people who INSIST on DEEP setbacks nightly. That ends up being setback most of the day

Since I don't have a lab or a gov't grant, I just have to rely on my customers' reports. And believe me, they DO report.

gasfolk · December 2005

Totally agree,...

and for the reasons you give, exploration (such as a head to head comparison) isn't likely except from a research lab. A homeowner often must simply ask someone with your experience and credibility which devices and modifications are likely to pay off.

In other threads (particularly those regarding short cycling of oversized, non-modulating boilers), some have suggested substantial improvement in efficiency of old equipment using buffer tank, improved controls, and longer burns. Hence the curiosity whether, in your experience, the fractional contribution of condensing/modulating boilers could be ball-parked, and you've answered that. Thanks.

leo g_13 · December 2005

db, from

what I gather from this report, the boiler used, Monitor, was NOT a modulating boiler, correct?

Would be very interesting to see the results if a modulating boiler was used. Coz I personnaly feel that it is more the modulation that is the "real magic" in these boilers.

Leo G

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Mad Dog_2 · January 2006

Its just common sense to me

If the bb is plentiful enuff to emit sufficient heat at lower temps, there will be savings. Mad Dog

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clammy · January 2006

so far

So far i have about 6 munchkins out there 3 on baseboard 1 on gravity conversion and one on a mix of baseboard and hydroair all with vision one controls and i have heard from the HO that the gas useage was down for the summer i would gather because of the use of indirect water heaters and was also lower for the fall and early winter and since the cold wave of last all stated there therms used where less then the perveous years use .So in all i would have to say that in a high temp sitution that mod ,cond boilers do work .On another note some of these homes need chimmey work or new chimmeys to boot so a direct vent unit like a munchkin fit the bill plus they are much quiter then say a direct vent cast iron boiler and then you got make air to think about to ? But as with any thing you have to do your home work to make sure things will work at lower temps espically with basboard .Peace clammy

Steamhead (in transit) · January 2006

The only problem I have with these units

is that, with the exception of the Monitor FCX, they're all gas-fired. The way BGE has been gouging their customers this winter, I don't see any reason whatsoever to connect more people to their de facto monopoly.

On the oil side, it looks like we'll have to wait for low-sulfur oil sometime this year or next, before we see much more efficient boilers.

This is one reason I haven't retired my V-14.

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Darin Cook_2 · January 2006

The reason I put this post up

is because I see alot of people here make statements to the effect that if a system is "high temp" you might as well be using a CI boiler. There will be no savings using a condensing modulating boiler. I have found this to be completely untrue. The modulating feature especially when combined with outdoor reset, will run circles around a standard CI boiler with a bang bang control approach. Therms used per HDD have consistently been in the 30% - 45% savings range sometimes higher when we have changed the old heating unit to a new condensing,modulating boiler. Switching to a quality indirect WH over a standard tank type atmospheric WH will boost the savings even higher. Whole house efficiency goes up with the reduction of air infiltration required for the old burner operation. Of course plugging off that big hole in the house that was the chimney helps in many aspects.

But in regards to my main point a modulating, condensing boiler has a place in any home for any application. Because it is still the most efficient appliance whether it is a radiant slab or fin tube baseboard. The numbers produced by our customers prove it. Thanks to all who commented here.

adayton_2 · January 2006

MODCON V

! ! ! O U C H ! ! !

A heating question for all people of the Wall

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