Condensing Boiler good for hot water baseboard?

Andrew J. Staves

Hello,

I am in the process of replacing the boiler in my older home. I will be using baseboard hot water for delivery. My question is can I safely use a condensing boiler (LP) for this application. All of the literature I read says they are recommended for radiant systems. I understand they are made more efficient by the lower return temps of the radiant systems but are they being used for typical hot water systems?

The higher efficiency is a plus but my main reason for wanting a condensing boiler is the ability to vent through PVC. The chimney in the house is unlined and in very poor condition.

So... Is a condensing boiler a good option and if so who are the major players? I have looked at the Dunkirk Quantum series but have not found many others. The heat loss calculations for the house came in at 46,000 BTU/HR.

Thanks for any help. It looks as if there is a great deal of knowledge on this board.

R. Kalia_5

You don't need condensing boilers to vent out the side of your house...I understand you don't want to vent through the chimney, but why does it have to be PVC? Won't metal do?

You can use a condensing boiler with baseboard, no problem, but it won't condense on very cold days (when you need very hot water to heat the house) and so the efficiency will be lower. With an outdoor reset controller, you'll use cooler water on warmer days, so you'll get some condensing each season, but probably a noncondensing boiler that vents out the side of your house ("direct vent") is your best option. Look at the web pages for Weil-McLain, Dunkirk, Burnham, etc., etc.

Kal Row

or a slant-fin vsph, most bang for the buck, in direct vent...

however a weil-mclain ultra will cost you the least to run, even though you cant get condensing on cold days when the return temp is above 136f, nevertheless, the high eff combuster and rapid heat transfer of the aluminium heat-ex and it's outdoor rest - will save you a bundel in fuel costs - IT .. JUST .. WILL!!! - you simply have to believe the experiance of many

Ted_9

OR....You can design the system supply water temp lower say 150(example) on the coldest day of the year, use outdoor reset and the boiler will condense almost all the time. This will also give a nice even heat. The only downside is that if your using standard copper fin, you will need more in each room, or you'll have to use a higher output btu copper fin.

You can use the new Slant fin heatloss program to play with design water temp to show you the differance in the amount in copper fin.

Kal Row

i you go that route...

you can take the slant-fin vsph - pipe it into a pri/sec/injection setup with a tekmar 361 (which also gives outdoor reset) - and you will save almost as much as a condensing boiler even on warm days - since the boiler loop will only run about 2 minutes out of 15 on a 40 degree day and the direct vent boiler will hold it's heat - such a setup will be less expensive to install and last longer than a condensing setup - been there done that

Andrew J. Staves

Thanks for all the suggestions. I have a few more questions.

Can anyone point me to a good resource to research the primary/secondary injector option?

Are the condensing boilers prone to failure? Someone mentioned that a non condensing boiler would last longer.

Thanks again for all the help. This forum is a great resource.

Andrew J. Staves

Thanks... more questions

Thanks for all the suggestions. I have a few more questions.

Can anyone point me to a good resource to research the primary/secondary injector option?

Are the condensing boilers prone to failure? Someone mentioned that a non condensing boiler would last longer.

Thanks again for all the help. This forum is a great resource.

Floyd_5

One question......

How long DO you want your boiler to last???????
Sorry two questions......:-)
What will be out there to heat your home with in say fifteen years????

Think about it....

Floyd

Andrew J. Staves

How long will it last

Well... if I can buy a lower efficiency unit that will last twice as long there may be no savings in the high efficiency unit... right?

Floyd_6

Uhhhh... I think that my point......

flew right on by you.....

Have you given any thought to the fact that there may be units out there that in fifteen years, will have pushed the envelope BEYOND the 100% barrier?????
One poster here has clocked his boiler at or very near 100% eff. already!!! In 15 yrs. you don't think that those numbers can be improved upon????
What other alternative heat sources may be available in 15 yrs???? Will petro products even be available on a large scale in 15 yrs????
Whodathunk that I'd be typing away on a 'puter that can perform the many functions or even a fraction of the functions that these machines are capable of 15 yrs ago????
How many people were doing P/S piping 15 years ago???
Look at the strides made in radiant technology in the last FEW yrs!!!! AND there are still many areas of the radiant field that are yet to explored.........
My point is... for what it's worth.... that the so called high eff. mod. 90+ boilers of today, may well be totally outdated and not even something that you want to have in your house in 15 yrs., so why worry about a boiler that may last forty years, by then the old fossil fuel, energy wasting 80% boiler may be ILLEGAL!!!!
For ME, give me the most eff., thing on the market that will give me 15 yrs. of service.... by then I will be wanting to install the next latest and greatest thingy that has beeen dreamed up, anyway.
Hopefully something that uses the good old sun and a PV array so we can tell all the other countries that have been living high in the hog from us for so long to "take their oil and shove it!!!!"

Okay, better shut up.... I'm getting too wound up and I have to get some shuteye......

Floyd

Darin Cook_3

Got to agree with Floyd

A condensing boiler on its worse day is still head and shoulders above a cast boiler on its very best. Hold your hand in front of a cast iron boiler flue, then in front of a condensing boiler flue. The reason your hand turned into a piece of charcoal on the cast flue is all the money going up the chimney disguised as heat burned it. You can hold your hand in front of the condensing boiler all day. That is why it can be vented with pvc. As far as the boiler running above 150'. We have more time in the shoulder seasons than we do with worst case design day. Go with the condensing boiler. Your wallet will thank you.







Darin

Plumbob

cold days vs warm days

> As far as the boiler running above 150'. We

> have more time in the shoulder seasons than we do

> with worst case design day. Go with the

> condensing boiler. Your wallet will thank

> you.


You may be right about the conclusion, but I would question the data. Of course you have more TIME in shoulder seasons. but do you have more DEGREE-DAYS, and if so how many? I mean, in our area we have many heating season days with 20 or 30 degree-days per day, but a design day is 75 degree-days, so in terms of fuel consumed it counts as much as 3 or 4 typical heating season days.

My guess is that something like 1/3 to 1/2 of the heating season's gas consumption will be in noncondensing mode with our boiler. But that depends on the radiation in the house so it's not a general rule.

Darin Cook_3

Something to keep in mind

You can program the delta T you want into the boilers logic. You will be operating on a outdoor reset curve. The boiler will modulate itself down as it approaches the programmed limit. These features will help squeeze quite a few more dollars out of the fuel. There is nothing wrong with CI boilers, I have installed many of them. But I feel the energy tweeker is hands down the condensing boiler. Mr. Kalia has my gotten curiosity up now. I will have to look up what the degree days were for last winter, spring, and fall. I believe the numbers will favor the condensing boiler. I will post back what they were for my area.






Darin

DaveGateway

Condensing at 160°

claims Dunkirk on the Quantum Leap boiler. If the secondary heat exchanger can pull enough heat out of the water, you'd still see some savings with BB. Now will you recoup the added cost of the boiler over 15 yrs is the question.

Boilerpro_3

My experience with the Quantum

is that the exhaust temp is typically about 10F below the return water temp. The secondary "ecomnomizer" heat exchanger pulls heat out of the exhaust air and transfers it to the very cold intake air...thats how they get condensing at higher water temps. It's your basic industrial stack econmomizer concept just tweaked some.

Also I have found very few baseboard systems need above 160F supply/ 140f return on design days due to excessive system capacity. Measure up your baseboard capacity and check it against your load.

Here's how much condensate my Quantum made in one hour at a steady 140F supply and 120F return (about a typical midwinter day operating temp for a 180F baseboard system with outdoor reset).

Boilerpro

Rick_17

was the amount of concentrate considered a good amount or less than normal? I am guessinga good amount

Kal Row

http://www.tekmarcontrols.com/literature.html

also if you really want to learn -
dna holoan's books and video's on this site
and siggi's book and software at hydronicpros.com



being that weil-mclain ran the ultra in the lab for 15 years under stress - like double pressures and cold shocks - befor they let the secret out - i expect it to live for 30yrs in the avg home - but based on the current gas price rising curve, you will probably chuck it in 7-10 for something with just 3points more effciency

Kal Row

goto...


http://www.tekmarcontrols.com/literature.html

also if you really want to learn -
dan holoan's books and video's on this site
and John Siegenthaler's (aka siggi) book and software at hydronicpros.com



being that Weil McLain ran the ultra in the lab for 15 years under stress - like double pressures and cold shocks - before they let the secret out - i expect it to live for 30yrs in the avg home - but based on the current gas price rising curve, you will probably chuck it in 7-10 for something with just 3points more efficiency

EG: we now have solar concentrators – long solar tubes with water at 1/3rd atmospheric pressure that boils with even low sunlight and condenses at the top and produces a hot point – this so-called “leverage action”, that of exchanging distance for force, or, in our case, a large low temp area, for a small hi temp area, – has not even be scratched on by the boiler manufactures, but, when gas is 5 times what it is now, they will, and boilers, instead of becoming smaller – will become much larger – we may be using fuel cell type of catalysts and heat concentrators – who knows?

Christian Egli

Stoicheiometry

Dear Boilerpro,

Your idea to collect and measure the condensate from the flue was simply brilliant. I wouldn't have thought of it, all that pure natural water ready for quenching your thirst...

Anyway, the data gave me plenty fun. Here is what I was interested in figuring out: condensing boilers boost efficiencies, but only when condensing; it is obvious they don't always condense nor do they either condense everything there is to condense. I wanted to figure out the size of your boiler, by assuming it was working at full efficiency, from the amount of flue juice you reported.

From the chemical combustion process it is easy to determine that for every 36 weight units of water that was produced, 16 units of natural gas would have had to be burned. I saw 7 cups of fluid on your boiler that you collected in 1 hour, that means that you had to be firing at least 38000 BTU/h. That's the minimum needed to produce 7 cups of moisture in an hour, operating at the most maximum possible efficiency.

I am sure your boiler is much bigger than that. If it is 100000 BTU/h, about three times bigger, it would mean that about 2/3 of the combustion is not benefiting from the condensing feature. I am guessing that thermodynamics make it impossible to get that far anyway.

Next, from knowing what condensate in steam heating represents in heat value (1 GAL of condensate is rendered for every 8000 BTU) the 7 cups of flue juice represent a bonus heat of 3500 BTU that you recuperated. It does not seem like much.

In value, if you pay your gas 1 $ per CCF (100 ft3 or therm) the recuperated bonus heat nets a saving of 3.5 cents. Really not much! I was disappointed, I thought we should all have been millionaires by now. If you have a 100000 BTU/h boiler, you'll be burning gas at 1 $ per hour. Consider though, that 3.5 cents on the dollar is a much better return than what most banks pay today. So money in the boiler is better placed than in the checking account! That seems twisted!

Taking an input of 38000 BTU/h would leave you with 30400 BTU/h net from the combustion (80% efficiency like any non condensing boiler) add to that the recuperated bonus heat, 3500 BTU for 1 hour, you get 33900 BTU/h net output with the total condensing feature. That's 89 % efficiency on the input. Quite nice.

If I guess that your boiler has an input of 100000 BTU/h, you will get 80000 BTU/h net of any condensing feature, add the bonus and you get 83500 BTU/h net output or an efficiency of 84 %.

Impressive results, but not as promised as on the brochures I am sure. The difference which I did not account for most certainly comes from the removal of the standing pilot light, and better jackets.

Should we always believe glossy brochures? Well, for instance, old steam boilers that were meant to burn coal or wood or whatever were reported at 40 - 70 % efficiencies; that was true for those fuels that are only burned with lots of excess air (excess air, means excess inefficiencies) but converted to modern gas and correct excess air their efficiencies probably reach efficiencies we find normal today.

Boy, it sure seems I could write my own glossy brochure. Anyway, you'll see how I entertained myself today.