Indirect vs. Standalone

Reply

  #1  
Old 12-13-07, 06:26 PM
G
Member
Thread Starter
Join Date: Dec 2007
Posts: 4
Received 0 Votes on 0 Posts
Indirect vs. Standalone

Just came accross this site and read through quite a few threads. Some really useful info and obviously talented individuals contributing, thanks in advance.

My ? - I need a new boiler and two qoutes also included replacing my seperate 9 year old 40 gal gas fired hot water heater (dwh?) with a similar (though newer) model.

I read a number of threads about Indirect, and looked at options form the manufactureres (weil mclain and burnham).

Is it really more efficient to run my boiler year roud with an Idirect to heat my hot water than to have a seperate unit? (I sense from the popularity among the pros here the answer is yes, but wanted to make sure).

BTW, one quote was for a 105btu unit and the other for a 135. Interesting how far apart these guys can be . Fortunately I read the threads about proper sizing.

Thanks Much
 
Sponsored Links
  #2  
Old 12-13-07, 07:06 PM
Who's Avatar
Who
Who is offline
Member
Join Date: Jan 2006
Location: San Jose
Posts: 2,175
Received 0 Votes on 0 Posts
If you get a modcon and an indirect, that's as green as it gets for heating water short of solar.

What's your heatloss?
 
  #3  
Old 12-14-07, 06:00 AM
G
Member
Thread Starter
Join Date: Dec 2007
Posts: 4
Received 0 Votes on 0 Posts
Thanks who. What's a modcon? My heatloos is around 57-60,000 depending on what I use for the infiltration number.

When I bought the house 18 yrs ago my egineer told me the 145k Hydrotherm unit was more than it needed, but I thought that was a good thing
 
  #4  
Old 12-14-07, 06:30 AM
X
Member
Join Date: Nov 2005
Location: USA
Posts: 2,459
Received 0 Votes on 0 Posts
modcon = modulating/condensing boiler. The modulating part means they can adjust their heat output according to outdoor temperature. The condensing part means that if return water temps are low enough, latent heat of condensation is released and utilized in the heat exchanger, giving efficiencies well into the 90s%.

Some brands, in no particular order:

Triangle Tube Prestige
Lochinvar Knight
Buderus GB142
Weil-McLain Ultra
Burnham Freedom and CHG
Viessmann Vitodens
HT Products Munchkin

If you're going to be in the house a while, and you are a candidate for a boiler replacement, then a modcon is definitely worth a hard look. Payback on added cost is getting pretty short in these days of increasing fuel costs. My personal preference is for models with a stainless steel heat exchanger. I think there is still much to learn and adapt to where aluminum block heat exchangers are concerned. Keep in mind that these are not your father's boilers (a large hunk of big, thick cast iron with simple controls that might last 30-50 years). They are microprocessor-controlled, reasonably high tech pieces of electronics that do a lot of tweaking to firing rates, fan speeds, etc. and utilize some fairly lightweight components. You can plug your PC into them!

You'd be a good candidate for an 80k modcon and an indirect in the 40-50gal range, assuming you have "typical" DHW needs. A modcon is definitely a very efficient way to heat your DHW. Also gives your boiler something to do during the summer so it doesn't sit around bored, rusting, etc.

More indirects to look at:

Triangle Tube Phase III
HT Products SuperStor
Crown MegaStor
Buderus ST-xxx
Weil-McLain
 
  #5  
Old 12-14-07, 11:58 AM
G
Member
Thread Starter
Join Date: Dec 2007
Posts: 4
Received 0 Votes on 0 Posts
Thanks for the explanation Xiphias. It looks like most manufacturers are using the aluminum exchanger. I only saw the SS in the Knight and Viessman models.

It also looks like this class boiler (modcon) is about $1200 more than conventional, and the indirect tank about $500 more than a seperate water heater. When I look at the energy savings on a 95% AFUE over my current 65%, it looks well worth it.

Any idea how long these modcons will last? Looks like shorter warranty's from the manufacturers (Weil Mclaine). Though some of the indirect units come with a lifetime one (seems reasonable for a tank!)
 
  #6  
Old 12-14-07, 06:02 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Posts: 2,482
Received 5 Votes on 4 Posts
Bear in mind the mod/cons are not always 95% efficient. This is a big misconception by homeowners. They can operate anywhere from 98% down to 85% dependent on the application. I am not saying they are not good products. They are. In proper applications they are as efficient as you can get. In other applications they are not much more efficient than the cast iron products. This is assuming all are properly sized and piped and not including chimney vented products. Chimney vented products are the least efficient as the chimney draft continually steals heat from the boiler increasing standby loss up the chimney.
When looking at a boiler purchase it may not be a good application when looking at your financial situation. When the finances allow the mod/cons can be the best choice. Mod/cons can save a lot of money over cast iron boilers or just a little bit. They do require more maintenance including servicing every year. This is a must. Cast Iron equipment also require annual maintenance but less time consuming at a given hourly rate. Replacement parts for mod/cons can also be more expensive. The cast iron boilers have a longer warranty, which may be good or bad. I say that because do you want the same boiler for the next 30 years. Probably not, as fast as our industry is changing. The biggest fuel savings today is proper sizing, proper piping and outdoor reset.
As far as stainless steel or cast aluminum which is best? They both have good points and bad. The main points is the stainless steel if more forgiving in PH issues. The stainless depending on design may be more restrictive. The aluminum transfers the heat a lot better then stainless. The antifreeze for stainless is cheaper.
 
  #7  
Old 12-14-07, 09:35 PM
Who's Avatar
Who
Who is offline
Member
Join Date: Jan 2006
Location: San Jose
Posts: 2,175
Received 0 Votes on 0 Posts
GoFsh, I probably spent about 3 years trying to figure out what I wanted as a replacement boiler. I ended up getting a Prestige installed pretty well exactly a year ago. My heatloss was almost identical to yours although I find out a few weeks after installing it that my true heat load was actually just under 40 MBH. "Manual J" calculations are way too conservative.

Nice and quiet boiler, especially since it only operates at its lowest end given the heat load. It's a robust simple design with a low head self-cleaning stainless steel heat exchanger. It has a built in pressure switch that satisfies most jurisdictions requirements for a low water cutoff device and also has a well proven controller that is used by Weil, Burnham, ECR, and even big commercial units like Cleaver-Brooks Clearfire. It also has a built-in 3 speed and can be piped direct if that's beneficial. It's built by ACV of Belgium and has an excellent reputation in the market place.

The savings on a modcon is far more than the difference between say 87% and 92% - probably something like 25-35% better savings, especially in the shoulder seasons. With my crappy fintube and a current outdoor temperature of 18, my boiler only has to get up 126 on the supply side and the exhaust temperature (where the wasted BTUs go is only getting up to 114 tops). Compare that to a conventional boiler with a stack temp of 325 or higher, unless it too is condensing. Unfortunately, low temps in the returns and flue will kill conventional stuff while a modcon works best that way. I disagree about the difference in servicing. Compare a modcon to a power vented boiler with ODR to keep it apples to apples and it stays apples to apples.
 
  #8  
Old 12-17-07, 02:53 PM
G
Member
Thread Starter
Join Date: Dec 2007
Posts: 4
Received 0 Votes on 0 Posts
Another Quest. - Does a Modcon benefit from an ODR?

Just got off the phone with one of my vendors and he said Indirect is not more effiecient in the long term a seperate 40 gal gas fired is. Not sure I agree with him. Anywho...

My gas co (Keyspan) is offering $500 rebate for upgrading to 85% AFUE, and $800 for 90%. They're also offering $300 for indirect, and $100 for ODR, woo hoo!

My cost (from one supplier) is $850 more for PVG (85%), $800 more for indirect???, and $600 more for ODR (seems high)

I'm thinking I add the ODR afterwards and look for a better price, though the gas savings seem potentially worth it. Any advice?

Thanks
 
  #9  
Old 12-18-07, 12:03 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Posts: 2,482
Received 5 Votes on 4 Posts
Who,
The fuel savings is not much more than the difference between an 87% and a 95%. The 25-30% you state is a total fuel savings between a new boiler and an old boiler. This takes into consideration of all the changes. They will both save about the same amount. True the mod/con will be slightly better as the efficency is slightly higher. Any boiler job properly sized and piped should save on average between 25% and 50%. I have seen numbers as high as 74% (cast iron boiler installation). This number does not change a lot between mod/con and standard cast iron. Again there will be more savings with the mod/con (dependent on water temperature during most of the heating season) as it condenses. A bigger savings could be picked up by the cast iron boiler if two stage outdoor rest is used. Stage one starts the circulator and stage two starts the burner. This brings the savings closer to the mod/con boiler.
A lot of the power vented cast iron equipment will operate in the 250 range. That is the reason for stainless steal vent pipe. Again this conversation does not apply to chimney vented products.
 
  #10  
Old 12-18-07, 12:50 PM
Who's Avatar
Who
Who is offline
Member
Join Date: Jan 2006
Location: San Jose
Posts: 2,175
Received 0 Votes on 0 Posts
Who,
The fuel savings is not much more than the difference between an 87% and a 95%. The 25-30% you state is a total fuel savings between a new boiler and an old boiler.
rbeck, my belief is that the difference in AFUE on new equipment is far more than what the AFUE numbers state. I should have stated that was my opinion and not tossed it out as fact. When comparing old equipment to modcons, my opinion would be that it would be even higher.

I would love to see the NRC's twin test houses in Ottawa set up with panel rads instead of a forced air system and then they could do a scientific comparison there at different outdoor temperatures.

In the absence of science we are left with opinions...
 
  #11  
Old 12-18-07, 01:53 PM
M
Member
Join Date: Oct 2007
Location: Eastern CT
Posts: 150
Received 0 Votes on 0 Posts
I see the chimney vented is a definite liability... What is normally done if you upgrade to a mod/con or power vented and your old set up was cheimney vented? Do you have to put a new ole in the basement wall or run pipe up through the chimney? Is a 2 stage reset wothwhile for an older (oil fired) boiler? Does this take the place of the conventional aquastat?
 
  #12  
Old 12-18-07, 02:06 PM
Who's Avatar
Who
Who is offline
Member
Join Date: Jan 2006
Location: San Jose
Posts: 2,175
Received 0 Votes on 0 Posts
Mike, when I replaced my old conventional boiler, I had the contractor run the PVC venting up through the clay-lined chimney and terminated about 18" above the top. Some manufacturers/contractors will poopoo that set up because of potential imbalance issues from where the intake piping is located compared to where the vent is exhausted. On the other hand, it does eliminate the risk of sucking corrosive exhaust gases into the boiler.

Sidewall venting was not an option I wanted to explore. If you do have to vent through a sidewall, consider that you may end up with considerable icing happening there.

Any modcon venting that I have seen the vented vertically out of a chimney has not had ice buildups near it.
 
  #13  
Old 12-18-07, 03:19 PM
rbeck's Avatar
Member
Join Date: Jul 2007
Posts: 2,482
Received 5 Votes on 4 Posts
I hope you did that before July when they passes the 626code in Ontario. Of course I understand you could use IPEX PVC now. I heard it is a lot more expensive than standard PVC. Is that correct? The new code requires only certified vent material if I understand it correctly. I am sorry I did not follow that code close enough, that is why the questions.
 
  #14  
Old 12-18-07, 04:53 PM
M
Member
Join Date: Oct 2007
Location: Eastern CT
Posts: 150
Received 0 Votes on 0 Posts
Unfotunately my fireplace uses the same chimney so plastic would not do unless I brick up the fireplace...
 
  #15  
Old 12-18-07, 07:45 PM
Who's Avatar
Who
Who is offline
Member
Join Date: Jan 2006
Location: San Jose
Posts: 2,175
Received 0 Votes on 0 Posts
Originally Posted by rbeck View Post
I hope you did that before July when they passes the 626code in Ontario. Of course I understand you could use IPEX PVC now. I heard it is a lot more expensive than standard PVC. Is that correct? The new code requires only certified vent material if I understand it correctly. I am sorry I did not follow that code close enough, that is why the questions.
My install was mid-December last year, and the 636 code went into effect in Ontario March 1, 2007 - this year. It wasn't even stocked back then even though there was awareness that it might be code for January 1st. We used some very nice dark gray USA-made Harvel PVC. The Harvel venting itself was quite expensive.
 
  #16  
Old 12-19-07, 04:08 AM
X
Member
Join Date: Nov 2005
Location: USA
Posts: 2,459
Received 0 Votes on 0 Posts
Originally Posted by rbeck View Post
Who,
A bigger savings could be picked up by the cast iron boiler if two stage outdoor rest is used. Stage one starts the circulator and stage two starts the burner. This brings the savings closer to the mod/con boiler.
I assume that this strategy presumes a well-protected CI boiler (say p/s), and that there is a fair volume of water in the system? For the latter, I can imagine a scenario where the distribution piping would have a comparable volume to the heat exchanger/primary loop, and thus the available heat in the first stage would quickly be exhausted (a minute or two??). Probably truer at cooler supply temps than warmer. Am I thinking about this correctly?

[And wow, talk about thread drift. But a neat topic!]
 
  #17  
Old 12-19-07, 04:55 AM
rbeck's Avatar
Member
Join Date: Jul 2007
Posts: 2,482
Received 5 Votes on 4 Posts
You are right. I have used this application on radiant floor, the Burnham Revolution, which has built in boiler protection down to 55, sealed combustion (250f) vent temp, 87% efficient, concentric vent and two stage outdoor reset. With the water volume and stored energy in cast iron, in the shoulder seasons the system has called for heat in the primary loop up to 3 times as zones are running and the boiler never fired. In the colder times it may or may not fire the first call. It will definitely fire the second call. One thing this guarantees is longer boiler run times, maximum efficiency and no need for added boiler protection.
 
  #18  
Old 12-19-07, 06:55 AM
X
Member
Join Date: Nov 2005
Location: USA
Posts: 2,459
Received 0 Votes on 0 Posts
Interesting. I would have thought the reverse would be the case. Maybe I'm not thinking through all the way, my mixing examples are way wrong, or I don't understand how the staging actually works.

In warm weather, on a call for heat the cooler return temps would rapidly drop the primary/hx loop temp to the point where the burner would fire. Say 80F return water mixing with 190F in the primary/hx yields ~135F and the burner fires. But you get a pretty long burn because the injection rate is low while the primary/hx loop recovers.

In cold weather, on a call for heat the return temp would be hotter and so the primary/hx temp drop would be less and the burner might not fire. (120F return mixing with 190F primary/hx yields ~155F).
 
  #19  
Old 12-19-07, 07:38 AM
rbeck's Avatar
Member
Join Date: Jul 2007
Posts: 2,482
Received 5 Votes on 4 Posts
Aaaahhhhhh!!!!!!!!!!! the beauty of cast iron and water volume with proper sizing piping and control strategy
 
Reply
Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
 
Ask a Question
Question Title:
Description:
Your question will be posted in: