installing condensing boiler?..or not

[Deleted User]

Can i install a condensing boiler in a system that is all cast piping and rads?If so will it be worth the investment and how do i make sure it will work well and for a long long time?

Ironman

Absolutely

1. Do a heat loss calc. Size boiler accordingly, not according to old boiler. If you have and indirect water heater, that must be considered in boiler sizing.

2. Measure the square footage of EDR and calculate their capacity.

3. Use Primary/ Secondary piping to keep the flowrate right thru the boiler.

4. Adjust the reset curve according to 1 & 2.

5. Size zone pump(s) for 20deg. delta T.

6. Insulate those large iron pipes in the basement.

7. Seal envelope of house as best you can.

8. Use a good air separator (not a scoop) and a return line strainer at boiler.

9. Flush old pipes well, fix any leaks including valves.

10. Follow manufacturer's instructions: they write them for a reason.

These are not necessarily in order.

Brad White

Ironman has it

The only refinements I would add are optional but helpful:



11. Install thermostatic radiator valves (TRV's) on the CI radiators, especially in rooms that see a lot of sun, bedrooms (where some people like to "sleep cool" and spare bedrooms, (because grandma comes but once a year or because you want to move her along). You can skip bathrooms in most cases, never warm enough, but otherwise, all radiators if you can.



12. Strainer is good on an old CI system and flushing is essential. Using Rhomar products has worked well for me. Stray iron has an affinity for stainless steel, so cleaning that out is not wasted effort.



I use a Neptune filter feeder, 2-gallon, with fabric filters down to 5 microns. I toss a few rare earth magnets in the bag to harvest stray iron particles. After a few weeks they look like little Chia pets.



Lastly, I would not up-size the boiler for the indirect. The time the boiler takes to heat the water, even on the coldest night, is maybe 20 minutes from a cold start. The CI radiator, system and water mass will easily carry you over that period without your noticing.  Chances are your boiler will have some "margin" to the capacity increment size compared to your heat loss anyway. I would not up-size the boiler in your case.



But Ironman's Ten Commandments will serve you well. Good stuff.

Mark Eatherton

Curious ....

Why "not a scoop"?



I've only been using them for 35 years, and never had an issue...



Truth be known, the O2 content of the system, if taken too negative, WILL balance itself out, one way or another. Even with an all metal system it is virtually impossible to keep mother nature from doing her balancing act. Oxygen, like heat, pressure and temperature, flows from areas of high concentration to areas of low concentration.



Unless the fluid is being circulated 24/7/365, you will not be able to keep all oxygen out of the system.



Now, free air on start up is another thing, and MBR's do a great job of removing that, but so do scoops, assuming all of your other components are in the right place in relationship to each other.



Cost wise, MBR's are 8 to 10 times as much money as a scoop.



I'm a scoop man. Can you tell :-)?



ME

MikeyB

System volume

Great points by all, and dont forget to add the right size bladder tank, sounds like that system might have alot of water in it

Brad White

Another

good point, Mike- A typical single-family home gravity HW system has, in my experience, 50 to 75 gallons. (I am about to drain down mine for the first time since owning it, so let's see if the tradition continues... I have two 42 gallon barrels and no basement drain



By contrast, a typical small-tube copper system often has 20 to 25 and most of that in a CI boiler...

So the expansion tank volume must take this into account.

Ask-me-how-I-know...

NRT_Rob

air seps

guarantee no air problems in almost all circumstances. Low flow velocities, bad purging, it almost doesn't matter.



Since I'm in love with low flow velocities, I use air separators, all the time. Then I don't need to get the air bubble physically back to the mech room. I just starve the water for oxygen and "eat the bubble" over a short period of time. with low, low flow rates



Air scoops work on most systems, but they sure don't offer the same level of guarantee.

Mark Eatherton

Eating bubbles...

I had a manufacturer tell me once that their MBR's were so powerful that they could suck air off the next planet... I think he also mentioned something about some land for sale off the cost of Florida...



I had a "rogue bubble" working its way around my house here in Denver. I tried almost EVERYTHING to get this bubble out, and it HAD an MBR installed. It use to grate on me as I could hear the bubble bouncing along, going from radiator to radiator. I even trapped radiators in an attempt to catch this devil, to no avail. This is a simple one pipe system with venturis on the branches, and Buderi SPR radiators and RF surfaces (walls ceilings, floors) as emitters using non electric TRV's for flow control.



I finally had to resort to the use of dish detergent to capture and expel it, and it was GONE in less than 5 minutes of run time.



Have had numerous commercial jobs that were air binding on the upper floors WITH good MBR's in place, so you can believe their propaganda if you want, but my field experience in more than one situation tells me that they are selling a theory that hasn't been proven.



The key to an air free system is getting the majority of the free air out when it is first filled. If the system isn't conducive to being power purged, that is a design issue. In systems where purge velocity cannot be obtained, one has to do a bottom fill, top manual purge to get the air out. Short of having a fire truck for a purge cart, you can't obtain adequate velocity on 3" pipes to push the air around.



Hydronic systems have been around for a lot longer than MBR's, and when done right, have been virtually air free and silent since forever.



MBR's were initially introduced for a perceived "problem". That problem being, system that became air bound. Those systems with recurring "air problems" had their pumps on the return, pumping towards the PONPC. When the pump is pumping away from the PONPC and air elimination system, the problems are non existent, regardless of the air removal device.



When we tested the scoop's versus the MBR's for the Goodyear trials, we found that they BOTH lowered the oxygen content to the same level, although to their credit, the MBR's did it quicker. Interestingly, when the pumps were shut off, the O2 content ended up coming back to saturation point within 24 hours, but didn't cause any inadvertent air binding in the systems, which were intentionally designed to cause trapping of air in the upper regions. Remember, we were testing Entran 2, which passed oxygen like a sieve.



To each his own, just saying what my experiences are.



ME

NRT_Rob

sure thing

I appreciate you sharing your experience mark. It's certainly worth thinking about.

Brad White

Air rises when immersed in water...

I do not think that anyone who is sane will argue that a MBR will remove all air from a system, especially the upper reaches, but it will remove nearly all air from water passing through it.



Once a good slug of air is trapped at the high reaches, venting and purging, plus a dose of Dawn detergent (thank you Mark, our dishes are now also sparkling clean!(tm) , you can have success, peace and quiet.



The notion of 4 FPS to remove air and carry it down a few stories might apply to small-tube systems but means nothing in old gravity HW piping. Radiator key vents are your friends.

BEXX

sizing chart

On a somewhat related part of this conversation , where can a person find a pipe sizing chart for the main pipes that run to all the cast iron radiators? I see a link on the Heating Help webiste but there is no information behind the link?  Is there a chart that will determine how many btu's a 1' pipe will carry at a certain GPM and the different water temperatures?

Scott

Brad White

Existing Old Piping or New?

"It depends". Burnham and others have handy guides which have tapping sizes used for hot water and steam, such and such a size for so many square feet EDR.  When the old gravity systems are used with circulators, the pressure drop is almost impossible to register without very sensitive gauges, even the digital ones.



For example, in my own house (about 2,200 SF, American 4-square, built in 1913), I have a 3" original boiler connection branching into a pair of 2-1/2" pipes running equally in both directions. The radiators will require 3.5 gpm at a 20 degree drop. OK, call if 4.0 gpm to make an even number. Running 2.0 gpm in a 2-1/2" pipe will impose a pressure drop of..... ready? 0.0064 feet for every 100 feet of pipe. Yawn.



This is why I like continuous circulation with gently varied temperature.



Here is a chart I use, more conservative than most, but you can debate how much more flow you can impose: BTUH ratings presume a 20 degree drop. Go to 40F and double the BTUH rate.



1/2"- 1.0 gpm, 10,000 BTUH



3/4"- 3.0 gpm  30,000 BTUH



1"- 5.0 gpm  50,000 BTUH



1-1/4"- 9.0 gpm  90,000 BTUH



1-1/2"- 18.0 gpm  180,000 BTUH



Slight differences iron to copper, not enough to be concerned about.

Ironman

Very Informative

Mark,

I appreciate the good input on scoops vs. MBRs and have no disagreement with your points. I prefer the MBR for 3 basic reasons, maybe 4:

First, the MBR does seem to work much faster on initial purge.

Second, it does not require the 18" minimum spacing between it and an upstream ell.

Third, most manufacturers spec. or recommend them with their mod/cons.

Fourth, the the auto vents on top of the scoops are notorious leakers and leave a nasty looking rust stain on the scoop when they leak. I haven't had any problems with the MBRs leaking so far (8 plus years now). And being brass, a stain would not be as bad. They are also now being offered for vertical pipes.

Mark Eatherton

All valid reasons...

BTW, the rumor about needing 18" fore and aft is based on constant flow at maximum rated velocity. That rarely happens in the real world.



None the less, points well taken, Just didn't want to see the baby thrown out with the water. :-)



Thanks for responding.



ME

Ironman

KEK BOILER FLUSH

Brad,

Just curious if you're familiar with this product? All natural stuff. The manufacturer says you can leave it in the system. Haven't used it yet, but just ordered some to flush a 100 year old gravity flow system where we're going to install a mod/con. Made by Kenite Labs. Meshopen, PA. Roy Hall said it works great.

Brad White

KEK

Hey IM! I have heard the name, but could not place it, so am not familiar with KEK as a cleaning product.



But leave it IN the system? Mmmmm. If strong enough for a man... oh wait, strong enough to clean the pipes, does it know when to stop?



But I will look into it- Thanks!



Brad

Plumdog_2

Another Scoop Man

Even though the most popular MBR is brass, I have seen (on several occasions), the little wire basket inside rust apart and the wire pieces go sailing into the pump. And I have had them clogg up and stop flow. And how do you clear the air vent without taking the darn thing apart? Proper piping will negate the need for it, and save headaches down the road.

Mark Eatherton

I guess we're hydronic dinosaurs Plumdog...

Cost effective dinosaurs :-)



I suppose that 80 bucks is no big deal in the grand scheme of things.



I'm with you. Servicing them is a pain. Caleffi does have a better design with service in mind...



There's a million ways to skin a cat, and eliminate air...



ME

tim smith

RE: air seps, etc etc

Mark and all, I totally agree with ME on this. The most important thing is to get the piping right the first time and air won't be a problem. Most all of our jobs are old iron conversions and rarely do I see a benefit to an air scrubber. Still my favorite type of installs are from the early 1900s that are old overhead gravity systems. When we convert over to forced hot water, low flow. They are such a dream to get the air out of. Install a purge valve on top of system and let her rip when we fill, don't have to bleed each radiator, air just flushes to top. Pretty cool. Tim

Jean-David Beyer

little wire basket inside rust apart

The Taco 4900 air eliminators use stainless steel "pawl rings" instead of fine wires. But the principle of air removal is the same: present a large area with low flow rate on which the microbubbles can deposit themselves. When enough of them coalesce, they float off to the top of the unit where a valve lets the air escape.