Difficult high efficiency residential boiler selection

JohnNY · July 24

Hello all,

For the second time this year I'm trying to select a boiler against a handful of challenging and limiting criteria made especially difficult by the fact that Weil-McLain calls a 4" polypropylene 90° sweep the equivalent of 22' of straight pipe, Lochinvar Knight (floor mount) rates the same fitting as 10' of pipe, and Peerless assigns it 5'.
It's a 6-story home so I've got about 72' from boiler to roof line, and my static water fill pressure will be around 35 PSI at 70°.
I'm burning roughly 300 MBH for space heating and an 80-gallon indirect.

I guess my biggest issue is the wide range of equivalent pipe lengths per same fitting on the flue. I would really like to install a WM Evergreen but my flue would be over extended due to the total developed length of my venting materials.

The math above all points to the Peerless Purefire as the boiler for this project but there are some features it doesn't seem to have such as the ability to limit my maximum fan speed while in central heating (CH) mode. I find that useful in many applications. Both Lochinvar and WM allow this flexibility. Also, Peerless does not seem to offer a pre-fabricated manifold kit like the others do. Adding a heat exchanger would solve some problems for the low pressure tolerance of the Knight boiler and some others but I don't have the space to add one in a clean way.
I'm looking for advice. Is there a boiler out there that runs at about 300 MBH, has a HX tolerance of at least 50 PSI, can vent 100' with three 90° fittings, and is suitable for a residential application with good control parameter options for flexibility?

GGross · July 24

my assumption is this is probably too large for the space

Viessmann CI2 can meet the venting requirements. I do not think you can specifically control the viessmann max fan speed (viessmann likes to control their own burner) but you can limit the max output for heating mode which will also limit the max fan speed for heating mode. unless that was the goal in the first place. these are high mass units not water tube like most viessmann.

I think the boiler comes with an 80psi relief by default so specify your relief size when ordering, you can save some money by providing your own relief valve if it matters. These are light commercial focused so they are designed first for room air dependent combustion air, if you are direct venting with 2 pipes there is a combustion air inlet kit you should ask for. they will also provide a filter for the burner for room air operation if you want (it's like a high performance auto filter)

Jamie Hall · July 24

I think the Weil-McClain equivalent length for the 90 is very conservative. However, all is not lost. There are two directions I would approach this one from. Consider that what they are interested in is not tape measures, but pressure drop in the ductwork. WM want to make sure that that pressure drop is not excessive, and I can't say I blame them for that.

So, instead of getting out the tape measure, actually see what pressure drop they can tolerate, and then find a qualified engineer (which I'm not, sorry — never was my field) to design an exhaust which meets that specification. I'm going to go out on a limb (scary) and say that either a larger diameter exhaust with the same geometry would to it, or even the use of long sweep elbows might be enough. (scribbles on the back of the envvelope… if they rate a 4 inch at 22 feet, a 6 inch should rate at just under 6 feet… but don't quote me on that).

JohnNY · July 24

@GGross Great answer. Interesting boiler.
Thank you.

GGross · July 24

here are some photos one of my customers sent me from a service visit. he buys those K&N filters from the auto store for all of his mod/cons. the HXC sort of looks like a water tube when you see how he cleans it but its not. its made of a bunch of stainless steel sheets with a criss-cross pattern pressed together

EBEBRATT-Ed · July 24

@JohnNY

I suppose you have to follow the boiler venting requirements, but I do wonder what the polypropylene mfgs say about fitting resistance. Any difference between MFGs?

Can't vent sidewall I assume?

GGross · July 24

https://forum.heatinghelp.com/discussion/comment/1900787#Comment_1900787

Not sure code in his region but in mine the inspectors will look at both (equipment, and material manufacturers) and apply the most stringent of the two

Kaos · July 24

@GGross I hear those K&N filters can improve the 1/4 mile time, though it is really hard to measure accurately for a boiler.

EBEBRATT-Ed · July 25

Duravent says a 45 ell =5' of pipe and a 90 ell=12' of pipe that is in 4"

Centrotherm has 15, 30,45 and 87 degree elbows

Centrotherm also has flex polypro, don't know if that can be used. Didn't see any elbow equivalents on their site.

mattmia2 · July 25

offsets with 45's or even 15's or 30's can make the equivalent length a lot less than 90's if you can do it.

JohnNY · July 25

EBEBRATT-Ed · July 26

Don't know if I am reading this right the Weil McLain is confusing

For 4" PVC they deduct 7' of 4" pipe?

For Centrotherm they deduct 20' for one elbow

For Duravent 22' for one elbow.

For the Peerless 1 elbow =4' for long radius and 5' for short radius"

All 4" pipe.

Jamie Hall · July 26

You are reading it right. I'd have to look — very closely — at the various fittings and joints to find out why… something about radii and geometries.

hot_rod · July 26

if you exceed the distance allowed by a few feet, what happens?

I’ve heard it basically derates the burner. Same with choking the intake. Or when an intake is partially blocked with bugs.

Or would it cause lockouts?

Good questions for the burner engineers. I suspect there are some running beyond suggested distances.

EBEBRATT-Ed · July 26

But why the 7' deduct for PVC and a 20 or 22' deduct for polypropylene on the Weil McLain?

And Weil wants a 100 foot run max while Peerless lets you go 200'

Same firing rate and the Co2/)2 would be about the same so the same volume of flue gas.

Seems a bit out of wack to me.

mattmia2 · July 26

https://forum.heatinghelp.com/discussion/comment/1900880#Comment_1900880

most of those pages like like some engineer wrote that page in 1994 and has long since retired and they are just printing the same page they've been printing for 30 years and the person that understood it is long gone.

Danny Scully · July 26

@JohnNY , you could use the Evergreen if you switch to PVC. Is that a no go?

JohnNY · July 26

https://forum.heatinghelp.com/discussion/comment/1900884#Comment_1900884

Unfortunately, PVC is not allowed for venting in NYC.

Mad Dog_2 · July 26

It's not allowed in the rest of NYS either, only for Air intake. Mad Dog

JohnNY · July 26

https://forum.heatinghelp.com/discussion/comment/1900879#Comment_1900879

@hot_rod You are right. The efficiency drops when the flue is extended and makes their published ratings inaccurate. But the boiler will run.

JohnNY · July 26

Is that right, Matt? Not Westchester?

JohnNY · July 26

https://forum.heatinghelp.com/discussion/comment/1900880#Comment_1900880

Yeah it’s crazy to me too. Notice the Peerless ratings refer to a combined length for both the air intake and exhaust. If I could take the air from street level and exhaust to the roof it would make a difference but I don’t have that option now and both will run about 70’ to the roof terminal points.

Tom_133 · July 26

The NTI TFTN is a 285k or a 340K, and both can go 150'. Not sure if that helps you since I didnt read every post.

I like these boilers, and the controls include a lot of options

EBEBRATT-Ed · July 26

Venting in MA must be polypropylene in most cases now as well. PVC is questionable (IPEX makes pvc vent pipe) if the MFG allows it I think. PVC ok for intake air.

If an existing installation is vented with PVC and it is buried in a wall and you replace the equipment, they will usually let you attach to the existing PVC if it is still in good condition and has not been overheated and the replacement boiler or furnace allows PVC.

Very confusing in MA. They are trying not to make it a hardship but want it safe.

Mad Dog_2 · July 26

All of NYS, but of course, we still see it, some slip by. When we were getting Factory-Trained at Buderus in NH in the Early 2000s, on the Buderus GB Mod Cons, I asked that same question on the vent distance and they assured us they would still work fine and safely, but that combustion efficiency would suffer a bit. After they were out about 2 years, the code was amended and all the Mod Con manufacturers wrote it in to their manuals. First it was "no foam-core or Cellcore PVC, and then standard Schedule 40 PVC was out too. Mad Dog

Danny Scully · July 26

Where are you seeing that @Mad Dog_2? NYS fuel/gas code seems to reference its allowance if manufacturer approved/listed.

EBEBRATT-Ed · July 26

AFAIK

IPEX manufactures the only PVC & CPVC I know of that is listed for flue gas venting and it says so right on the pipe. See the attached.

brochure-usen-ipex-system1738.pdf

Danny Scully · July 26

Charolette puts the responsibility on the boiler manufacturers. I’ve routinely seen schedule 40 listed on many condensing boilers.

JohnNY · July 27

https://forum.heatinghelp.com/discussion/comment/1900897#Comment_1900897

This does help. Thank you. Actually, this boiler is something close to perfect for this installation. I know NTI has rabid fans who swear by them. I'm surprised they're not doing a better job of marketing themselves.

Mad Dog_2 · July 27

https://forum.heatinghelp.com/discussion/comment/1900901#Comment_1900901

IFGC 2024 (International Fuel Gas Code) 503.4.1 as well as RCNYS 2025 (Residential Code of New York State) G2427.4.1 both state: "Plastic piping. Where plastic piping is used to vent an appliance, the appliance shall be listed for use with such venting materials and the appliance manufacturer's installation instructions shall identify the specific plastic piping material. The plastic pipe venting materials shall be labeled in accordance with the product standards specified by the appliance manufacturer OR shall be listed and labeled in accordance with UL 1738"

Without naming names, most boiler and water heater manufacturers cover all bases and regions and actually do state in their specs, that they allow Schedule 40 DWV PVC Pipe and fittings (Only rated to handle 140 F) for flue gas venting, even though is not UL 1738 Listed or rated. With code disputes and interpretations, the more stringent standard is used. The only manufacturer that I am aware of that makes UL 1738 PVC is IPEX. I,too, still see it done out there, but that doesn't always mean they had it inspected or that some inspectors may not catch it. We haven't used Schedule 40 PVC for flue gas venting in more than 20 years. It's CPVC, PP (polypropylene) or Stainless Steel. Why take that chance? Especially with Flue product. Mad Dog

EBEBRATT-Ed · July 27

@Mad Dog_2

Agree the IPEX CPVC is rated in the 170s I think.

GGross · July 27

https://forum.heatinghelp.com/discussion/comment/1900918#Comment_1900918

I think they are bouncing back a little. pretty sure emerson swan reps them through their territories if you are familiar with them. they might have some direct manufacturer representation in NYC though not sure.

JohnNY · July 27

@GGross They are repped by Wales-Darby in my area who are generally excellent. However, I called their office today and was told that Ferguson was a stocking distributor. I spoke to someone there and they clearly are not. I made a few more calls and found an HVAC supplier who has the NTI I'm looking for on the shelf but wouldn't sell to me or even give me a price because I'm not "in their system."
So, I tried and failed to purchase what was probably the best boiler for the job today.

I've used the Peerless Purefire before and with perfectly good results so I'm not very disappointed but it was a waste of two good hours this morning trying to act upon a good recommendation.

Also, the whole HVAC industry, all of it, can bite me. It's the only sector of the building trades where collusion and price fixing are accepted as normal business practice.

Mad Dog_2 · July 27

Incredibly frustrating…Mad Dog

EBEBRATT-Ed · July 28

Doesn't FW Webb sell them?

I checked the NTI site and there are 27 distributors in NY, NY. Some are listed double as they have branches.

What kind of a rep is Wales Darby if they don't know what distributor sells their boiler?

Isn't that kind of like what they do all day every day?

mattmia2 · July 28

https://forum.heatinghelp.com/discussion/comment/1900991#Comment_1900991

this sounds like seinfeld at the rental car counter

Tom_133 · July 28

Thats a bummer. In some ways I was hoping Supplyhouse.com would pick the line up, because they stock so much! On the other hand it's nice not to get berated by a new customer who is questioning my mild mark up because they saw the price of the boiler online. Recently I was thinking of switching everything to Lochinvar but Webbs is the only wholesaler in my area carrying them. Where as NTI is sold by Granite Group, Blodgett Supply, Hulbert Supply, so typically I can get what I need for parts quickly. If Lochinvar had a maintenance kit for a guy who installs only 30 boilers a year I would take the leap.

hot_rod · July 28

https://forum.heatinghelp.com/discussion/comment/1901003#Comment_1901003

https://assets.lochinvar.com/damroot/Original/10017/Parts%20kit.pdf

Difficult high efficiency residential boiler selection

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