Plate exchanger VS Tankless Coil

So I've been looking into these two options for my AA when it's finally put back together. I'm struggling to land, maybe some of you can share your experience/insight? From what I've gathered- ( and I could be all wrong on some of these!)

Plate
Pros: External, easy switchout, size selection broad, more heat per boiler volume since it circulates the water

Cons: Lifespan shorter, slight pressure reduction, buildup, constant circulation, slightly more expensive (?)

Coil
Pros: Longer life, can supply hot water without power (on a city system), slightly cheaper
Cons: Internal (requiring boiler shutdown for replacement), limited to boiler cavity size

What do you all think? I'm not real crazy about a plate exchanger that would have to be replaced <10 years. I'm also not crazy about the constant circulation concept. I'm leaning towards the coil, let me ask this too, has anyone done BTU transfer comparison between 'finned copper coil tubing' and just standard copper tubing? I know it's all about surface area-but I'd be curious to know the difference.

Any other suggestions?

In your "Cons" for the plate exchanger, why did you list Lifespan shorter, slight pressure reduction, buildup, slightly more expensive? I don't think any of those are true.

And, there are ways to get around the "constant circulation" if you need to.

I don't think you'll find a DHW coil for any boiler much under $300. The plate exchanger I use was about $150 and it is twice as big as what I really need.

-Don

StokerDon wrote: ↑

Tue. Mar. 22, 2022 8:01 pm

In your "Cons" for the plate exchanger, why did you list Lifespan shorter, slight pressure reduction, buildup, slightly more expensive? I don't think any of those are true.

And, there are ways to get around the "constant circulation" if you need to.

I don't think you'll find a DHW coil for any boiler much under $300. The plate exchanger I use was about $150 and it is twice as big as what I really need.

-Don

This is why I'm asking, I found some scattered articles/videos but not much substantial, the one video I watched was for outdoor wood boilers and the guy said this plate exchanger was heavy duty and would last more than 10 years....that didn't sound so positive...a domestic coil from AA is $240. My parents are on city water and I don't think the coil has been replaced since '97 when we moved there. I've heard similar numbers from people with tankless coils.

This stuff is all super duper super super super massively super new to me so I will sound rather stupid with some statements and q's.

There is a 3rd option not on your list. The indirect water heater aka Boilermate types.

But whichever you use plumb it correctly. There are particular dos and don’ts any most will mess it up for lack of knowing what needs to be done.
Don’t count on YouTube gurus to be the authority on the finer details to proper plumbing of domestic hydronic heated HW.

I think you captured the pros and cons pretty well. I think if your water is hard enough to cause buildup in a plate hx, you would also have buildup in the tankless coil. With either you should use a water softener if needed, and pipe to allow flushing/service.

In the case of a remote boiler, a plate hx and indirect water heater allow you to have DHW where you need it, rather than having an extra run of long piping to a remote tankless coil. A side-arm on an existing water heater is another option.

I use a plate exchanger on my Outdoor Boiler. In service for 12 years so far without any appreciable loss of efficiency. My boiler water is treated though.

Thanks Gentlemen, does anyone care to expound on the possibility of a plate exchanger without a circulator? To me it sounds like maybe this setup would require a separate storage tank to take advantage of what's it called, thermosiphon (?). I assume this is a slow process and is to bring a tank up to temp and then hot water is drawn from the tank, not directly thru the plate. But that's just how my imagination works, I can't seem to conger up a mental picture of hot water circulating thru that little plate fast enough to heat the tap other than being pushed with a pump. If anyone has any book resources on the topic, I'd be interested.

McGiever wrote: ↑

Tue. Mar. 22, 2022 8:19 pm

Don’t count on YouTube gurus to be the authority on the finer details to proper plumbing of domestic hydronic heated HW.

I don't think there's anything on YouTube that I would consider a 'proper authority' haha, but thanks for the caution. Knowing enough to be dangerous is classic pitfall of DIY's like myself.

Retro_Origin wrote: ↑

Wed. Mar. 23, 2022 6:21 pm

I can't seem to conger up a mental picture of hot water circulating thru that little plate fast enough to heat the tap other than being pushed with a pump.

The domestic water is already being pushed by pressure via your well pump or city water pressure so that part is already covered.. As far as the boiler water is concerned, in my mind yes, there does need to be something driving it, natural circulation isn't gonna do it.

I suppose if your looking for a natural circulation situation, you would use a side arm exchanger on your existing tank. But unless there is some very clever plumbing involved, something will still need to drive the boiler water thru it. It is possible though. You'd have to keep the supply pipe high and the return pipe low, which would probably be a trip hazard unless you mount the hot water tank right beside the boiler lol with exclusive piping to and from the boiler vessel.

Having your boiler remote in your chicken coop sure makes the options for DHW setup tricky.

Mine is setup on my garage loop so it goes to the hot water heater (where plate exchanger is) first on it's way to the garage modine. Not sure if you could incorporate into an existing loop but this method works very well. I originally started with an outdoor wood boiler and that was setup the following: from boiler to side arm heat exchanger on water heater then to house furnace coil, all one loop.

McGiever wrote: ↑

Wed. Mar. 23, 2022 9:55 pm

Having your boiler remote in your chicken coop sure makes the options for DHW setup tricky.

Yeah, I should clarify, I will be moving this into the basement eventually, right now it will not have DHW..but my decision will determine whether I weld the plate to the boiler or just use a gasket for now.

swyman wrote: ↑

Thu. Mar. 24, 2022 7:58 am

Mine is setup on my garage loop so it goes to the hot water heater (where plate exchanger is) first on it's way to the garage modine. Not sure if you could incorporate into an existing loop but this method works very well. I originally started with an outdoor wood boiler and that was setup the following: from boiler to side arm heat exchanger on water heater then to house furnace coil, all one loop.

Does this mean you only get domestic from your 260 during heating season? I suppose if you're remote anyway then it DOES make a lot of sense to use the plate since you have to circulate anyhow.

Lightning wrote: ↑

Wed. Mar. 23, 2022 7:15 pm

I suppose if your looking for a natural circulation situation, you would use a side arm exchanger on your existing tank. But unless there is some very clever plumbing involved, something will still need to drive the boiler water thru it. It is possible though. You'd have to keep the supply pipe high and the return pipe low, which would probably be a trip hazard unless you mount the hot water tank right beside the boiler lol with exclusive piping to and from the boiler vessel.

Given the small size of the axeman I think I might find this challenging. I need to research some more. Given my odd preferences it looks like I might be going the coil route!

Retro_Origin wrote: ↑

Thu. Mar. 24, 2022 5:26 pm

Does this mean you only get domestic from your 260 during heating season? I suppose if you're remote anyway then it DOES make a lot of sense to use the plate since you have to circulate anyhow.

I used to be remote but moved my boiler in the basement a couple years ago. My plate exchanger is mounted on the cold supply on my water heater and it thermosyphons (not sure if right term) and heats all the water in the tank. It is an electric water heater and I shut the breaker off while the boiler is running through the season and simply turn the breaker on when I shut the boiler down. Works out great.