Portage and Main and general questions

Apologize in advance as this post might be a little long and boring. I figured I might throw in the whole story, rather than asking questions here and there; the bigger picture is always better after all.


I’m currently looking to change my whole heating system (from electrical space heaters with an awkwardly placed free standing wood stove) to either a hydronic furnace powered by a gasifier (which means I would need to retrofit ductwork in the house), or radiant flooring for the first floor with hydronic radiators in the basement and second floor. I’m in the process of making a detailed heat load calculation of my 1,600 square feet 2-story home. This portion of the design has yet to be discussed with the local installer as to what would be less costly and more appropriate for my house.


Although I have not separated the electricity consumed for things other than heating, I have the data for a -25 day (which is still -7 degrees short from design temperature), it appears that I used up 215.7822 kWh, or roughly 350,000 BTU on a 24 hour period.


Regarding the gasifier, the only local dealer in my community carries Portage & Main boilers. Although I am not too fond about an outdoor wood boiler, I am considering making a 20*10 heated outbuilding with the Economizer IDM 100 (there only indoors gasifier, with a maximum rated output ranging from 90,000 BTU to 140,000 BTU – depending on what web site you are looking at) with enough space to install 2-3 thermal tanks of 400 gallons each (questions regarding this approach follows).



My first issue: according to P&M’s FAQs :


“Our gasifiers and boilers are specifically designed not to require additional water. Therefore, there is no need to have an additional storage tank. With the exception of commercial applications such as greenhouses where most of the heat is required at night, having a large storage tank of 2000 to 10000 gallons is not necessary.”


From what I have read on here, -ANY- gasification boiler can benefit from additional storage as it creates a known demand, reduces idle time, burns cleaner, etc. I have sent an email to P&M regarding this issue, but I have not received an official answer as of yet. Does anyone know why they would advertise such claims? Does there design really have no benefit of adding additional thermal storage for residential applications?


My second issue is in regards to the question that has been dealt a thousand times, but I am still not sure I understand fully… low temperature return / corrosion issues. From an old post made by heaterman :

heaterman said:

The issue with your boiler or any boiler for that matter, is flue gas condensation. It simply has to be prevented in any boiler that is not designed to withstand liquid instead of vapor in the heat exchanger and flues. Doesn't matter if you're firing with wood, coal, oil or gas, Flue gas condensation will without fail eventually wreck your boiler.


So ...the simple solution to preventing said condensation from happening is to keep the flue gas temperature above the dew point or otherwise said, the point at which vapor in the flue gas turns back into liquid. In most scenarios (there are a few variables) you will find that in order to maintain sufficient flue gas temp the water temperature must be kept above 140* for solid fuel appliances. (Moisture content of the fuel is a significant factor in this also)


This is done in a couple of different ways. One being the use of a termovar diverting valve that routes hot water back to the boiler before it hits the system. The other is the installation of an aquastat the turns off the boiler circ should water temp drop below the setpoint and allow the boiler to "catch up".


I had my combustion analyzer in a couple of flues this past week looking at the dew point among other things. The first piece of equipment was a standard downdraft gasser the owner was having issues with from creosote plugging things up. While the design of the boiler is less than stellar and contributed to some of his problem, his main issue was wet wood and a lot of idling. Moisture content of the wood (oak seasoned last summer and this) was still over 28% in many splits. The dew point of the exhaust gas was just under 150* which is very high. This means he has to keep his water temp somewhat above that or the flue gas will be too cool and it will rain in the chimney. This is a very bad thing.In his situation the boiler was connected to a huge load (several thousand sq ft of concrete slab) that dropped the water temp below

the critical point. Lot's of black goo everywhere. He will be installing a pump aquastat to kill the main circ when water temp drops below 160*.


The other boiler was pellet fired and due to the design of the boiler and the extremely dry nature of pellets the dew point of the flue gas was running only 116* to 118* degrees. This boiler has an integral pump aquastat that can be adjusted to different set points. We set it to tuen off the circ at 140* to give him a margin for error/variability.

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If I understand this post correctly, the added thermal storage will reduce if not eliminate the idling time, meaning that one could do burning-batches and let the fire die out without being reignited for prolonged periods (for as long as the heated storage suffices). As long as there is no flue gas in the exhaust, there is no risk of condensation… I’m I correct? The problem with condensation occurs when the fire is idling too low that the gas can’t/isn’t heated enough, correct? Theoretically that would mean that the fire could be out for days and living with the storage without risking condensation?


My third and last question revolves around the pressurized and non pressurized storages. I understand the pros and cons of both, but can someone install a pressurized system on a non pressurized boiler? If I read and understood correctly, it is doable, with a heat/plate exchanger, but it is not the most efficient option as there is some BTUs lost in the transfer plates occurring?


If you are still reading this, I am amazed! Thanks!

maple1 said:

Don't confine your boiler selection to just what is available locally - you will have to live with the unit for (hopefully) a very long time.

On the condensation, it is not just a function of the stage of fire in your boiler, or flue gas in the exhaust. Creosote can condense in the firebox when burning if it is getting steadily cooled on the bottom with water that is lower than 140, even when burning wide open.

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What scares me most is not being able to obtain servicing should any issues arise...

About the condensation, in that case, it would mean that the storage should never be allowed to go under 140, or have some type of bypass that will prevent the colder temperature from circulating within the boiler? (But what happens when you start the fire again if the water is in the danger-zone)?

maple1 said:

How handy are you?

I bought my boiler from over 1000 miles away - no regrets in my case at least. Very good service from even that far away - there have been a couple of mailings/deliveries from there since the original boiler one, and lots of correspondence & advise back & forth when I installed. If I had stuck to locally available I would still be in the dark ages, I think - your situation might be different. But there are a ton of choices out there. I plumbed everything myself - only outside help was wiring my new hot water heater & electric boiler.

Condensation is handled by thermostatic valve that mixes some hot supply water with return from storage to keep it above 140. It can either be a separate valve (search Danfoss) and a common circulator pump, or a valve/pump all in one unit called a Loading Unit (search LK810).

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I can do basic jobs, as long as someone guides me / shows me how to do it. Although my father-in-law is a handyman, I can't trust his judgement for certain aspects, but he will be of great help for some of the installation.

Aside from the DIY installation, what scares me most is warranty on the installation or availability of parts, should anything break. I can't find myself in a situation where the boiler is faulty and can't run when it's -40 outside... Bottom line is my fears might not be justified, and I am still open to the other companies, just leaning towards what's "easier" to get, or that will give me some feeling of security.


I understand the concept of the thermostatic, so I think this will be my final question regarding this issue; in order to prevent any risks of condensation, the storage should never go below the danger zone, which is normally set at 140, correct?

hobbyheater said:

Is the house a total of 1,600 sq ft or 3,200 sq ft? Radiant flooring would be the way to go as much as possible and there are apparently new style baseboard heaters that also require lower water temps to work.

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Actually, the total square feet to be heated is 2,350 , described as follows :


Basement = 675 square feet to be heated with hydronic radiators / baseboards

First floor = 800 square feet to be heated with radiant floors using the joist method

Second floor = 675 square feet to be heated with hydronic radiators

Wood shed / boiler room (doesn’t exist yet) = 200 square feet to be heated with a hydronic radiator


Although I also have an extremely poorly insulated garage and a barn that I would like to heat, these will be plans for another decade as I don’t think I can afford a boiler big enough at the moment (and it is quite pressing that I change the current heating method for health and safety reasons).

hobbyheater said:

The unpressurized IDM will make it awkward to incorporate storage.

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That is good to know.

hobbyheater said:

Have you considered the Garn Jr.? It has the necessary storage incorporated into its design. This company has been around for over 30 years and still stocks parts for its earliest boilers.

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I have considered and read the models/installation/operating/warranty manuals of the most common brands including Eko, Tarm, Econoburn, Garn, P&M, Profab’s Empyre and Biomass. I did seriously consider the Garn models a while back, when I had 0 clue regarding my actual heat load, and so I had not looked into the Garn Jr, thinking that I needed at least the 1500. So thanks for pointing me back to that model :D I will get a quote on it to give me an idea.

JP11 said:

I completely support the idea of 'buying local'


However, a boiler is something that is so specialized, you should NOT buy the brand just because bubba down at the hardware store got one, and signed to be a dealer so he could save a few bucks and buy 3 at once.


As for parts.. I keep a few fuses around. I'm probably a bit overboard with a complete nozzle set sitting next to the boiler.. But after that.. What's the big deal?


Worst case for availability… say I blow a logic board and I need one.


1. I've got backup heat. You will need it to. something. Electric, plain wood stove, propane… whatever.

2. Is there really anything that can't be had from somewhere in the world and sent overnight freight? I bet I could get ANY part for my boiler within 1 or 2 days.. and the importer is a 10 hour drive away. My dealer is a 3 or 4 hour drive. He's always been johnny on the spot when I call. I bet if I was truly down, he'd be just as quick with any part I need.


I wouldn't hesitate to buy a boiler from a guy across the country.

A GOOD dealer at the end of a telephone with a daily UPS pickup… is 100X better than a crappy dealer the next town over.


Go with the boiler that you want.


Read A LOT on here. I'd steer away from an OWB solely from efficiency standpoint. Don't scrimp on install. As the saying goes…. there's always the money to do it right the SECOND time.


JP

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You brought some very valid point and will strongly consider the other brands. Thank you

Armaton said:

If I read correctly, you only have approximately a 15K BTU per hour design load? Seems fairly minimal. Any of the smaller units "should" suffice. No, the storage temp could be 40 degrees, as long as you have an appropriate thermal protection valve/loading unit you will be good. How it works is the thermal valve takes some of the 180 degree water from the boiler, and mixes the cooler water from storage with it down to a minimum of 140 degrees to insure boiler protection, until return water from storage is 140 degrees, then the valve closes completely and all 180 degree water would go to storage, (In theory). If you are building a "Boiler Shed" anyway, you could incorporate a 500 propane tank for storage and go pressurized, as many on this site have done.

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The design load is still to be determined for precision purposes, the numbers I gave were based on a complete day of electricity (including other than heating usage) just to give an idea.

The thing I have a hard time getting my head around is the fact that if the storage temperature has come down to, let's say 40 degrees as you mentioned, the boiler will have been off during the period that the heat is pulled from storage. Isn't there a risk of condensation while the boiler is cooling down after the last batch burn? I'm not sure I'm getting all the steps involved... :

1. Make a roaring fire that heats up the storage temperature to 185.
2. Fire dies and storage is at 185.
3. Water circulates in the boiler even if the boiler is off since the water is still at 185.
4. Storage gets down to 159 and thermal valve kicks in to prevent cooler water from going in the boiler.
5. Boiler gets cold because it is not reignited, but the storage still manages to keep the house warm since the radiant flooring runs at 90 degrees
6. Storage is down to 120, I am back from wherever I was, and I decide to burn another batch of wood (or 2) to bring back the storage temperature to 185

What happens between steps 4 & 5 to the boiler? Is there a risk of condensation at that point? And what about step 6 , when the boiler needs to reheat from a cold state to a hotter state?

As for the pressurized storage in an un-pressurized boiler, I will need to read more on the subject. So thanks for pointing me in that direction!