Newer Boiler on Mouat Vapor System

Unfortunately the installer did not pipe it right. Don't know why they can't read the manual.

You have the two boiler supplies opposing each other with the building supplies in between. Since the header is large it may or may not work ok.

No Hartford loop but it may not be needed if that boiler feed tank is in use. Is that tank in use?

What is the 3/4" copper coming off the top of the tank? That doesn't look right. There may be other issues not seen.

IS YOUR FLUE PIPING HEADING DOWN INTO THE CHIMNEY???

I have a 100 year old Mouat System too. System is all original except boiler is 1957. Also have a 4 inch header but I my boiler is 2 times the size of your new one and has 4 inch connections so it was tied straight in to the original piping. So I am wondering what the size of your system is.

A Mouat system is designed to run at ultra low pressures. I've never seen more than 3 ounces pressure at the header. I consider my vaporstat to be a safety device only.

For a quick size idea if you haven't calculated the EDR how many radiators are in this system? I have 23 total on 2 floors.

The venting on this is too small. Get a Gorton #2 to replace each of the existing vents.

Hopefully @gerry gill will see this.

I built a custom control many years ago when I realized that these systems were never designed to be full of steam. Pressure can only build when radiators are starting to get full. These systems were designed with a lot of extra radiation so heating the space does not require filling the radiators at any time. More even heat requires radiators to be only partially full a higher percent of the total time. The standard pressure based control where call time equals burn time has no chance to provide this. That control, which will allow radiators to fill enough to make pressure, is making uneven heat, or at least far less even than it could be. So I even out the burn time required to heat the place in shorter evenly spaced burns and the system never gets close to full so there never is any pressure. I don't have or need any vents on the mains either. Burns are always 2 per hour maximum +/-.

it is really hard to tell in that system what is connected and what is abandoned.

@dcw1 , Tell your son he has a great system there, and a museum piece.

I do have one vent but is it not on a steam main. It is on the dry return far away from the boiler. I need very little venting because I don't let the air back in once it is pushed out.

Mouat systems were high end and installed in larger homes in NE Ohio. My house is 3500sqft. I have a big boiler that barely burns 50% of the time to heat at -20F. I still can run it with no pressure ever and I don't think size means much as long as long as the boiler is big enough. Actually I think all the advantage goes to the bigger boiler with the right control.

So I expect your new one is big enough. Give us the radiator count and EDR figure. Does it heat everything Ok?

Looking at the Mouat sales literature it looks like that old boiler is in fact the original to the system. Quite a rare prize to have. I've attached the literature here if you don't have it.

Some general comments, as this provides an opportunity to point out some things:

The original design had installed significant extra radiation beyond what was actually needed on purpose. It had lots of extra boiler too. That big old boiler you have still has the low pressure control on top which modulated the damper on the coal fire matching the steam production to the current demand in real time. The boiler never ran on "high" or "off" and the radiation was never close to full. Nothing about the size of the boiler was "critical". The steam production was continuously varying with the demand, all at ultra low ounces of pressure.

What is important to note about the original design:

1. Lots of extra installed radiation continuously partly filled never full.
2. A big boiler intended to run in the middle of its range - there was no "high" speed and no "off" speed
3. 3 ounces of pressure maximum was all that was required to deliver the steam in all states of demand(so why today do we need pressuretrols and vaporstats for this system????)
4. The control system reacted in real time to demand changes by sensing very small changes the header pressure

Now contrast that with the standard control they came up with to run the intermittent on/off boiler that replaced the original. That control can ONLY run the boiler on high or be off. That control runs the boiler on high until either the tstat is satisfied or the system fills enough with steam and a pressure well over 3 ounces is detected because radiation that never was needed or intended to fill is now full or close to it. That is an extremely poor substitute for the original except, well, it did solve the coal and smoke problem. This "solution" somehow also launched a quest for the mystical "perfectly matched" boiler size since modulation went away, as if one magical single speed boiler size could possibly replace modulation - wait what? Perfectly matched to what? An amount of radiation never needed or intended to be used? What amount then? And what, the "perfect" boiler size will satisfy the tstat on one continuous burn without the pressure reaching the lowest cut out setting you can put on a vaporstat meaning call time equals burn time? That is the goal? That will not produce heat close to as even as these systems are capable of. Long calls are what prove that heat is even because the temperature is rising from cut in to cut out very slowly. Long calls are what happen when actual net boiler output is closely matched to current demand. That is the only thing that really needs matching to achieve even heating, and that has much more to do with how long and when burns are than it does with the capacity on the boiler nameplate. Perfectly even heat would be a call that never ends right? So if the heat is really even the burn time must be much less than the call time if all you have is a one speed(high only) boiler. They can't be the same or even close to the same. That can't be the result (and surely not the goal) if the project is even heat.Currently my system is showing calling for heat 67% of the time and burning 29% of the time. The weather is mild in the 20's.

I knew nothing of steam when I bought the house 33 years ago. But as I observed this on/off big boiler vaporstat controlled air breathing in and out system run, as an engineer it just seemed crazy. Radiators went from boiling hot down to room temperature back and forth over and over with long waits in between. Air was pushed out of basement vents only to be sucked immediately back in. It was quite apparent that a control with only those two inputs - tstat and a pressure device - had no chance of providing even heat anything like what the original control system must have. So I set about changing things. What was abundantly clear early on was that the control needed to react to the demand in real time somehow, like the original did, for decent results. That and that some form of output modulation was in fact needed, as the dead men obviously knew, so that high speed burns would be divided in pieces shorter in duration and spread out evenly. Its called PWM Pulse Width Modulation. There are many ways to do these things and it really isn't that complicated. Unfortunately no contractor will help with it.

So what did I do? I added a remote temperature sensor to run every burn to the same partial fill amount no matter the starting point cold or not. I stopped letting the air back in and used the natural vacuum to both balance the heat and to provide feedback about the current demand, based on how fast and how much vacuum forms. Subsequent burns start when the remote temp sensor opens again indicating it is time for more steam if a call is still in progress. There isn't a sound now, radiators are just roughly the same warm always unless it is extremely mild out, and no one is aware anything is even happening. Burn times and waits in between are always changing with the conditions. The system always settles in at 2 burns per hour +/- if there is any real demand. Venting ceased to be a consideration. The difference from what I moved into is dramatic.

i'd throw a couple unions in there so you don't have to disconnect stuff to take it apart.

you can also make the water seal out of tees and ells and plugs such that you can flush it out by just removing the plugs.