68 year old Monoflow distribution: Keep or replace?

Fungohitter

My son and his wife own a 68 year old 1.5 story cape in Concord, NH that's been weatherized. The heating system includes a 35 year old standard oil boiler with cast iron radiators and 1" copper main / 1/2" branch monoflo distribution. It's time for at least a boiler replacement. If the masonry chimney is continued to be used it will need a liner.

Given the costs, efficiencies, and adaptability involved, would it be better to start fresh with an entirely new HE system with new distribution, adapt a HE system to the existing monoflo, or settle for a standard efficiency boiler that will require a stainless steel chimney liner?

retiredguy

If that boiler is not leaking why would you want to replace it. I have always said that a hot water boiler will last until it begins to leak and if it can't be fixed for a reasonable amount only then would I consider a replacement. A 68 year old boiler is old but not that old. I have seen those boilers last more than 100 years. Boilers are not cheap so if you are thinking to replace it and pay for it with the fuel cost savings, you will be very old by the time the boiler pays for itself. My 2 cents.

Ctoilman

Leave the monoflow configuration for sure.  It's a better heat distribution method for your home.  
What's wrong with the boiler there now?  

Jamie Hall

I quite agree with the above. First place, leave the monoflo system alone. They work fine just as is. Second, as @Ctoilman said, what's wrong with the boiler that's there now? Even if it hasn't been properly maintained, a competent technician should still be able to clean it and adjust the burner and bring it to within a few percent of a modern conventional boiler.

If the house is wildly over-radiated now with the weatherization, you might be able to squeeze another perhaps 5% efficiency out of a high efficiency boiler -- but only if it is really wildly over-radiated, which seems unlikely. To put that in hard numbers, that translates to maybe $100 per year in oil cost savings. You will be a very old person before you pay off that investment -- even without considering the foregone opportunity cost of the money.

EBEBRATT-Ed

I agree with all the above. If you can find a decent service tech have him go through the boiler, clean, test and combustion check and keep running it

JUGHNE

The house is 68 years old.

The boiler is only 35 years old....right?

I am to do a project that involves removing a non leaking 63 year old gas fired Steam boiler.
Steam units can have a rougher life than hot water.
The steamer does not leak but is twice as big as it needs to be.
Also there are issues with the gas valve/train, zone valves and other accessories etc.

If the weatherization has been successful the oil burner can be down fired by competent people.

Fungohitter

Thanks for all the comments.

JUGHNE said:

The house is 68 years old.
The boiler is only 35 years old....right?

Correct on both ages. Part of the motivation to consider a new system was to bypass extensive work to the chimney, the most necessary being installing a stainless steel liner. Based on all of the feedback, and also finding out what a new HE system would cost, even if the monoflo system could be used with it, putting money into the SS liner appears to be far more cost effective. And the boiler was serviced annually by the previous (and only other) owner, so it's been properly maintained.

Down firing sounds like a possibility to look into. The boiler was sized when the house was almost entirely un-insulated.

With keeping this system intact, i have another question The entire house is on a single zone. 5 radiators first floor and two second floor. Is there a retrofit valve on the market to make output at individual radiators more controllable? These are typical cast iron radiators.

EBEBRATT-Ed

@Fungohitter

You can use thermostatic radiator valve on the rads. You may need apressure bypass valve as well.

@JUGHNE

Who says a steel boiler won't last on steam or hot water for that matter.

I always say the newer boilers don't last because they are fired too hard

Jamie Hall

@EBEBRATT-Ed , would I be wrong to be a little cautious about TRVs on a monoflo system?

Fungohitter

Jamie Hall said:

@EBEBRATT-Ed , would I be wrong to be a little cautious about TRVs on a monoflo system?

I'd be interested in comments re: this concern.

The information everyone has shared has provided a clearer path for decision making on this system. Thank you!

psb75

I agree with Jamie Hall. I wouldn't guarantee the effective operation of a TRV on a monoflo system radiator.
Adding any new resistance to the supply side of the radiator may "mess" with the pressure drop between the "T's."

Fungohitter

psb75 said:

I agree with Jamie Hall. I wouldn't guarantee the effective operation of a TRV on a monoflo system radiator.
Adding any new resistance to the supply side of the radiator may "mess" with the pressure drop between the "T's."

Does that assume that's there already some sort of balance between each T and each radiator? My understanding of standard radiator valves is that they're best left completely open, or completely closed. So in a monoflo system with all valves open, and assuming no difference in resistance in the radiator supplies, and equal sized radiators (which they're not), all rooms are going to receive an equal amount of heated water, and an equal amount of heat.

If all those assumptions are correct, is there any way with a single zone, other than either TRVs to moderate the heat in each room? Are there manually controlled valves that can be opened part way available? But if there are does that result in the same concern expressed about TRVs?

I remember talking to a veteran steam system tech who said balancing steam systems room to room was always challenging because each individual change affected the rest of the system. Is that similar to this situation? Would it work to adjust each TRV or valve until the desired balance of heat is found, and then leave them alone, ie: not changing them on a daily basis?

Jamie Hall

@Fungohitter , your comment that there is some sort of balance between the T's -- and the pipe between them -- and the radiator in monoflo systems is correct. They are a little odd, hydraulically, in that flow is divided between the pipe connecting the diverter T or T's and the radiator, and it divides on the basis of the relative head loss in the two circuits. .

It is not true, however, that if there is a series of radiators taking off them the monoflo main that they will all heat the same, even if they are otherwise identical, since the temperature of the water in the momoflo main will drop after each radiator. Nowhere near as much as in a strict series arrangement, where all the flow goes through the radiators in sequence, but much more than in a parallel fed arrangement.

What I don't know -- and what I'm hoping some one of the folks who really does know, such as @hot_rod or @EBEBRATT-Ed will chime in on, is just how sensitive the flow balance between the bypass and the radiator is to sticking a valve into the radiator feed line -- such as a TRV. My "gut" suspicion is that it could be very significant -- but I'm honestly not sure.

One pipe steam systems can be trying to balance -- though it can always be done -- because, as your veteran steam tech noted a change in one radiator will affect all the others, and not quite the way you expect always. Balancing two pipe steam or parallel piped hot water (that is, hot water systems with individual feed and return mains, whether direct or reverse) is trivially simple -- the individual radiators are controlled by their individual valves with virtually no impact on the rest of the system at all. They lend themselves well to control by local TRVs.

Fungohitter

Jamie Hall said:

@Fungohitter , your comment that there is some sort of balance between the T's -- and the pipe between them -- and the radiator in monoflo systems is correct. They are a little odd, hydraulically, in that flow is divided between the pipe connecting the diverter T or T's and the radiator, and it divides on the basis of the relative head loss in the two circuits.

It is not true, however, that if there is a series of radiators taking off them the monoflo main that they will all heat the same, even if they are otherwise identical, since the temperature of the water in the momoflo main will drop after each radiator. Nowhere near as much as in a strict series arrangement, where all the flow goes through the radiators in sequence, but much more than in a parallel fed arrangement.

Understood, both that equal heat at each radiator would only be in a perfect world, and that a monoflo does help mitigate the imbalance in contrast to a loop with radiators in sequence. What presents an additional issue with this system is the sequence of the rooms served by the T supplies and returns, all off the main loop in the basement. There are four rooms: LR, DR, Kit, Bath and a BR on the first floor in that order, with a thermostat in the small middle hallway. No problem. But there are two 2nd floor bedrooms, one splitting off between the DR and Kit, and another between the 1st fl. BR and LR. So trying to control the heat in the upstairs bedrooms becomes something of an all or nothing choice in each bedroom.

Jamie Hall said:

What I don't know -- and what I'm hoping some one of the folks who really does know, such as @hot_rod or @EBEBRATT-Ed will chime in on, is just how sensitive the flow balance between the bypass and the radiator is to sticking a valve into the radiator feed line -- such as a TRV. My "gut" suspicion is that it could be very significant -- but I'm honestly not sure.

I'll be very interested, too. Thanks again for all the insight.

mattmia2

I don't think that it is true that you can't partially close a valve to modulate the output of an emitter in a monoflow system. It may be tricky and it may be that small changes in valve position can result in great changes in flow or no flow at all, but it isn't like one pipe steam where a partially open valve will fill the radiators with condensate and cause it to not heat at all.

Fungohitter

@Jamie Hall @mattmia2 I've been searching other discussions and other sources, and it appears that with a monoflo, restricting one radiator does result in a significant pressure drop in the main line. The system depends on the flow diverted to each radiator, and the accompanying pressure, for the main to provide adequate flow and pressure to the next branch. So unless I see something back from @hot_rod or @EBEBRATT-Ed to the contrary, we'll be looking for another way to moderate the temperature in those upstairs bedrooms... possibly a separate zone.

clammy

If trv s are added to the existing monoflow system you may find that even when there open needing heat that the flow is less or none due to the higher pressure drop across the valve which is usually a lot higher drop then the original valve . I don’t think I would attempt it if a customer wanted and but a lot depends on the mono flow systems layout and spacing and weather it a first or second floor and the length of the run from the main ie 2 Nd floor . The far easiest way would be to get rid of the mono flow main and switch all the 1/2 drops to pex and run to a good quality manifold w flow indicators then you would be able to add trv to any and all radiators if so desired , this type of system is called a home run and it’s not a new thing I ve ran into then that where done in the 60 w copper . At that point you should have the ecm circulator pump installed that will adjust flow according how many valves are open or closed . On the subject of mod cons verses cast iron I think I would get the chimney lined and install a cast iron put the money saved into a good heat lose to properly size the boiler and install a magnetic separator to protect that ecm pump and a good spriovent micro air elimator and also be sure to install the circulator on the supply pumping away from your air elimator and expansion tank . Pumps on the supply are a standard and really shine on mono flow and home run systems and basically any system as I have described . Aside from a new boiler the best improvements I have done on older monoflow system where re piping and putting the pump on the supply a big game changer usually only had to bleed the furthest 2 Nd floor convector or rad . In the past I ve had customers tell me the gas or oil use was down and that they had never had there heat work so well and that they definitely felt it was due to pump being moved and the proper location of the air elimator and fill . Here s Some real good advice BUY Dan Holahans book pumping away this way if your not doing the work yourself and have to hire some one you will have some knowledge and be able to get the right job done and not not be dis satisfied you can also see if a pro is available in your area Peace and good luck clammy

clammy

You can zone those second floor rads as described in a home run system except leave the mon flow system intact for the first floor remove the tees from the main for those radiators on the second floor and switch there drops to pex and install a small separate pump and manifold for those second floor radiator . I ve seen guys use zone valves and a single pump and it usually always causes issue w the original mono flow when the smaller zone calls unless you install a circuit setter on each zone or just use a seperate pump when dealing w mono flow system and the need to zone parts of it , it really becomes a issue when baseboard is used in conjunction w a mono flow system . Ps when using multi pumps make sureflow checks valve size are installed on the discharge of the pumps or use pumps w flow check built in . Peace and good luck clammy

EBEBRATT-Ed

Since the branches off the mono flow tees are 1/2" lets assume the flow on that 1/2 branch is 1.5 gpm which is worst case senario, i'ts probably less. I would use a 3/4" Honeywell angle TRVs since the baseboard is probably 3/4" anyhow

If you figure the valve Cv and the 1.5 gpm flow the resistance of the valve is equal to about 3-4' of 1/2" copper with 1.5 gpm flowing through it. Not very much

Further the resistance is not additive since only part of the total flow is through the branch.

Fungohitter

@clammy , @EBEBRATT-Ed Thank you both. Two different possibilities to consider. I'd had the thought myself that separating the two 2nd floor BRs and 1/2 Bath from the 1st floor zone (leaving it on the monoflo loop) might make sense. A thermostat in one bedroom, and a TRV in the other might be the answer. These are old upright cast iron rads, so somehow adding an H-valve to combine with the TRV radiator might be necessary. (It also might mean a new radiator in that room.) I'm hesitant to recommend the TRVs on the monoflo at this point simply because it's not my money. That way if it doesn't work the way hoped for, my son's not out the cash without the result. Carpentry, plumbing, and electrical I'll do. Not HVAC Thanks!

dopey27177

If the boiler is wildly oversized you can can lower the aquastat temperature by 5 degrees, this will bring down the heat output of the radiators because less btus will available in the circulating water.
If that is till to hot drop te temp another 5 degrees.

You will not save fuel but will increase your comfort level in the home.

Do not replace the boiler till you have a problem with the boiler.

I worked in homes with HB Smith pork chop boilers that were 75 plus years old, all they needed was a flushing to remove the crud from the system and a little boiler water treatment.

Jake