new tech boiler - Big Old Gravity

PFG

Family plumbing and heating business since1929. I have A Master Plumber's License and 41years in the trade.  Our area is mostly steam and gravity hot water (closed & converted 50+ years ago). With larger and larger tax incentives we have more and more people interested in high efficiency, condensing boilers. I've contacted several manufacturers (Weil McLain & Triangle) to get their take on mixing one of these into a system that literally takes hours to drain in refill...big house a big pipes...tons of water! My only exposure to the "latest and greatest" in technology has been very expensive control replacement nightmares. My latest quote for a old - time customer was originally based on installing a Weil McLain PFG-7. She wants me to go high-efficiency. Someone convince me....PLEASE.

tim smith

Converting old gravity systems

We have done many of these, works great. We use TT Prestige boilers, does not take much pump to do these, really just have to provide enough head to cover boiler as there is no pressure drop in the old gravity systems at the flow rates needed. Drain and flush well,  put large return Y strainer or basket strainer on. You will not be sorry, we just love this set up and have provided lots of savings for these old large houses, apt bldgs etc etc.  Good luck, have fun.  Tim

Al Letellier_21

gravity systems

Likewise have done many of these conversions here in Maine. Primary/secondary set up for boiler(s), constant circulation for system pump (keeps those big old rads warm) and outdoor reset combined with a good WM or other boiler and a TEKMAR control and its a slick and easy system to install, operate and service.

Don't be afraid of it, you're a lot smarter that all that pipe and cast iron !!!

Good luck.

gerry gill

Yes, as the others have said, it works fine.

I like the Triangle Tube best also..although i've had to replace parts on every mod con in the warranty period regardless of brand..very annoying..on the TT it was a gas valve that only went a year..i'm still waiting for my replacement (3 months)..I think i'm going to use a Burnham ES2 next time..but all in all, it works fine..i would only add that i got bit in the butt once because i sized a gravity system to the 'heat loss' of the house..and i don't guess, i measured and used a computer program..the boiler did in fact maintain temperature..but it couldn't deal with a 'set back program' well..and this customer was hell bent on set back..they said it took four hours to recover from the nightly set back..i put computer data loggers in every room of the house, (11) and sure enough they were right..so on gravity systems that have huge quantities of water, i now add some extra boiler above and beyond the 'heat loss required' size to ensure a rapid climb out of setback..hope that helps..

heatboy

K.I.S.S.

The Viessmann Vitola (gas or oil) thrives in the kinds of applications.  Not exactly "new tech", but simple, works very well and virtually bulletproof.  Just simply pipe it in and your done.  No P/S, by-pass or boiler protection needed.  Add a two stage thermostat and you have indoor reset.  Except for a few fuel efficiency percentages, this is hard to beat, IMO.

tim smith

Gerry Gill, some ideas on curing the set back

Use a stat with intelligent recovery for one and also you can use the timed heat up ( I think they call it the offset)  on the TT prestige where if it does not get up to temp in say 20 min or so, I think thats adjustable, it will raise boiler temp 15 degrees every 20 minutes until satisfied. With those 2 items you won't have a problem. The intelligent recovery will deal with the real cold times and just start boiler much earlier.

tim smith

Gerry Gill, some ideas on curing the set back

Use a stat with intelligent recovery for one and also you can use the timed heat up ( I think they call it the offset)  on the TT prestige where if it does not get up to temp in say 20 min or so, I think thats adjustable, it will raise boiler temp 15 degrees every 20 minutes until satisfied. With those 2 items you won't have a problem. The intelligent recovery will deal with the real cold times and just start boiler much earlier.

Jean-David Beyer

I do not have a big old gravity system...

... but I do have a big old concrete slab with copper tubing in it. Thermostatic mass is thermostatic mass. You do it with all that water; I do it with all that concrete. I also have a fancy Honeywell thermostat with fancy setback capabilities. I frustrated myself for years until I read on this site that there is little point to using setback in a situation like mine. Since my new mod|con has outdoor reset, and easily programmed reset curves, a curve for each of my heating zones, I just diddled the reset curve for the slab zone to run the circulator for that zone about 20 hours per day. For the upstairs zone, that uses baseboard, I put a little setback there (one degree). I could run that zone with more setback, but then I would have to raise the temperature of the water to get recovery in a reasonable time, and I choose to use lower temperature water there to get more condensing.



When I was still frustrating myself with setback, it would take about 5 hours to recover from a 4 degree setback.



That thermostat does have a couple of advantages.



1.) If I go for vacation in the winter, I can use a fairly large setback, and have it restore the heat 12 hours before I return. It can probably recover from that. If not, recover starting 24 hours before I return.



2.) It has a feature that tells me how many hours it was calling for heat on the current day, the previous day, and since it was last reset.

gerry gill

Thanks Tim, i'll have to look into that,

since were now using the TT's..it was a Peerless Pinnacle that was at that one job..that was really the only job we had a problem with..

Jean-David Beyer

Interesting Idea...

My fancy thermostat for that zone will estimate how long it takes to

recover from setback and turn the boiler on early to achieve the desired

setting at the time set. I am not sure how it arrives at that time. I

know the feature works, but is unsatisfactory. I am not sure it will

turn up the heat much more than an hour ahead of the time set, and since

it takes 4 to 5 hours to recover from a 4 degree setback, that does not

work. I have this feature on, but it makes little difference because I

do not set back the downstairs zone.



My boiler has an interesting featiure like you suggest. If the boiler runs

over BI minutes without being satisfied, it will raise the output temperature

10F or MAX, whichever is less. BI is user settable (if the user reads the

boiler manual) from 1 to 240 minutes. MAX is the maximum that the reset

curve can be. For my radiant zone, it is 120F. With the reset curve I used

last winter, it will raise the temperature less than 10F if the temperature

outside is 12F or less, and 10F if it is more. I have this feature disabled.



Now thinking about the downstairs (radiant slab) zone, I wonder how I would go about calculating whether I should use this feature or not. If I use it, I can employ some setback, but I will get less condensing by running at the higher temperature during recovery, lowering the efficiency. Does the energy I save by doing 4 degrees of setback exceed the energy I lose by running at the higher temperature? If I start the setback at 8PM or so, and my thermostat starts the heat at 4AM, will it be there by 6? I suppose I could figure that out. I know I have a chart that shows efficiency of my condensing boiler vs. return water temperature. I think this will be a lot of calculations, and using a lot of assumptions. I just might be obsessive to try the calculations sometime (not soon). I cannot imagine a normal homeowner would normally do this.



With a radiant slab, it is difficult to change the room temperature rapidly.

bob_46

Nasty pumps

I have a friend, a retired heating pro who lives in a house with the original overhead gravity system. It still has the original Ideal boiler with original V50 gas valve and a spring wound Chronotherm stat. I have stayed in this house a number of times and the heat is wonderful.

The system is dead silent , smoooth and has two moving parts, the diaphragms in the regulator and gas valve. I have wondered what I would do with a system like this if I had to replace the boiler. What do you guys think of the idea of making a gravity mod-con. It seems to me if you took a 6' piece of 16" pipe welded a plate on each end to make a vertical tank. Weld nipples at the top and bottom to match the pipe size of the gravity piping and then a couple of close spaced nipples near the bottom of the tank to accept

the supply and return from a mod-con. Naturally the mod-con would have a pump. I would control it with a simple wall stat which would give you indoor re-set. Kind of a pumped primary gravity secondary system.

Unknown

bob

It sounds like you mean a low-loss header system but gravity on the system heating side?

I would think this will work, but boiler short-cycling may come into play unless he has a BIG tank.

Then how do you stop gravity circulation when the stat is satisfied?

I would think he needs a valve with a very-low Cv factor to cut gravity circulation with the stat.

Charlie from wmass

Bob you could use a buffer tank.

By theory a properly set outdoor/ indoor reset system could keep the mod con down where you had constant circulation by gravity. I am not sure How much would be guess work but the idea of a gravity system was similar to a mod con with constant circulation in that it reduced the fire when the heat was up and opened the draft when things got colder. I would not mind doing this for my own house, a friend or understanding guinea pig but until I got it to work several times would not do it for full paying customers.