Gravity hot water system

KingEdward

I have a customer that would like to switch from oil to natural gas.  They have 3 floors if  gravity radiators. The original tank in the attic has been disabled and there is a steel expansion tank in the basement ceiling.  It also has a pressure reducing valve.  Todays boilers only have 1 1/4 boiler tapings, I'm worried about adding a circulator if the house would not heat as even. I know i would have to add a bypass line or use primary/secondary piping. Should i consider using a steam boiler for the larger tapings converted to water and keep it gravity? The circulator in the photo was a basement zone and will be disconnected. 

Ironman

We do gravity conversations frequently and also use a mod/con. They work great together if you know how to marry them.

Don’t worry about the larger piping sizes: that was only necessary for gravity and pumping it won’t be a problem if everything is sized correctly.

One thing to look for is orifice plates in the inlets of the upstairs rads. Remove them and put them in the downstairs rads. This is necessary because the flow dynamic has changed from gravity to forced flow.

Have you done a load calc? That’s a must as well as a radiation survey.

KingEdward

Thanks for the comment,  I have read about the restriction plates you mentioned, i have not opened a union as of yet because the job is only in the planning stage.  I did see the valves are only 3/4". A heat calculation will be be done as well. I was trying to make  A decision on whether to keep it gravity or make it a pumped system.

Ironman

Circulators aren’t that expensive and may actually help system performance.

The gravity piping is 100+ years old. Over time, the interior of the pipes can become rough and smaller in diameter. That causes the flow to hindered and reduced. Converting it to forced flow eliminates that issue.

Alan (California Radiant) Forbes

I like the idea of keeping the gravity system and using the larger tappings of a steam boiler, but have never heard of it being done.

KingEdward

Converting a steam boiler to hot water isn't very difficult, basically replacing the steam pig tail and pressuretrol with an aquastat.  Replace 15 lb relief valve with 30 pound and gauge to T&P  Gauge. In my case i would not need to add on a circulator.  

mattmia2

You only need to move enough water with the circulator to move the needed amount of heat which is far less than the maximum capacity of those pipes. I don't think the manufacturer would want to warranty a new boiler set up as gravity hot water. Pumped conversion is done all the time. I think there is an Idronics that talks quite a bit about it.

pecmsg

One advantage of a circulator is being able to Zone areas. 

Another is indirect HW heater. 

EBEBRATT-Ed

@KingEdward

I would not go back to gravity now, it's forced hot water now. How does it heat with the existing boiler?

I see at one time it had an HB Smith boiler, they left the old header in place @Jamie Hall

Do a heat loss calculation. @DanHolohan tells how to do a gravity conversion in one of his books "How Come"

I would do P/S no matter which boiler I installed.

I would try the system without touching orifice plates first. Since it's already FHW it may be ok as is

pecmsg

The house were living in HAD Hw Gravity system. I will say most comfortable / Even heating system I've ever seen. Also the most expensive to operate!

Zone it
1st floor
2nd floor
3rd floor
Domestic HW

Alan (California Radiant) Forbes

I would not go back to gravity now, it's forced hot water now.

@KingEdward said, "The circulator in the photo was a basement zone and will be disconnected."

As far as zoning an old gravity system, it's not that easy. One of those take-offs from the header at the boiler may serve radiators on multiple floors.

Zman

I say pump it. Buy an antique car if you want a fun project.

KingEdward

@EBEBRATT-Ed Thanks for the comment, ill check out the book how come. The system is gravity now not pumped. The circulator is only on a disconnected basement zone. I wasn't interested in making it more that 1 zone. Im only looking for opinion on if it will still heat 3 floors evenly with a circulator.  Ed

HVACNUT

Primary/Secondary piping, constant circulation, TRV's, ODR, and a regular (STUPID) thermostat. 
Is that a good combo?