Question

Mpj

Went to look at a job today to install radiant in a kitchen, went in the basement and found a kinda new oil boiler. The existing system is a old two pipe gravity system (i think) with 4" supply and return piping (split on both sides of basement) hanging low.

The owner asked if there is any upside (as in system efficiency) to remove these pipes and install a "home run" system. Besides the head room and heating up less water I could not think of a reason to justify the cost of removal and new installation of PEX tubing.

She says the system works great the house heats up well and she is comfortable. I said she could have zoning ( room by room or by floor).

If anybody can add their 2 cents on why to convert I would like to hear.

Thanks.

STEVEusaPA

Answer..........

Well actually, more questions....new boiler with the original gravity piping?  Is there a circulator, or still gravity system?  What kind of heat emiters? Pics always help, but a more complete description of the system will get some more responses/advice.

Mpj

Questions

No pictures. System has a circulators (some sort of injection, I think). 1" copper supplying both 4" supply pipes. Cast iron radiators through out the house, expansion tank (and one next to the boiler) on the third floor with pipes leading up into the ceiling which leads me to believe that it is an open system.

icesailor

Question?

Here's a way to help the system.

In no way do I think it is practical in time and money to do what the owner thinks. A better way would be to split the boiler connections to the gravity system with a 4-way mixer. Then, the old gravity part can be "pumped" but still act like the gravity system that it was designed and installed as. The system water temperature will most likely be very low and the radiators will be "cool" rather than some being extremely hot (the ones closest to the circulators) and the ones that are the farthest away (from the circulators.)

Then, you can run the boiler and indirect (if installed) at whatever temperature you need and then add the radiant zone with hot water at whatever temperature you need with a mixer to give you proper panel temperatures.

I personally feel that this is the only reasonably priced way to marry a high mass system like a gravity system to a low mass heat source. I always try to make something work better than to try to re-invent the world.

The pipes in the ceiling that you think go to a gravity tank in the attic are most likely capped off. You can't really pump to a gravity tank although I've seen it done. A tip off is, Is there a Pressure Reducing Valve on the cold water fill to the system? And does the PRV have one of those Pressure Relief Valves as part of it? If so, that was installed when the pumps went in. It's a closed system. Look upstairs on the top floor in a closet for the remains of the pipes or old tank. Or, it's in the attic. The signs are there somewhere, where it was.

I've dealt with a lot of old gravity systems. I never saw a pumped one that worked worth a darn when fired with an oil burner or a gas burner. I did one recently with the 4-way mixer and it is the absolute perfect fit on a gravity converted to pumped system.

If someone calls you on the phone, they are willing to spend money. It's your job in business to figure out how much money they are willing to spend and for you to give them the best service and product for their money. I find that most potential customers will balk at the whole nine yards but will be interested in seriously improving what they have. Especially if the system gives them better comfort. And they can then spend extra savings money on heat loss improvements. Like insulating all those big gravity pipes. 

And if they decide to change the boiler in the future, it is all set. And if you are still around, will most likely be the only person they call.

It's called "Planning For The Future".

Mike Kusiak_2

If it ain't broke dont "fix" it

"She says the system works great the house heats up well and she is comfortable".



If the system works well as is, why would you want to change it unless the gravity pipes in the basement were in the way. The high water content in itself is not a problem, but as Ice says you could insulate the basement piping to reduce heat loss. Ripping out the gravity piping would not gain you efficiency in itself.



If there were a comfort problem, you could go with the 4 way mixing and outdoor reset as suggested, but these old gravity system have there own sort of inherent reset, due to the high thermal mass and low temperature radiation. If she wanted zoning in certain areas, adding some TRV's would be a much simpler solution.