Gravity Conversion

STEVEN MARKS

I am converting a gravity hot water sytem. I took the advice from the wall and I am planning on installing a taco mixing valve although it is not in the diagram.

I have a question about the piping.

The gravity system has 2 supply and returns. The 2 supply are 3" and 2-1/2" as are the returns. I was planning on reducing the 3" supply to 1" and the 2-1/2" supply to 3/4" and using a Grundfoss UPS 15-58 pump.

Is this correct?

Any suggestions.

Thanks

Jamie Hall

Pipe sizes are probably OK...

but you are going to have to have some means of controlling the balance between the two circuits.  With a single pump forcing, the water will go the easiest way -- and that is not necessarily where you want it to go.  Zone valves or two pumps... IMHO

Mike Kusiak_2

Pipe sizing

Pipe sizes may be a bit small. Here is an quote from Dan's article on gravity systems:



http://www.heatinghelp.com/article/332/Gravity-Hot-Water-Heating/72/Gravity-Hot-Water-Heating-FAQ



Q: How will I know what size pipe to use on the new boiler?

A: A good rule of thumb is to take the largest pipe, divide it in half and then drop one size from that. That becomes the size of your new near-boiler piping. For instance, let's say the largest pipe is 2-1/2" (if there are two inlets and outlets, you only have to consider one of them). Divide that in half and to get 1-1/4". Now drop down one size to 1" and that's what you'll use all around your new boiler.

If your largest size happens to be two-inch, pipe your new boiler in 3/4". It will look odd, and it might make you feel uncomfortable, but it'll work. Different systems call for different piping techniques. One size doesn't fit all and a gravity conversion is definitely different from a brand-new, forced-circulation job.

It might make sense to go up one pipe size on all the new piping

STEVEN MARKS

pipe size

Mike I also read the article. I felt that 1-1/4 secondary header would be the same as the near boiler piping described in the article.

The boiler only has 1" tappings for the supply and return. The velocity may be hign in the short pipe lengths but the pump should be able to overcome the little resistance.

I was trying to feed the 3" with the 1" and the 2-1/2" to try and balance the flows. I was also planning on installing ball valves to further balance if needed.

On the other hand if I was totally sure of myself I wouldn't have posted in the first place.

Thanks

STEVEN MARKS

pipe size

I think I will take your advice and upsize all the secondary piping to the next size but leave the primary piping 1".

Thanks

Ironman

A Couple of Things

First, may I ask why are you installing a boiler that's more than 1&1/2 times your heat loss? If someone has told you that you must do so because of the volume of the old pipes, that is a mis-conception - size it according to the heat loss including any allowance necessary for piping. I would also recommend wrapping any large pipes. Even a couple of laps of bubble wrap will make a difference.



Second, I would connect the indirect parallel off the supply and return of the boiler, not off of the primary loop. Put its circ. on priority and you're good to go. You'll need a circ. in the boiler loop also.