Gravity Hot Water Boiler Replacement???

Jed_2

I've been searching for guidelines for a gravity system boiler replacement. I have not seen the system( it's over 100 miles away; we have a large geographical service area), but am told it's been working fine for over forty years( waaaaay Downeast Maine). Existing boiler is an American Standard C.I.(AL3???) Will be replacing with an 8W3T Smith. I have read Dan's articles on conversion to forced circulation, but this is not a conversion.

What considerations might I look for with this conversion. We are not putting in a circ. Leaving the system as it is. Does boiler water content differential come in to play? I can't see any other issue, since gravity works on WTD. Contractor is not sure even if this is upfeed or downfeed system.

Any thoughts guys?

Thanks in Advance

Jed

Al Letellier

gravity hot water

I would have reservations using the Smith boiler. Because of water content, not the quality. Typically a gravity system has a lot of water and if you're going to keep it gravity, use a boiler designed to handle the thermal stress. The Buderus 215 is an ideal candidate along with the Viessmann Vitola. The later loves cold return and can handle all you can give it.
When we convert a gravity system to forced, especially with a low mass boiler, we always go Primary/secondary with constant circulation and outdoor reset. Done right, they'll never know the difference in comfort level or efficiency(except lower fuel consumption.
We do a low of these conversion here in Portland area. Good luck.

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smoore

could you give some more information on constant circ. and outdoor reset.

Al Letellier

more info on gravity system

Sure. The great thing about gravity hot water systems is how long the radiators stay warm. When you convert to forced circulation, the inevitable conmplaint from the customer is "How come the radiators get cold? They never did that before." By using constant circulation with outdoor reset, in a primary/secondary set-up, the rads are constantly warm, but only as warm as needed to maintain desired set point. The customer feels the warmth and no complaints.
Just tie the supplies together, tie the returns together with some means of balancing flow and tie them together with a primary/secondary setup to the boiler and a system pump. Use a TEKMAR or similar control to maintain setback system temp and start/stop the secondary pump to the boiler on demand. Easy as pie. It's a little more complicated if you use an indirect, but it can be done quite nicely.
Email me directly if you need more assistance. Glad to help.

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Jed_2

Good system, Al, But.....

How many Viessman boilers have you bid, and won, under the HEAP Program? Just curious.

Jed

Al Letellier

gravity

I don't even know what HEAP is,but I get the point. You can use any good boiler with this type of system. The primary purpose of the primary/secondary set-up is to protect the boiler from the thermal stresses. We've done many with our favorite boiler, the Weil Mclain line. Gold and GV boilers work great with this set up.

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