Can i use 3/4'' piping for home boiler system?

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Old 03-16-11, 02:45 AM
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Can i use 3/4'' piping for home boiler system?

i can use up to an inch but i was wandering can i use 3/4'' piping as long as u use brazed plate heat exchangers for every heating circuit and a high rpm main circulator and every zone have a slower speed circulator taking heat to the needed areas from the heat exchangers? i may have 10 zones if i get rid of forced air and a green house backyard unit heater. can i get away then with using 3/4'' pipes? just copper is to expensive. or is 1'' better if the 10 zones will be 3/4''? also 1 1/4'' pipe but stss co inc tanks seem to go only up to 1'' pipe.
 
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Old 03-16-11, 05:40 AM
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Why do you want to use plate heat exchangers? What is your heat loss? What does the manufacturer of the boiler recommend for near boiler piping?
 
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Old 03-16-11, 06:30 AM
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my heat loss on the coldest days is 70,000 btus. my home square footage is 1500. and the boiler has no recommendations. i was thinking of flat plate heat exchangers to prevent pressure drops. but i am thinking of future addons which will bring it up to 6 to 10 zones.
 
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Old 03-16-11, 07:14 AM
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If your house is 1500 sq ft and a heat loss of 70K I think I'd put money into weatherization to get it down to 40-45K loss. The number of zones you're contemplating sounds like overkill and can lead to excessive short cyling of the burner leading to premature component failure not to mention the cost of all those zone valves or circs and controls.

I don't follow your thinking about eliminating pressure drops by using plate exchangers since there will be pressure drops on both sides not to mention an additional circ and control for the radiation side of each. Maybe I misunderstand what you said?
 
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Old 03-16-11, 07:25 AM
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You don't need plate heat exchangers to deal with pressure drops. There are piping strategies to deal with that. Why do you want so many zones?
 
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Old 03-16-11, 03:48 PM
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Ditto what everyone has said so far... just as a reference point regarding your heat loss:

70K BTU by 1500 sq ft is almost FIFTY BTU per square feet! That's HUGE! Are all the walls standing? all the windows in? I would be surprised if your heat loss is even 50K ... unless of course you are missing walls or windows.

Insulation and weatherization to reduce heat loss is by far, hands down, the BEST fuel saving measure you can take. Don't underestimate it's efficacy! And, IT'S FUEL YOU ONLY PAY FOR ONCE!

You are worried about the price of copper yet contemplating purchasing heat exchangers? Have you looked at the prices of them?

More zones does NOT save fuel. It wastes money.

As for the pipe sizing... there are a few rules involved:

You want the VELOCITY of the water in the system between 2 and 4 Feet per second.

3/4" pipe can flow about 4 GPM and 1" about 8 GPM at that VELOCITY.

For each GPM you can figure on moving 10K BTU through a system.

It follows that 3/4" pipe then can move about 40K BTU, and 1" about 80K BTU.

Generally speaking, you can feed TWO 3/4" loops with the next size up pipe (1")

The bottom line here is that you need to know how many BTU are needed in each zone and size the pipe accordingly.

Ten zones is probably seven too many.
 
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Old 03-16-11, 09:38 PM
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my heat loss is really 30,000 btus max. but how doi figure out what pipe size i need?
 
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Old 03-17-11, 05:41 AM
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I think that was answered earlier,
flow velocities need to be no more than 4 feet per second.
There are charts that will tell you your velocity and headloss per 100' of what ever pipe you want to use for a given GPM flow.
GPM flow is determined by the load you are serving, and it's delta T
 

Last edited by NJT; 03-17-11 at 05:28 PM.
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Old 03-17-11, 05:27 PM
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How did your heat loss go from 70K to 30K almost overnight?
 
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Old 03-18-11, 01:16 PM
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heres a you tube video and it has 12 zones coming off from an 1'' pipe. watch this video and tell me if thats correct.

YouTube - Buderus boiler installation - twelve zones
 
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Old 03-18-11, 02:28 PM
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Good golly what a waste of money.

BTW, the text says it's 1-1/4" main, not 1" ... but still, that ain't right.

For one thing, having a pumped zone for each room is just ridiculous. What's the point?

And, if each room is on it's own zone, why does he even need 3/4" pipe feeding each room...

The whole concept is just wrong.
 
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Old 03-18-11, 02:33 PM
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How did your heat loss go from 70K to 30K almost overnight?
 
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Old 03-18-11, 04:48 PM
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Originally Posted by TheHandyMan View Post
heres a you tube video and it has 12 zones coming off from an 1'' pipe. watch this video and tell me if thats correct
"I saw it on the internet. It must be right." Wrong. That is incredibly poor design and the customer will be paying for it forever.

For the pumping and electrical, try this instead: ContractorMag -- Dave Yates

For pipe sizing, consult any decent book on hydronics.
 
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