I am dormering my house and will have 4 bedrooms upstairs now. I want to put a thermostat in each room so everyone’s comfortable. I am going to run a supply and return of 3/4″ PEX to each room that will connect to baseboards. Down in my boiler room I will connect the PEX runs to a manifold of zone control valves. Is this a good idea? How much can 1 circulator handle, if every room is calling for heat? Also how can I be sure my oil burning furnace can handle it. I have three zones on it now, one is already for the existing 2 bedrooms, I figured adding two more rooms wouldn’t matter that much. What do you think of using PEX?
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That's a lot of issues.
I would suggest doing more research before you proceed, because I suspect this is far more complicated than you are expecting.
The best place to start IMO is with this textbook:
http://www.hydronicpros.com/publications_content.php?id=24
Not cheap, but worth every penny. Even comes with design software.
You need to do a heat loss calculation on your structure to find out if your boiler is up to the task, and to figure how much heat energy each of your rooms need. Slantfin offers a free heatloss calculator on their site.
In most cases, boilers are oversized to an extent that the additional load you describe would be handled easily.
One issue right off the top is that PEX is not particularly well suited to high temperature applications. Most oil boilers output 180 degrees (common range is 160-190). 180 degrees is the top of the range for PEX, and data suggests you can go higher, but the tubing gets very "droopy" at those temps. You can mix down the temp with mixing devices, but you may not be able to get enough output with your baseboards at lower temps (baseboards are generally used for high temp applications).
With a zone for each room, you may need to worry about "micro-zoning", meaning that if only one room calls for heat, the boiler may short-cycle badly.
You need to decide whether to zone with valves, circulators, TRVs (thermostatic radiator valves)...
Those are a few things to think about, but I could go on for pages about the considerations facing your project. Just too much to cover. This is not to say that you cannot gain the skills if you are willing to make the investment, but most people would probably get overwhelmed and hire a pro.
If I adequately supported the PEX would it work? I'm worried about it melting or getting hot enough where it'll pop off the connectors. Then again most water in the heating system is only around 20psi right? Maybe I'll gang 2 rooms together on a zone, two of the rooms are identical in size, then I'll use circulators. Is the micro-zoning you mentioned harmful to the boiler? It is a brand new cast iron Burhnam boiler with a Reillo burner.
Beyond the rest of the design issues, which I'm not getting into at the moment, for high temp use PEX-AL-PEX. flexibility/continuity of PEX (more or less), stiffness and limited expansion of copper. Ideal for baseboard.-------------------------------------
-=Northeast Radiant Technology=-
Radiant Design, Consultation, Parts Supply
http://www.NRTradiant.com
Is that type of PEX as easy to bend and snake thru walls as the other stuff I'm thinking of?
"Is the micro-zoning you mentioned harmful to the boiler? It is a brand new cast iron Burhnam boiler with a Reillo burner."
Conventional boilers have 2 "speeds". High and Off.
Let's say it is a 150KBTUH boiler, and you have 4 rooms (ind. zoned) with only 5KBTUH heatloss each on a mild day. If only 1 zone calls for heat, the boiler may not even get up to normal operating temperature before it satisfies the call. This leads to inefficent combustion, which leads to soot buildup, and condensation which leads to corrosion. That all assumes you have enough flow.
If you do not have enough flow through the boiler, it may bump against its high setpoint and shutdown.
There are ways around these problems through design, but it gets very complicated in a hurry, since there are so many possible approaches.
csnow has covered most of the facts pertaining to your questions. I will only add one thing, you probably have very little excess capacity in your boiler. Ever since energy went through the roof most contractors size right to the heat-loss at the time of install. Luck with your project.
Edited 3/3/2006 3:16 pm ET by Shacko
I concur on the TRV choice, over zoning each room. Unless the zones need different heat (below grade vs southern exposure or something) I'd say put everything on the second floor on one zone, and use the TRVs in each room.
I'm using baseboard so how do I hook up a TRV to that?
What type of baseboard? Cast iron, copper finned, decorator? I'd imagine that you will need a slightly longer run of piping on the inlet side. But that is certainly a good question, and one to take up with the manufacturer of the units that you are considering.