# in-floor heat w/ condensing boiler



## vanisle plumber (Feb 7, 2009)

Just looking for a little advice on an in-floor job using a condensing boiler. I am taking it over from the previous plumber who left town. The thing is I have only done simple single manifold electric boiler systems so far and want to make sure I pipe this properly. The house has 3 manifolds in 3 closets. I'll probably divide each manifold into 2 zones. Customer wants a high efficiency gas boiler. I'm looking at using a Veismann condensing boiler. This is where I am a little unsure of my plan, I'm thinking I need to use a primary/secondary system so that I still get the minimum flow through the boiler when there is only one zone running. Is this correct? The Veismann manual also recommends the use of a low loss header. I am assuming this is just to prevent "ghost flow" Don't know if this is a waste of money as I will be using actuators on the zones. Also planning on using just 1 circ pump on the secondary loop feeding the 3 manifolds and using the balancing valves to balance flow through the loops. Do I need to use a 3 way mixing valve to get the temp on the boiler supply down to a reasonable in floor temp. I'd appreciate any input/advise any of you have. Thanks,
James


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## futz (Sep 17, 2009)

No problemo! Just do this: :laughing:









But seriously, don't actually do it like that unless your system is like that one. If it's all radiant you DO NOT need a mixing valve, or those differential bypasses. There are a few more things I could say, but I have to go to work now. I'll type some tonight.


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## vanisle plumber (Feb 7, 2009)

Nice work!! What's the pressure differential bypass for? The system I'm doing is just in-floor but I thought the 3 way mixer might be needed to get the boiler suppy temp down. But maybe with using a modulating boiler I can set the temp low enough for in floor. I have not decided whether to use watts manifolds with actuators on each loop or make my own manifolds and use zone valves. Do you do a lot of boilers/heating? I would like to do more myself but never got any experience during my apprenticeship and now I've gotta learn on the fly as I pretend to know what I'm doing.


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## Nikolai (Dec 17, 2009)

With a modulating boiler you'll be able to adjust the boiler heat setpoints, no need for a mixing valve as posted above.


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## ZL700 (Dec 8, 2009)

Look closely it appears to be a 2 temp system, pump and zone valves close to right side of boiler looks to be non mixed, thus probably the higher temp requirement


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## futz (Sep 17, 2009)

ZL700 said:


> Look closely it appears to be a 2 temp system, pump and zone valves close to right side of boiler looks to be non mixed, thus probably the higher temp requirement


Yup. A few baseboards upstairs. It wasn't my idea - I hate the things. Kind of a waste of a high efficiency boiler, but it should still be at least somewhat more efficient than a normal cast iron, I guess.


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## Scott K (Oct 12, 2008)

Futz, Downstream of your 3 way mixing valve on the moderate water temperature side it looks to me (correct me if I'm wrong) that you have a Grundfos Pump, and then downstream of your Grundfos Pump you have a differential bypass valve coming off a tee. Now it appears to me by your picture - tough to see - that the differential bypass valve is feeding water into a tee. One leg of that tee pipes into the cold side of the 3 way mixing valve, the other pipes into another tee which are the returns from what I'm guessing are your radiant zones. Again correct me if I'm wrong.

If I am seeing this right, when your differential bypass is bypassing some water, which is most of the time during the heating season since not all the zones will be open at the same time, how can you ensure this warmer bypass water does not affect the ability of the cooler return water at getting to the 3 way mixing valve to throttle down the temperature??

I"m also trying to figure out why you didn't use an Alpha? It's as much or cheaper than a 15-58 and than a bypass valve and some fittings and looks cleaner to boot.


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## futz (Sep 17, 2009)

Scott K said:


> Futz, Downstream of your 3 way mixing valve on the moderate water temperature side it looks to me (correct me if I'm wrong) that you have a Grundfos Pump, and then downstream of your Grundfos Pump you have a differential bypass valve coming off a tee. Now it appears to me by your picture - tough to see - that the differential bypass valve is feeding water into a tee. One leg of that tee pipes into the cold side of the 3 way mixing valve, the other pipes into another tee which are the returns from what I'm guessing are your radiant zones. Again correct me if I'm wrong.
> 
> If I am seeing this right, when your differential bypass is bypassing some water, which is most of the time during the heating season since not all the zones will be open at the same time, how can you ensure this warmer bypass water does not affect the ability of the cooler return water at getting to the 3 way mixing valve to throttle down the temperature??


I set that bypass to only open when all radiant zones are closed. It's only there because the radiant and baseboard pumps are switched together (you either fix it with controls/wiring (somewhat difficult) or you fix it with piping (relatively simple)).



> I'm also trying to figure out why you didn't use an Alpha? It's as much or cheaper than a 15-58 and than a bypass valve and some fittings and looks cleaner to boot.


Heh :laughing: Mr. K, the Alpha salesman. :laughing: Didn't think of it. You're right, I sure should have done that on this one. I'll try to remember that for the next time this contractor does this foolishness. Would have been nice not to have to squeeze that bypass in - I was crowded enough already, what with the stupid gasfitter using up half the wall for stuff that should have been piped nice and compact in the front corner by the boiler.


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## futz (Sep 17, 2009)

vanisle plumber said:


> What's the pressure differential bypass for?


There's two of them. One for the radiant and one for the baseboard heat. Both of those pumps are switched together. So if all radiant zones are off and the baseboard is calling for heat (or vice versa) then the unneeded pump needs to be able to pump to somewhere, so it pumps through the bypass to the return.



> The system I'm doing is just in-floor but I thought the 3 way mixer might be needed to get the boiler suppy temp down. But maybe with using a modulating boiler I can set the temp low enough for in floor.


Condensing modulating boilers are totally happy with nice cool returns. Unlike an old style cast iron boiler, where condensation corrodes the vent and heat exchanger, modcons use condensation to reclaim waste heat from the exhaust (latent heat of vaporization). This is why we can use plastic pipe for venting.

Most have outdoor sensors so they turn the flame down and heat less when it's warmer outside. They're made to run at lower temps whenever possible. So they're a perfect match with radiant heating.



> Do you do a lot of boilers/heating?


Quite a bit. Been doing hydronic for 20-some years.

If you want to ask heating questions of someone who knows more than me, ask Scott K. He and I don't always agree on how things should be done, but he's an expert at hydronic.


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## Scott K (Oct 12, 2008)

Hydronics & especially Boilers, are an addiction for some people.


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## mtfallsmikey (Jan 11, 2010)

Get Dan Holohan's books: "Pumping Away" is good, also has good steam/primary-secondary piping books.


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## ZL700 (Dec 8, 2009)

mtfallsmikey said:


> Get Dan Holohan's books: "Pumping Away" is good, also has good steam/primary-secondary piping books.


Very true but wish to get in deep go straight to Siggy's books


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## Scott K (Oct 12, 2008)

ZL700 said:


> Very true but wish to get in deep go straight to Siggy's books


I have Siggys & Dan Holohan's books as well as several other books & manuals from other authors and I can tell you that without a doubt you should read Dan Holohan's books long before you even consider Siggy's books/articles. Both Siggy & Dan both know their sh*t but Dan's books explain it in a much easier, plain english fashion (what they are geared towards specifically) that will really help the average joe see it for what it is, and if you're still not satisfied, or crave more then you might want to look at Siggy's stuff. 

Learning technical stuff revolves around learning "concepts." Sometimes someone needs a concept explained to them in a sort of "rationalizing way" (or in more than one way) to help them see the light. Dan's books do that and are geared that way more so; Siggy's books are more geared towards a guy who is looking for a sort of mono-tonish fact based technical literature with some stuff that may still go way over your head at the end of it.


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## Greenguy (Jan 22, 2011)

Siggy's textbook is great for reading up on small items but it also tends to make me tired. I've seen dans books heard they are spot on, but haven't picked them up yet. My self I donated my time early on working nights and weekend with a hydronics guy was wicked learning. 

I have a couple of Hvac mechanics i work with wanting me to do the BCIT A gas next year, we'll see.


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