Print

[woodman]

Ok plumming experts, here is my question. I have 3 hx's in a series. The first pulls 10 degrees, the second pulls 20 and the third pulls another 10. Not often do all 3 call for heat at the same time, but when they do how am I suppose to keep return temps up. If it was set up off a manifold it would be no different unless it would only allow 1 zone to circulate at a time, right?

[Scott7m]

Is the water heater also in the same series??

Is one of them rarely used?

I get nervous when I see folks do 2 and a plate, only thing that makes it ok sometimes is the up stairs one rarely kicks on

[woodman]

The first is dhw, then the main furnace, and finally the garage. Mornings are probably peak demand with showers, the house coming up to temp, and the garage opening a couple of times.

[Scott7m]

What size pump are you running?

Have you ever checked return temps when all 3 were running? 

[woodman]

Its a Bell and Gosset 36. No I havent checked when all 3 are calling for heat.

[Scott7m]

That would be interesting to see that,
May be a good test

[woodman]

Assuming it is 40ish what would be the fix?

[Scott7m]

More flow would be the simplest

Bigger pump, or another in series

If your over 140 your fine, plus it would be a rare occassion


I just think it's gonna be under 140 with all 3 cranking

[woodman]

I am pretty sure it will be under 140 at some point of the cycle, but like you said, it is rare for it to happen and I really don't like the idea of a bigger/extra pump. Since it is probably happening when the wood is mostly gone, or has at least went threw multiple burn cycles, would that cut down on the moisture available in the firebox? 

[Scott7m]

Yea it would def help that situation

Check it at different times so you'll know tho

[woodman]

OK I will check temps tomorrow.

[woodman]

With all 3 running I am pulling a delta t of 43*. I went out and looked inside of boiler, I couldn't see any signs condensation. Is it obvious to see, or does it form behind the creosolt? 

[Scott7m]

It's not always obvious to see, but you are probably ok,
I think the pl36 is helping you out and keeping you out of danger for the most part

As long as it is a rare occurrence

[woodman]

Maybe I am off on this but if all 3 HX's are in series wouldn't it be better to have a loop with closely spaced tees tying them all together?

I don't know for sure, but it seems like that would make the water slow down even more, and the water would be even colder after it went through the hx's on its way back to the boiler. The only way I see around this is to put a buffer tank in the basement with multiple ports. Then plumb each hx on its own zone with its own circulator and zone valve. I don't like the cost and complexity of that thought though. In all honesty I was never worried about any of this until all the threads about boiler failure and low return temps.   

[Scott7m]

Close space tees would keep flow up, but were talking more pumps and all that, nahh

You could however use an aquastat on the last heat exchanger in the garage that would only allow your garage to be heated when the water temp was let's say 155 or higher, for example if the strap on had 140 degree water already coming to it, it wouldn't allow the garage to call for heat until it was a safe number