Bypass I've not seen before

Cliff Brady

As an H.O. wall lurker for many months it has become a pasttime of mine to take a look at the boilers in when visting friends and neighbors houses to what kind of setup they have. One friends boiler has a bypass piping arrangement I don't recall seeing any where on the wall or in any other house. I will try to describe it as best as I can. It is two pipe gravity conversion and the boiler is boxed in pretty well but this is how it looks:

The boiler supply and return are on the side of the boiler. I assume the return is the lower connection and the supply is higher one.

The pump is pumping down into the return. Between the pump and the boiler return there is a tee with a 1 foot horizontal pipe to a tee in the vertical boiler supply pipe. There is a ball valve in the one foot section between the tees. The valve is about 40% closed. This arrangement doesn't look like it would mix much warm supply with cold return since return is under positive pressure at the tee from the pump. It is all cast iron piping. Here is a diagram.


return
pump********system supply

*|*******************|

*V*******************^

*|*******************|

*T---U-----BV-------T

*|*******************|

*|*******************BS

*BR

*=Ignore the asterisks, just spacing
T=Tee, U=Union, BV=Ball valve, BR=Boiler Return
BS=Boiler supply

The boiler is less than 15 years old and I am not sure of the make. Judging by the size of the boiler and house which is similar to mine and probably more energy efficient. I am guessing its 200-250kbtu/hr when probably 125-150k would do.

The real issue is it looks like there might be a lot of condensing in the flue or chimney as there is a crescent of rust and calcium deposits on the bottom of the flue where the flue enters the chimney. I covers the lower quarter of the flue and extends down the flue from the chimney about 4 inches.

It was installed by a well known company in town and I think they do the annual service also. I just want help my friend know what questions to ask when he gets it serviced/cleaned to make sure the condensing is under control and the venting is safe. I may educate him about outdoor reset but I am not sure about its effectiveness in an oversized high mass sytem like this.


Any thoughts or suggestions appreciated.

c

Unknown

It would seem

as if your friend has a system bypass installed. The purpose is to blend heated supply water with cool return water to help keep the boiler hot. This will assist in making the gravity conversion work while still providing a limited ability of the pump to circulate water to the system. I suppose that the question is........does it work OK? Does it look something like this?

Glenn Stanton

Manager of Training

Burnham Hydronics

Cliff Brady

Yes, except the pump

is above (upstream) the bypass tee on the return so it I would think the bypass would work in reverse since the water coming out of the boiler supply would be at a lower pressure due to boiler head loss. So in this arrangement I would expect return water to mix with the supply unless there was a venturi or something.

If the boiler is oversized I would think even with the bypass the boiler may short cycle and have a hard time getting out of condensing mode much of the time.

Mark J Strawcutter

boiler bypass

Sounds like boiler bypass (vs system bypass).

Some of the pump's output goes thru the bypass, some thru the boiler. On the other side of the boiler, the lower temp bypass water mixes with the higher temp boiler output water.

With boiler bypass you still have full flow thru the system, but reduced flow thru the boiler. This helps bring the boiler up to temp and reduce thermal shock and condensation.

With a gravity conversion, I believe a system bypass (as Glenn described) is more appropriate. Full flow thru boiler and reduced flow thru system. Like boiler bypass, it also brings boiler up to temp.

Mark

Cliff Brady

Thanks for the explaination.

Thanks for the explaination. That makes sense now.

Unknown

As Mark pointed out

If the pump is on the system side of the bypass, then you indeed have a "Boiler Bypass". This is what is generally called for in most installations....except a gravity conversion. This just reduces the flow through the boiler to keep the boiler up in temperature. You are better off with a "System Bypass" on a gravity conversion. This is a picture of a "Boiler Bypass". Hope this helps.

Glenn

Unknown

As Mark pointed out

If the pump is on the system side of the bypass, then you indeed have a "Boiler Bypass". This is what is generally called for in most installations....except a gravity conversion. This just reduces the flow through the boiler to keep the boiler up in temperature. You are better off with a "System Bypass" on a gravity conversion. This is a picture of a "Boiler Bypass". Hope this helps.

Glenn

Unknown

As Mark pointed out

If the pump is on the system side of the bypass, then you indeed have a "Boiler Bypass". This is what is generally called for in most installations....except a gravity conversion. This just reduces the flow through the boiler to keep the boiler up in temperature. You are better off with a "System Bypass" on a gravity conversion. This is a picture of a "Boiler Bypass". Hope this helps.

Glenn

Cliff Brady

About the possible condensation

in the flue, should the installers who still service the boiler take responsibilty for flue damage caused by condensation? I think not if they did a heat loss calc when the boiler was installed and the heat loss has been drastically reduced since, or if rain down the chimney is a problem. Or, might this be considered normal wear and tear?

BTW, there is an electric flue damper installed.

BillW@honeywell

Chimney problems

A Certified Chimney Sweep may be helpful in diagnosing and curing problems. Make sure you deal only with a Certified Sweep, they carry a photo ID with a number on it, ask for it. If one isn't listed locally, call 317 837 1500 for a referral. They have specialized training & expertise to deal with chimney issues like liner failure and moisture/condensation. I hope this helps you.

Geno_7

By pass

Want to hear a good one. My wife and I bought a 100 yr old house years ago. Cast iron radiators etc,. Being low on cash but able to get plenty of used parts I built a system. American Standard boiler C.I.,target wall, Beckett burner, 140psi pump, cut out black pipe, ran insulated copper,zoned the house with taco's including the bathroom, nice to wake up spring and fall to a warm bath!, screwed an Everhot 8gpm into the top of the boiler with a mixing valve, tee'd out of that to the zv's and the return after a flow check, the aquastat in the Everhot turned on the circ and burner and on a call for heat it went through the Everhot any way. Filled my hot tub with it and burned an average of 400 gallons a year. The people before were burning 1000, I checked. As far as I know it's still there.
Geno