Help...

John_134

If a relay were used, would that be an plumbing/heating professional or an electrical professional?

John_133

Looking for advice re. dual heating system with backdraft prob

I bought a house that is approximately 90 yo, wife loves it, wrinkles and all. Currently it has two gas boilers which vent to a single flue. Seperate zones, Boiler One is steam and Boiler Two is hot water. Both are very old but when tested, they do function well (previous owners ignored the condition and ran them in this config for years).

The problem:
The exhaust flue for venting is 6 inch aluminum with no blockage. Boiler One has 7 inch exhaust reduced to 6 inch and Boiler Two has 6 inch exhaust. When run independently, they operate fine but naturally, when run together, they both backdraft.

Please note, the system is not currently being used but would like to resolve this issue as quickly as possible.

Financially, we would like to replace both with single unit but afraid it would be too costly given the different configurations. Instead, we're considering replacing one and venting direct externally but this is not a good solution as when the other dies, it will need to be replaced and we're left with two boilers again.

Looking for any and all suggestions/ideas.

Thanks,

John

hvacfreak

well...

Are these flues " tee'd " together or do they enter a masonary chimney seperatly ? They need to enter the main ( masonary , b-vent , whatever ) seperatly. A temporary solution would be to install a relay on the steam burner that opens the call for heat on the water burner ( not allowing the water burner to fire if the steam burner is firing ). Kinda cheesey thing to do , but it will get you by until your change-out. - freakorama

John_133

Reply

hvac,
Thanks for the reply. Below is a crude diagram of current config. You mentioned that they must seperately vent into the masonery. IF the liner to the chimney is six inches, even if I could get them both in seperately, wouldn't that still create a choke-point (i.e. starting pt of backdraft)?
Thanks again,
John
ps. Cannot insert picture; but both the Steam and Water exhausts connect to same 6 inch pipe that connects to the chimney flue.

Dave_4

John

You must provide us with more information. You say these are "old" appliances. How old? If you can get make/model manufacturer, most especially I need the BTU's, the height of the chimney, the lateral distance (length) of the appliance(s) from that chimney, whether or not its a cold chimney (that being an exterior one with 3 cold sides exposed to the out of doors). I would also need to know if there are offset(s) in the chimney and what of their lengths.


Say in a "best case scenario" without knowing the above. The appliances I'll use will be mid-efficiency 80% Category I. If I look at Weil-McLain's EG-50 (steam) with an 175,000 input btu (the smallest one with a 7" flue) & Weil-Mclain's CGa-5 (water) with a 140,000 input btu (the smallest one with a 6" flue). This gives me a total of 315,000 btu's. Now, if you look at the 2003 International Fuel Gas Code, Table 504.2(2)(this is the table you use for sizing with corrugated liner systems or B vent) @ 20' foot in height and -0- zero lateral distance, you get to vent 306,000 btu's (or ALREADY TOO SMALL),

right?

wrong!

According to Section 504.2.7 you must reduce that 306,000 by 20% or 244,800 because you used a corrugated liner.

So. now,

If you know look at Section 503.5.5 and apply "thee ol' rule of thumb" or 50% rule, you will need to use the size of the larger outlet plus 50% of the area of the smaller one.

Lets do the math....(I'm not good at math) for the (6") six inch.

A= 3.14 x (3in) x (3in)

A=3.14 x (9in)

A= 28.26 in sq.

50% of 28.26 in = 14.13 in

add this to the larger flue outlet (7") seven inch or 38.46 sq. inches

total = 52.59 sq. inches.

I would say you are in a pickle because even (8") eight inch is 50.24 sq. inches.

Trying to vent both these appliances atmospherically is dangerous as I'm sure your already aware. I'd suggest getting a "very sharp" venting guy or an engineer to calculate for you a "new" forced draft system or possibly a exhauster/booster fan interlocked to the appliances.


Good Luck!


Robert O'Connor/NJ

STEAM HEAT

HELP PLEASE

I hope someone can help me, I have old iron Radiator's for heat, steam heat run by Gas Furance. I am haveing problems getting my radiator to heat up, a friend of mined said to bleed them which we did and all the radiator's in my house got hot as long as I bleed all of them. but than it goes away, My Furnace guy tells me I don't have to bleed them.I dont know who to listen to anymore don't want to pay all kinds of money finding the right person. is there someone out there that can help me out, I am from Mass. Worcester county.

Thank You

brucewo1b

You have a venting issue

Measure your length and diameter of your staem mains and someone will tell what size main vents you need. Are there main vents there now they should be after your last riser and 15 inches before they drop down. once that issue is taken care of we can work on rad vents. I am assuming this is one pipe steam and not gravity hot water. when you bleed the rads do you get steam or water??