Boiler water temp

Discussion in 'Boiler Forum' started by t56tr, Sep 13, 2010.

  1. t56tr

    t56tr New Member

    Jul 19, 2009
    I have a 90 yr old house with hot water rads and a peerless mc05 gas boiler (dates 1991).

    The water temp hardly goes up to 130 -- this does heat the house, but the rads on the second floor and third floor finished attic barely get warm.

    How do I raise the water temp so its still hot on the higher floors?

    Someone said the aqua is not working right.

    Someone said the boiler is too small (the ratings on it are 93k 107k and max 130k)).

    Someone said change the pump speed.

    Someone said slow the water down by closing the main valve (s) down a bit.

    Some info:

    The boiler seems to have a roaring normal flame.
    The taco pump comes on when the boiler fires and runs till the boiler shuts down.
    The house is all one zone - 1st floor, 2nd floor, attic, and even old school baseboard rads in basement. The feed-pipes are enorumous cast iron 4" to 3" to 2" etc. The asbestos was removed years ago so they are not wrapped. The aqua stat is a Honey l8148e. Pressure is in the 12-15 cold -20 hot range. Upstate NY 2500 sq ft brick colonial.

    Any ideas? Thanks
  2. Dana

    Dana In the trades

    Jan 14, 2009
    Is the problem primarily during the October November & April May shoulder seasons, or is this a dead-of winter phenomenon?

    If the former, the response is slow because it's a high-mass system, with a huge volume of water, which takes time to heat up. Hopefully the boiler is plumbed with boiler-bypassing or similar to protect the boiler from destructive condensation during those long cold-starts. During sustained operation you don't want the water returning to the boiler from radiation to be colder than 130F or it'll be damaging the heat exchangers in the boiler. If it keeps up during the coldest nights in January the boiler is not undersized- it's probably "right sized" or slightly oversized for the peak load, depending on your insulation levels, glazing, and air-infiltration levels, but can't deliver a rapid-response on cold-starts due to the high thermal mass of the system. I have similar age & sized house in central MA, with double-hungs + storms that I've been tightening up and insulating. Without going hog-wild my design-day heat load has been reduced to ~ 30k, but it was probably 60-70K when I moved in. Your design temps are proably no more than 15% colder than mine, so a 75-80K true coldest hours heat load might be about right, or might be higher than reality if the place has seen insulation & window upgrades. Plumbed properly, high thermal mass in the system would be your friend for both comfort & efficiency.

    Depending on how the whole thing is laid out, you may need to plumb in mono-flow tees, partially bypassing the first-floor radiators to have more/warmer flow to the higher floors. Or there could be sludge/rust crud creating flow issues to the upper floors (but unlikely with big-bore pipe like that). If it's a manifold/loop configuraion, ball valves on the loops can be used to adjust balance. But without a system schematic it's really hard to say what the problem is, and how to fix it.

    Did it EVER run hotter?
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  4. t56tr

    t56tr New Member

    Jul 19, 2009
    It never goes over 130 anytime of the winter, fall, etc. It just runs a long time in the really cold months. I do not know the history the temp because I have only owned it two seasons and it has been like this since I moved in.

    The layout consists of of one large copper pipe (approx 1 1/4) coming out of the boiler, which Ts out. Each leg of the T is fitted to the large 4" cast with some huge iron adapter bushings. From there one section of 4" runs along the wall to the front of the house, one to the rear. The 4" reduces down to 3" then finally 2". Along the way every couple of feet there are 1" iron feeds that are joined in and go up to all the rads. There are alot of them, probably 15-20 on the front of house, 15 on back.

    For the return, there is an identical set up of 4" to " 3 cast etc, with all the 1" return feeds dropping in. The 4" returns from the front and rear of the house T's into the 1 1/4 boiler return pipe (where the taco pump is). The total lenght of the cast feeds and returns (the 4" to 3" to 2") is approx 200ft.

    To top it off, someone cobbed into those 1 1/4 copper pipes that come right out of the boiler ( right before it joins the 4") and ran 3/4 copper all the way accross the basement to some baseboard and all the way back .

    There is no bypassing or anything that I can see. Just one out on the boiler that t's to feed the rads, and one return where the water comes back. One circ pump, one expansion tank, one aquastst, one feedvalve, one thermostat on floor 1.
    Last edited: Sep 14, 2010
  5. Dana

    Dana In the trades

    Jan 14, 2009
    I'm assuming that this is the boiler series in quesion?

    If yes, running it with the RETURN water under 130F would probably destroy it over time let alone outlet temp of 130F. If it's been truly been running output temps that low and taking 110F water in, you will likely be in for a boiler-replacement in short years. At sea level with typical combusion-air mixtures on cast iron boilers the dew point of the exhaust is in the low-mid 120s F, so with return water near or below that dew point part of the heat exchanger plates will condense slightly acidic water onto the plate causing corrosion. The longer this goes on, the higher the corrosion level. (I'm surprised it's still working if that's the way it's been running since 1991.)

    If the aquastat relay normally runs the circulator pump constantly whenever there's a call for heat it could cause symptoms such as this in a high mass system. I believe L8148e is a high-limit-only device, that doesn't inhibit circulation while the boiler is heating up. The controls could be re-configured to inhibit the pump by running controlling the pump with a separate aquastat set to turn it on when the boiler reaches 150-160F or somthing, but the near-boiler pluming has to be configured to protect the boiler from thermal shock- 160F out is great, but not when you have 70F water enteriing the boiler- the thermal stress of such a large delta-T will destroy the boiler faster than condensation will. But even reconfiguring to allow the boiler to run at a temp & delta-T within spec for the boiler that won't fix your balance issues. Slowing the pump down for a higher boiler temp would create similar delta-T stresses on the boiler- don't go there without re-plumbing the boiler with a boiler-bypass or some other measure to mix return water with boiler output where it enters the boiler to keep the delta-T bounded (30F differences are generally OK, 50F almost never for cast-iron boilers.)

    This really calls for a professional on-site assessment, not a web-forum fix. I suspect the sizing is OK (but it might not be)- it's NORMAL for a right-sized boiler to run a greater than 50% duty cycle mid-winter. But a 20 year old boiler that may have been suffering condensation damage for years may not be worth saving at this point. The fact that it can usually heat the place with 130F water means you have sufficient radiator to take GREAT advantage of a high-efficiency modulating/condensing boiler if the system designer/installer is any good. Breaking into zones by floor (including the basement baseboards) would also go a long way to resolving balance issues within zones. You haven't reported your fuel use numbers yet, but DO (along with your zip code so we can correlated it to degree-day data.) Using an existing boiler to measure the heat load on a place is usually more accurate than any of the standard estimation methods using insulation levels & window area, etc., which will determine how much boiler you need when this one fails.

    Before pouring ANY money into reconfiguring the system, have a competent boiler-tech inspect the fire-side of the heat exchanger plates. If the corrosion is slight, it can probably just be cleaned up, and with some system tweaks it could go for another couple of decades. But if what I suspect has been going on proves to be the case, it's a basket case, and might not last the heating season. If it's bad news you REALLY need to find that out closer to September 15th than January 15th when corrosion from condensation finally burns through the heat exchanger, and all of the heating system water drains out onto the basement floor.

    If you end up replacing the boiler with a high efficiency version odds are pretty good you'll cut annual fuel costs by at least 1/3 (maybe more, if the existing beast has been fighing an uphill battle trying to get the heat through a half-inch of rust on the fire-side of the heat exchangers.) If there's any money in the budget, have them quote an indirect-fired tank for the domestic hot water as well. Try to suss out the heating contractors in your area BEFORE soliciting quotes- there are a lot of heating & plumbing contractors competent to do boiler swaps, but may not be all that great on the system-design end. If might be worth paying a designer to spec the system alterations, and get quotes based on the spec.

    Trying to balance a basement & attic zone to a first-floor thermostat control is an exercise in futility- it probably needs to be broken up into zones by floor to have any hope of consistent comfort. A simple boiler swap probably isn't going to do it.
  6. t56tr

    t56tr New Member

    Jul 19, 2009
    Yes that is the boiler - Thank you for all of the great advice so far!
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