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FHW heating efficiency

ratio Member Posts: 3,696
Ok, my gas bill is now double that of this time last year, so I have orders to get it lower. I've got a 5 section Peerless 211A, so net I.B.R. is 584k.

Backstory: this is a church built in the 50's, one radiant floor zone, one convector zone, & one air handler zone. Radiant is directly connected with a manually operated bypass to temper the boiler water, nothing special about the convectors, & there are two air handlers which now operate in parallel with one stat banging the pump on/off (they originally operated independently with 3-way valves to control discharge air temp, but that was knuckleheaded). All the pumps are pumping in to the return of the boiler. There's a decommissioned steam boiler in the mechanical room that's tied in to the same c. 80' chimney. Two combustion air openings that directly communicate with outside.

I'm thinking that I should get (interlocked!) dampers on the combustion air and close off the draft hood & add a barometric & flue damper (again properly interlocked). There's a lot of remediation that could be done to the NBP, but as near as I can tell that will effect comfort levels & reliability, but not so much efficiency. Am I wrong? I'd rather like to have the radiant loop set up as injection pumped & get the 3-way valves back in the air handlers, but that's going to be a lot of expense for not much gains (no complaints ATM!)

Any suggestions? Things I haven't thought through enough or am misunderstanding?


  • pecmsg
    pecmsg Member Posts: 4,952
    1st and foremost..........................Find and Fix the leaks! Keeping the heat in requires less fuel burned.

    Heat pumps for mild times. Big investment but good return on investment.

    Just so much you can do with the boiler unless the funds are there to replace and rework the system.
  • captainco
    captainco Member Posts: 796
    Taking a few measurements would be helpful in determining if what you want to do will be effective. Equipment with barometrics can be tuned better because you are controlling both air and fuel. Draft readings are hepful to determine off cycle losses.
  • ratio
    ratio Member Posts: 3,696
    Exterior storms are on the list to look at, other than that not terribly leaky that I can tell. IDK if I can justify heat pumps.

    Draft is substantial. When I open the chimney cleanout I gotta hold on to my hat. I was planning on starting another thread on the implications of closing off the draft hood—I'm reasonably certain that I'll have to make the argument to the boiler inspector. There is the abandoned steamer that's still tied in to the flue, but even before that the flue off the Peerless is IIRC ±14", & the boiler room isn't hot.

  • pecmsg
    pecmsg Member Posts: 4,952
    Storm windows with a dead air space can make a huge difference.
  • Jamie Hall
    Jamie Hall Member Posts: 23,635
    As @pecmsg said, your biggest bang for the buck is going to be reducing your heat losses. Which is much easier said than done in older buildings.

    Exterior storms should very much be on the agenda -- for two reasons. First, and obvious, they reduce heat loss through the windows, second, and perhaps less obvious but, unhappily, increasingly necessary, is that they help protect the main windows from damage. Not that serious with ordinary glass, but if you are looking at stained glass windows (you mention a church) they are becoming increasingly necessary. And I'd suggest Lexan, rather than glass or plexiglass. More expensive, but much harder to break.

    Check around the windows as well; it is not unusual (particularly in masonry) for there to be some rather spectacular draughts around the outside of the frames.

    You mention the building was constructed in the '50s, by which I assume you mean the 1950s. Was it insulated? If not, can it be insulated or insulated better? That would be worth the effort.

    You may run into some arguments on the draught hood. However, as @captainco says, you can get much better control if you can get rid of it. That doesn't attack the problem of the stack draught on the space, though -- a barometric damper will be wide open on colder days. That said, you may want to consider ways of separating the effect of the stack draught from the rest of the building. You mention combustion air, but I would also consider air sealing the entire mechanical room from the rest of the building, and supplying outside air to it in addition to the combustion air. The only downside to that is the threat of freezing in that space, but that could be mitigated by providing just enough extra heat in that space.

    I doubt that you'll be able to do that much on the actual heating side. It's unlikely that the overall efficiency of the heating system is much less than 80% as is, and even going to much hgiher efficiency boilers and other tweaks I can't see you getting much over 90%. Significant, but not going to make that much of a dent in the gas bill.

    Heat pumps are the current wonder weapon, of course. However, unless you have ducting for air conditioning already installed, you'd be trying to heat the place with air to water, and it's unlikely that that would work with your system. Furthermore, the return on investment is likely to be very small, if not negative -- and you may have trouble selling that if the owners are at all financially sophisticated. If you do have A/C, though, and the air conditioners are due for replacement, installing heat pumps instead might be a very smart move.
    Br. Jamie, osb
    Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
  • lkstdl
    lkstdl Member Posts: 41
    What's your heat load? How much of the year could you run with a lower SWT? With 2-3 residential 199K mod-cons you could seal off the whole chimney.
    Luke Stodola