Diaphragm expansion tank location on American Standard ng boiler

[driger]

No professional would even take on your job without 1st doing a complete manual J heat loss calculation followed most likely by a recommendation that the amount of heat emitters ( radiators, fin tube, convectors) be increased in order to assure that the new boiler can modulate properly and achieve condensing temperatures. Otherwise he would do exactly what you are about to do and then have to put up with your constant phone calls when the system doesn't meet your expectations. From what I've read here already, if you want to do the job right and actually save some money on your energy costs, doing this yourself is going to be disastrous, but I'm betting you aren't going to take the advice anyway.

the problem is you really haven't given any advice other than to go write a blank check to a bunch of ripoff artists.

 

[Tom Sawyer]

Fair enough.

Do a manual j heat loss calculation

Do an evaluation of the existing radiation, zoning, pipe size and flow rates

Do a cost comparison between full condensing and high efficiency non condensing complete with projected fuel use and costs as well as 5 and 10 year amortization of the equipment/installation cost and projected fuel costs for the same period

Determine the best control strategy that will combine comfort with efficiency. Here I'm talking about thermostats, programmable aqua stats variable speed load matched pumping.

Shall I continue? I'm guessing probably not because you consider everyone too be a rip off artist so I guess I'm saying have a nice day, good luck with your project.

 

[Sponsor]

 

[Dana]

90' @ about 580btu per lineal foot @ 180 degree water temperature. So your radiated load is about 47,000 but/hr if your old boiler won't keep up with the heat loss neither will the new one regardless of how big a unit you install. and worse yet, it will NEVER run at or even near the efficiencies that it is possible of achieving. Essentially you are throwing your money away.

That's about the size of it. You can't pump 90,000 BTU/hr into fin-tube that's only capable of emitting 1/2 to 2/3 that. If it's not keeping the house warm it's a radiation sizing/load-matching problem, not an issue with the boiler being undersized. And of course, with low mass radiation like fin-tube it's going to cycle like crazy to no good end.

The smallest-of-that line Sentinal SE-70 has an output of nearly 60,000 BTU/hr which is still ever so slightly oversized for the radiation, but would cycle substantially less. With the SE-70 you're looking at 58,000 BTU for 90' of fin tube, which is 644 BTU/foot, which means you could actually get it to balance at an average water temp of ~190-200F, a feat that simply isn't possible with the SE-105. With the -105 you're looking at 87,000BTU/90' for 967 BTU/foot- you can't get that to balance even at steam-heating tempertures. That's why the -105 is totally a mistake here (like it is in most homes), and a smaller boiler would be a far better choice. Even if it's still oversized for the heat load, as long as it's not oversized for the radiation it won't short-cycle itself into low efficiency and an early grave (unless you micro-zone the place or something.)

An un-insulated air-leaky basement in a cold climate typically represents 15-25,000 BTU/hr of heat load. Sealing up all the big air leaks and putting at least R12 of fire-rated rigid foam (Thermax) on the upper half of the foundation (down to a couple feet below grade everywhere) would be cost effective, and probably fix the comfort issues. The band joist & foundation sill crackage leaks typically add up to more than all of the window & door air leaks combined, and a square foot of R1 uninsulated above-grade foundation wall loses about the same amount of heat than 10 square feet of 2x4 framed wall insulated with R11 batts. Depending on just where you are in ID it might even be worth going with 2" of rigid EPS trapped to the concrete for dew-point control on a non-structural batt- insulated (without vapor barriers) studwall, which would reduce the heat loss out of the basement down by about 95%. But air-sealing is the key first step prior to insulating.

Air-sealing the basement, AND the attic floor plane are the two most critical locations (and any flue/electrical/plumbing chases that run from basement to attic), since the distance between lowest and highest air leak points are what defines the stack pressures, driving 24/365 air-infiltration. Fix those and the air leaks that happen in-between drop an order of magnitude in importance. Fix big leaks first, worry about the tiny stuff later. The band joist/foundation sill is the most commonly overlooked big leak- it's far bigger than you might think.

 

[Tom Sawyer]

You know Dana I think that what bothers me most are those folks that think everyone in the trade is out there to rip people off.

 

[Dana]

You know Dana I think that what bothers me most are those folks that think everyone in the trade is out there to rip people off.

Words to live by:

Do not ascribe malice to that which could be explained by incompetence.

I'm not in the HVAC trade, but have been on both ends of the contracting stick. The average competence level I see out there is a bit wanting- it's at least 5 hacks per semi-competent HVAC contractor (if not worse). I very rarely hack away on heating systems, but when in the market I'll specify the design parameters fairly well, and take responsibility for the design if for some reason it doesn't work out. (Hasn't happened yet, not that it can't. )

It's not hard for the DIYer or homeowner to do some napkin-math sanity checking. It's amazing how many boiler-swappers skip even the most rudimentary math when picking a boiler. (Take the contractor who did the original system here, for instance!) Avoiding oversizing to the point of guaranteed short-cycling does not take rocket science level math or even 8th grade algebra. A 5th grader with ADHD could get there with some coaching.

Even among those who measure-up the radiation rarely analyze the total heat load to see if the boiler could be even further downsized for higher efficiency & comfort, but time is money, and if the client doesn't understand or care, it's not necessarily time well spent for the contractor bidding the project, especially if the competing bidders pick larger boilers. To the typical client bigger sounds better, right? "I don't want to be COLD!" But explaining the nuances to the client takes even more time. It's easy to see how some contractors will burn out, and won't bother putting in even another 15 minutes if it doesn't increase their odds of getting the contract.

I'm sure there are rip-off artists out there, but it's the exception more than the rule. But it's more than just a plumbing job, and taking a handyman wrench-twister approach to boiler or system upgrades isn't likely to yield optimal results. Like a lot of HVAC hacks it looks like driger just picked a boiler in the same approximate size range but a hair bigger since "...the old boiler barely kept the house warm".

I'm not sure what the math was behind, "according to my calculation it's 20% oversized. if go with one a size smaller it's 20% undersized." If it was a heat load calc indicating a design load of 70,000 BTU/hr or something the calculation has to be off by a mile, since the radiation can only deliver about 2/3 that. The system may be under-radiated for the load for the house in it's present condition, but not by fully a third or it would be downright freezing during cold snaps rather than barely-warm.

I hope he hasn't already un-packed the boiler, and can take the advice to return it for a smaller one. It's cheaper & more effective to bump up the radiation in rooms that run cold and/or fix the low-hanging fruit on the building's thermal performance than replace an old oversized boiler with a newer oversized boiler that will deliver exactly the same amount of heat as the old one, no matter what the burner size or nameplate efficiency. Just about anybody's 3-plate cast iron gas burner would cover the actual load if the 90' of fin tube was sort-of keeping up.