90% plus boilers, worth it in this case?
Question: High efficiency (90% plus) vs. lower efficiency (86% or so) gas fired boilers. I’m a remodeler in the twin cities. We’re working on a basement remodel that will get in floor heat, then all the first floor radiators go away and the basement ceiling will be under floor heat for the first floor. The second floor original (1920’s) radiators will remain. Our heating contractor is against the high efficiency boilers: He says- gunk in the original radiatiors will dampen the efficincy of the smaller coil area. Warranty/callback issues, unproven track record. Expense, greater equipment cost, plus higher piping costs b/c of this case where we have to feed higher and lower temps. to radiators vs. in floor, underfloor. Cast iron (86% eff.) are cheaper, more reliable, ready to pipe for this application. What’s the deal how can I sell this to homeowners who want to pay more for more efficiency? Is our heating guy stuck in the past or legit. concerns?
Thanks for any info.
Replies
Welcome Midwest,
You quite possibly have a dinosaur on your hands.
Two types of emmitters means a two temp system no matter the boiler choice.
A mod/con boiler will happily supply the cast iron
Try over at heatinghelp.com lots of good people there.
Cheers
Condensing boilers have been around for a LONG time. The other poster is right ... radiators and radiant floors mean two temps ... regardless ... but that isn't a big deal. One or two 3way valves would take care of that. If the owner wants to do the best, put in a reset controller. In Mpls that would be a good addition as there is substantial swings in the winter temps.
Personally, I'd get opinions from more contractors and grill them for answers to logical questions. I tend to react that your guy is a bit 'old fashioned'. What's wrong with acid washing/refurbishing the old radiators?
More guys will jump in here and give their two cents, too. Don't back off yet. Get educated a little then you can make an informed decision. This is a start.
Cast iron rads are a wonderful heat source. In floor heat is even better! Make sure you insulate the basement floor as much as you can to reduce heating the mud under it.
Sounds like you guy is not up to the job. The system just needs some design work. Correctly zoned and setup to supply the right temp to each area it will feel real cozy in winter.
90% plus units have been around for many years. "Cheap" is what stops people installing them. All replacements should be 90% plus.
Yes, what everybody else said...but what is the first floor situation? Is it existing hardwood floors? Are you planning on a staple up system? What are the first floor wall insulation / window specs? It is very hard to push much heat through a wood subfloor / hardwood floor combination. If the first floor is not very tight and well insulated, staple up radiant will not work very well, even with aluminum transfer plates. Often the system will not run as much during the day due to solar heat gain, but when the sun goes down and the temps start to drop, the floor will take a long time to catch up. I would think long and hard about losing the first floor radiators...I know it is tempting, but a staple up system in the twin cities with our extreme winter temp swings requires a very particular set of conditions to work well. With a heated basement, the floors will always be decently warm, and you can't beat the comfort and responsiveness of the cast iron radiators.
My plumber has been having success with suspended pipe systems and wood floors. The key is to have more insulation under the tubes than above the tubes (in the flooring in other words). Given that wood is only R 1 per inch, that shouldn't be hard. You can also run much hotter water in these systems than conventional radiant.
Not sure about the condensing boiler. I do know that your return temp has to be low enough to condense the water out of the exhaust, or else you are wasting your money. I would call the manufacturer of the boiler or the heating guy at a plumbing supply house that sells that model.
I wouldn't discount what your heating guy says out of hand. 4% efficiency is not much. If he is right and the heat exchanger gets dirty, you're going to lose more than that.
From a simple efficiency standpoint there's not much difference. The HE unit will save about another 5% on the heating bill -- nowhere near the 25-50% savings you often see when trading out a dinosaur for even a modern 86% unit.
One significant consideration is the difference in flues -- in general an 86% unit needs a standard high-temperature flue while a HE unit needs plastic flue piping. There may be reasons why one is desired over the other in a given installation, especially in a retrofit. On the one hand there's the opportunity to abandon and remove a conventional space-occupying flue, but on the other hand you can have problems if there are other appliances (like a water heater) sharing the now-oversized flue.
Edited 3/21/2009 4:55 pm by DanH
I learned after I purchased (no idea why) that my plastic flue water heater was NOT a HE system, but a 85% system. I just assumed the plastic flue meant condensing, high effficiency. Apparently not. Not sure why, either.
Right. I've heard that some (perhaps most) induced draft water heaters are lower efficiency units. They mix air with the flue gasses exiting the heat exchanger to produce a cooler exhaust that can use plastic pipe.
The modern conservative is engaged in one of man's oldest exercises in moral philosophy; that is, the search for a superior moral justification for selfishness. -John Kenneth Galbraith
I have been involved in a many old system upgrade and improvement projects. IF you open up an old system and simply replace a noncondensing boiler with a condensing boiler you will most likely "#### it up". But, if you throw you car in reverse while doing 70 down the highway, you will very likely fry your automatic transmission. Does that mean that auto trans are junk? No, it means if you do stupid things, consequences will follow. Second, a good condensing boiler will be more like 94% AFUE and most non-condensing boilers will be 82% or less AFUE.
Step one - find a new heating contractor. Step two - plan on a flush, clean and passivation step in any system that has iron components, especially black iron piping over 30 years old. (This is a good qualifying question for the replacment heating company - How would you perform this function? IF they have no idea or claim there is no need, keep lookin'!) The correct answer has a couple of versions, but should include a side-stream filter, descaler-degreaser-passivator treatment (usually a single properitary product), a flush 7 fill and some level of permanent/continual treatment. This is minimum acceptable practice in commercial work, "good to best" practice in residential systems.
Find someone that knows system operation, design and controls. 99% of the plumbers that pretend to be heating contractors (i.e. the guy you deal with now) do not fall into this category. To get the most benefits from modulating condensing boilers, you have to understand their best practices, weaknesses and compromises. Retrofits will invariably be compromises.
Cast iron, non-condensing boilers are cheaper. Setup properly, they will last longer than two roofs, or more. Witout any change in the lod system, the rest is true as well. A pretty easy swap. In your environment, a modulating condensing (mod/con)boiler, correctly sized (also another qualifying question for a heating professional - How do correctly select a replacement boiler? If the first sentence in answer to that question does not include the words "load calculation", keep lookin'!), installed and controlled will have a payback of 5 years or less.
Combining indirect domestic hot water to a mod/con boiler upgrade only quickens the payback and sweetens the pie.
I second Tim, but no flush will get everything. Use a dirt separation strategy as well.-------------------------------------
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