Looking for recomendation for a brand and model line for a boiler and Indirect water

[BillTheEngineer]

I am in the process of purchasing a home and I know that the existing water heater is leaking or about to start leaking and the boiler does not look like it is im much better shape. Since the home has gas I was thinking of getting modcon boiler (similar to an instant hot water heater) and an indirect hot water heater. I know I want a stainless steel IWH with a lifetime warrenty. I also know a heat load calc needs to be done and I will most likely do it myself ( I am a mechanical engineer, I will two it at least two different ways to make sure my numbers seem correct). I also plan on doing the install myself.

With some educated guessing I think a 40K to 50K btu /h boiler will be sufficient. The house is a 2200 sq ft high ranch from the 60's. it has replacement windows and vinyl siding. Baseboad heat. there are 2 heating zones. location is long island new york.

Since I plan on saving money by doing the install myself I don't mind spending a little more on a quality system. I am looking for some recommendations one manufatures and what models to look into and what to stay away from. Does it make sense to get a tanka nd boiler from the same mfg? or is this not much of an issue? I have been reading through the install manuals from different mfg's and sometime it looks like it may make it easier installwise to stick with one mfg.

Thanks in advance.

[jadnashua]

Doesn't really matter about keeping the IWH and boiler from the same company. Typically, at least from what I've seen, the temperature sensor for the indirect is part of the boiler's installation kit and all IWH have a well for the sensor. I've got a SuperStor Ultra that serves my needs.

I've got a Buderus unit that I like. I bought it on recommendation from the local installer who had one in his own home plus, the USA distributor is about 15-miles from my house, so expertise and parts are close, if needed.

[Tom Sawyer]

2 votes for Buderus

[Dana]

Competent local support is more important than the manufacturer's nameplate.

Spending the money on a competent hydronic system design to get the most out of it as a system is more important than the boiler. It's more than just an exercise in plumbing. I'm sure a mech-E could become a "Jr. Hydronic Designer" with some study, but it's easy to both under & over design the system. You can burn a lot of electricity to no good end with oversized pumps, but it may not be worth spending money on some of the rilly-kewl toys like ECM drive pumps with programmable delta-Ts, etc. for a 2-zone fin-tube baseboard system.

It's unlikely that you'd be over 50K for a design temp heat load for a 2200' 1960s vintage ranch house if the replacement windows are decent, and it isn't leaking tons of air. But it's always worth reaping all of the low-hanging fruit on building upgrades before (re) designing the heating system. Saving 25% in fuel cost via upgrading the building envelope provides more comfort than achieving the same savings with higher efficiency mechanical systems. In some instances the increased building performance allows you to downsize the boiler, and in all mod-con systems it allows you to run a lower temp reset curve, for higher condensing efficiency without adding more radiation.

The attic usually provides the easiest envelope upgrade for best bang/buck. If there's room to take the attic-R up to R50 with blown cellulose it's worth it. If it has a full basement (or crawlspace), the basement is usually the second-best bang/buck in retrofit improvements. Foam-sealing the band joist/foundation sill and insulating from the band joist to the floor with R10 or better has good return on comfort, if a longer term return (but still a pretty good return) on fuel savings.

If the windows are double-hung clear-glass U0.5 type windows, it may be worth putting low-E storms over all but the south-facing windows to lower the overall heat load and increase comfort both winter & summer. A hard-coat low-E storm over a cheap U0.40-0.60 double-pane brings the U-factor down to 0.28-0.30- better performance than pricier replacement windows, and better than current code-max. If you have a typical 15% window/floor area ratio that's 330' of window. At an outdoor temp of 15F interior of 70F (55F delta-T), with U0.50 windows the window loss is 9075 BTU/hr., but if upgraded to 0.28 performance with low-E storms that's reduced to ~5100BTU/hr, which is likely to be about a 10% reduction in the total heat load. (And you'll never get window condensation, and you won't feel as cold standing next to the window on a winter night.)

Run the heat load calculations only on the "after" picture of any envelope upgrades, but even the "before" picture is likely to be under 50KBTU/hr unless it's practically a "well insulted wind tunnel" on air leakage. It wouldn't surprise me if the "after" picture was under 30K @ +15F (the typical 99th percentile outside design temperature for most Long Island locations. )

Seal up any unused flues, since they would only serve to depressurize the boiler room, driving air infiltration 24/365.

[BillTheEngineer]

Thanks for all the information. I am aware that a competent HVAC designer/engineer would probably be more adept at sizing/designing a system and selecting equipment. But as I read to many posts from other, many installers just pulling numbers out of air and recommending equipment that they routinely deal with. Being an engineer, I always like to do my homework and research first and rarely just go on someone else's word (doctor/lawyer/tradesman/etc). Generally I can figure out if someone has taken a shortcut or missed something (I routinely have had to do this in figuring out why products fail or don't work as expected).

My plan is come up with a system (either equipment list or equipment requirements) and then get quotes from installers and then make a decision on whether I feel like taking on the install myself. I must say that most equipment manufactures are pretty helpful and their install manuals are pretty good (compared to a lot of other equipment I have had to deal with).

I like to be a very well informed consumer, and I know this can be irritating to some. But it's my money, I will spend as I feel, is what it boils down to. I completely agree with getting equipment that has good support and parts are readily available. But I also like equipment that is reliable and does not need constant attention. And I know it all starts with a heat loss analysis. Having access to an IR camera comes in handy in finding and fixing the heat loss areas. My general idea is that most equipment is good (there are always exceptions), what usually leads to a poor opinion of it is poor installation or poor maintenance or improper use.

[Dana]

Yep, enginerds who can do the math are the bane of the HVAC pros, even some of the new-schoolers. ;-)

If you're not going to re-zone the thing or add radiation, measure up the total baseboard length (and type) as that affects both pumping power requirements and determines the low-output temperature at which the even at minimum-modulation the boiler would start short-cycling. If it's really all out of whack with one zone much larger than the other one part of a re-design might be to combing zones or re-configure to allow a lower operating temp without short-cycles. Specifying pumps for a mod-con isn't as straightforward as for low-head cast iron beasts, but it's still mostly the head of the radiation and the flow rate(s) and delta-Ts required/tolerated by the boiler that makes up most of it- both the the boiler choice and radiation type/length count.

The min-output of a mod-con is really the more important number in your system, since I'm pretty confident that the whole house heat load is well within the bounds of the max-mod output of even the smallest units out there (or if not, could be made that low with some judicious envelope upgrades.) The lower the min-output, the longer the burns and the lower you can run the temp for maximum condensing efficiency when loads are low. Going too large can lock you out of mid-90s efficiency if you have a stubby zone unless you start adding radiation (or thermal mass.) So when comparing boilers, keep your eye more on the low-fire input/output numbers than the max, and avoid any temptation to up-size if the heat load calc says it's close- the smallest of the line is your goal.

There's a range of opinions out there, but most-mod-cons are pretty good these days. The Triangle Tube Solo series is popular for ease of installation despite some (mostly resolved) design issues, most installers have nothing but rave reviews on Buderus & Weil-McLain, but it's a moving target- there are others.

BTW: In the 1990s I worked on a few aspects of IR-imaging camera designs as a consultant to Infra-Metrics, before they were acquired by FLIR. Many is the time wished I had some of those toys at my disposal!

[BadgerBoilerMN]

What Dana said, but note that finding modcon boiler before you have an accurate heat load is a waste of time. Moreover, I would want to know the zone loads and available fin-tube for each before deciding on a boiler. Indirect water heaters don't care how they get warm but controls are not always compatible.

While your saving all that money, get a little professional e.g. experienced help. You'll be glad you did.