New System HELP!!!!!

[mhanley41]

I am debating between two proposals and any insight is helpful.
1) Buderas G115WS/4 with Riello Burner and 40 Gal. Bradford White indirect water heater. Using 3 zone valves for the two zones and the indirect. Spirovent air elimination. Installer is a small 3 man show who also did my BOSCH AC/Heat pump this past spring. Work was quality and efficient.

2) Viessmann VITOROND VR-1-27 92 with Riello Burner and 35 Gal Vaughn indirect water heater. Using 3 circulators for the two zones and the indirect. Honeywell (super??) air elimination. Installer is my oil company with mainly 5 star Google reviews. Cost is $200 less than option 1.

All other work and accompanying parts are on par with each other.
Not sure if there is a wrong choice, but maybe there's a better choice?

Thanks!

 

[WorthFlorida]

I couldn't tell you the difference with these units. To me what is important is the service and support you would get from the two bidders. The company you buy oil from would probably give you the service needed for annual cleaning and any future repairs. The oil company probably been selling the Viessman for a lot of years and they must feel comfortable since they have to back up any warranty work. Oil companies know oil furnaces, HVAC guys most likely do not.
Who would you call at 3:00am on the coldest night when the furnace quits and it is zero degrees outside? You won't call the oil company to service your AC Heat Pump.

 

[Sponsor]

 

[Jadnashua]

Both of those units may be oversized. Without having a good analysis done first, you won't know. Probably the worst thing is to just replace same with same, as way back (and even today) the trend is to oversize the thing, often by a lot. That creates a hit on efficiency and comfort, plus costs more up front to buy.

There are ways to estimate quite closely how large of a unit you require. Do a search. You'll need the amount of oil used with a K factor, and the heating degree days for the period of use. Then, you can calculate how much actual heat was generated to keep your house warm. only then will you know what sized unit you need.

Keep in mind, a unit works best if it actually runs constantly, just holding the home temperature where you requested. That's nearly impossible, but sizing it for the typical 95th percentile day generally is. What would happen then, is on that day when it's beyond the design load, the house might cool off a degree or two until the sun comes up. Having it slightly oversized isn't a huge penalty, but it becomes one once the oversized factor creeps up. For practical reasons, nearly anything you buy is likely to be somewhat oversized...just want to minimize that, and to do that, first, you need to know what's actually required.

Don't size the boiler for the WH unless you're running something like a spa or laundromat where you need a constant, high volume of hot water. Generally, the indirect is on a priority circuit, so it gets the full boiler heat when needed, and then things return to heating the house. In a typical house, you'd never notice.

 

[Dana]

Jadnashua has it right. Either one of those boilers would be more than 2x oversized for the average house in NY, 3x-4x oversized for a lot of houses on L.I. or Westchester, but might be right-sized for 3500-4000' house in the Adirondacks, or a 6500-7000' mansion on L.I.

Bottom line figure out your design heat load before proceeding. This is as much a matter of comfort as it is efficiency or cost.

ASHRAE recommends holding the line at 1.4x oversizing for the heat load at the 99% outside design temperature, which is more comfortable than the 1.7x oversizing assumption in AFUE testing. Most boilers I encounter in-situ are 3x+ oversized, bad for efficiency, bad for comfort.

Do you have enough radiation in the whole house to even emit the full burner output? Measure up your radiation to get a handle on it. Most fin-tube or ~10" tall cast-iron baseboard delivers about 500 BTU/hr at an entering water temperature of 180F, average water temp of ~170F. Cast iron radiators deliver about 170 BTU/hr per square foot equivalent direct radiation under those conditions.

A primer on how to calculate the heat load based on fuel use lives here. The same information can be derived from a wintertime "K-factor" (= base 65F degree-days per gallon), if you were on a regular oil fill up service last year. Shoulder season data it too skewed by solar gains, hot water use, and inefficiencies related to gross oversizing to be very useful- it has to be wintertime fuel use periods, where there was a fairly constant and sizeable heat load that it was serving.

Even if the boiler is of necessity oversized for the whole house heat load (oil burners don't go much smaller than 70,000 BTU/hr, which would be 2x oversized for my house), try to keep it from also being oversized for the radiation. With two zones even the smallest oil boilers are likely to be oversized for the individual zones, but can still do just fine (efficiency wise) with smarter heat purging boiler controls. The VR-1 series boilers can be retrofitted (or purchased with) the Hydrostat 3250 Plus heat purging controller, and Buderus has their own home-grown smart controller to manage it.