Choosing a reliable boiler

[brucewayne]

i figured out the water load nvm, double post*

http://contractingbusiness.com/residential-hvac/how-calculate-water-system-btu-measurements

 

[brucewayne]

i found out via https://www.manualslib.com/manual/834596/Nti-Trinity-Tx51.html?page=7#manual

says "In US/Canada, PVC vent pipe and fittings shall not be used within the closet or alcove; only
approved CPVC, Polypropylene or Stainless Steel vent pipe and fittings can be used"



also page 16
ULC S636 PVC is approved for flue gas temperatures up to 149 F (65 C)
and must only be used for low temperature
applications.

High temperature applications requiring boiler supply water temperatures greater than 140 F (60 C)
use ULC S636 CPVC, Polypropylene or Stainless Steel

 

[Sponsor]

 

[Dana]

CPVC is the most commonly used vent material for condensing boilers in my area. Other types of PVC are not allowed as vent piping when routed up a chimney chase, but CPVC is fine.

A standalone gas hot water heater typically has a 32,000-45,000 BTU (input) burner. Even the smaller condensing gas boilers have higher burner output. With indirect fired water there is no need to increase the boiler size, but for smaller boilers it's best to operate the indirect as the "priority zone", which suppresses the zone calls from space heating thermostats until the tank's aquastat is satisfied. (Being able to assign priority to a zone is a standard feature on nearly all modern zone controllers. ) The recovery time of a 50 gallon tank from a totally-tepid 30C up to fully scald-worthy 55C with 40,0o0 BTU/hr of heat coming from the boiler is about 28 minutes. Most houses won't fall very much in temperature in that short of time even at -20C outdoor temperatures.

A single standard flow shower takes about 75,000 BTU/hr in the middle of winter, but it's only used in bursts of 0.1-0.2 hours at time, which is why you store the heat in a tank, or why you need a really HUGE burner on a tankless hot water heater. You need to cover other hot water draws that might occur when somebody is in the shower to avoid the screaming match. Filling tubs from a tank will be an instantaneous load more than 100,000 BTU/hr, often over 150,000 BTU/hr, but it's only for a short period of time.

 

[brucewayne]

yea only problem its extremely rough math, because need to find the Feet of Pipe from boiler to farthest heating device. only two ways they coulda done it, but anyway.

im sure it will be fine. If washing machine on, everyone used to not taking shower. Plus the city cant pump the water any stronger. Even if i could pump hot water everywhere in house, pump isnt good enough from city side.

 

[edvinpaus]

Hi guys, are you familiar with combi boilers? The combination or ‘combi’ boiler takes its name from its dual function: it’s a high-efficiency water heater and a central heating boiler combined in one compact unit. They provide heating and hot water directly from the boiler, which means almost immediate hot water. In Europe these are the best and most energy efficient boiler manufacturers: Vaillant, Ideal and Worcester boilers.

 

[Dana]

Most combis are either ridiculously oversized for the space heating load or pathetically undersized for the water heating load for typical North American heating & hot water loads. Those with a large thermal buffering water volume are better suited to most homes than the wall-hung combis.

 

[edvinpaus]

What about the Vaillant EcoTEC Plus 831 Combi boiler? Which is suited to 3 or 4 bedroom properties that have one or two bathrooms. In size it's just a regular boiler. Also the Ideal Logic Plus 30kw Combi boiler is well suited for the same size homes, but maybe 34kw would be better suited for the American size.

 

[Dana]

The max 38kw of the EcoTEC Plus 831 is not enough to support the domestic hot water flow requirements of most 2 bathroom homes in the US, particularly in cooler climates where incoming water temperatures can dip to 2C in winter. A single 2.5 gallons per minute shower takes about 25kw in those locations, thus two simultaneous showers cannot make it without a tank/cylinder. Most North American homes north of the 38th parallel will have something between (180-200,000 BTU/hr=) ~50-60kw just for the water heating, unless it has a volume of hot water storage capacity.

Newer-tighter US homes will have 99th percentile design heat loads between 7-12kw, but some older uninsulated homes can hit 30kw or higher.

The modulation range of the burners are not infinite, and the 50kw boiler needed for the hot water may not be able to modulate low enough to run the low-mass radiation at an efficient condensing temperature in homes with design loads less than 15kw without short-cycling into low efficiency and shortened lifespan, especially homes with heating systems broken up into 2-6 smaller zones, each operating independently.

I live in Massachusetts, and at one time the hot water heater in my house was a ~30kw-output tankless. Bathtubs took a long time to fill in winter, and if someone started a load of laundry or filled a washbasin with hot water while someone else was in the shower there was hell to pay, and it was impossible for both the upstairs and down stairs baths to draw adequate hot water at the same time even in summer. A 38kw combi boiler wouldn't cut it either, and the hot water needs at my house are modest compared to most US homes. A 55-60kw combi boiler could handle our hot water loads, but it would short cycle on heating zone calls unless the heating system had a buffering thermal mass of water storage.