The original combi boiler

hot_rod

possibly still available?
So if you have a 1200 sq ft home, 3 zones, 24,000 design day heat load for example and you want 4 gpm DHW, a boiler around 168,000 input is the correct choice.

Turn down to handle a single 8,000 btu/ hr load?

Cycle efficiency at that condition?

mattmia2

You certainly wouldn't get 4gpm of dhw out of that with a tankless in michigan...

hot_rod

that assumes a 77 degree rise, 43- 120 for example
33 degree incoming would be 110 supply, I suppose

ScottSecor

@hot_rod your example (Weil McLain WTGO) was the standard boiler here in my area of NJ for hot water systems that were installed in the 1960's and 1970's. Almost every home built before 1970 was heated with oil, and there was no gas run into the house. Electric rates were likely very high so almost no one used electric water heaters (or the grid was inadequate). I can remember questioning these boilers overall efficiency when I witnessed the short cycling with one small zone calling or someone washing a few dishes in the sink. Talk about short cycling.

Even more popular around here were oil fired steam boilers (cast iron) with tankless coils and no mixing valves. These were the homes built before WWII. Imagine washing your hands when the boiler had a full head of steam? Many of these boilers were fitted with a 1.25gph nozzle (roughly 175,000 input), they also short cycled quite a bit in the 'off' season.

Derheatmeister

hot_rod said:

possibly still available?
So if you have a 1200 sq ft home, 3 zones, 24,000 design day heat load for example and you want 4 gpm DHW, a boiler around 168,000 input is the correct choice.

Turn down to handle a single 8,000 btu/ hr load?

Cycle efficiency at that condition?

I remember seeing the"Gold" series at one of the AHR events becoming even more efficient.
All that was done is to install a exhaust economiser..Yeah baby.
Forget about OutDoorReset and Modulation.Just condense the exhaust gases.