Measuring heat loss for a properly sized Combi
I wish I had the room for a boiler and an indirect but utility closet is like 3X4
Current Combi Boiler is 175K. (Grossly oversized)
Currently there is roughly 100 feet of slant finn baseboard(The 3inch deep by 3 or 4 inches high. I think it's the smallest they used to make) over two zones. If I take this 100 X.0500 I get roughly 50K.
Also on this boiler would be 1 shower (no tubs) and a 1/2 Bath and a 1 dishwasher
Would a 60K(for heat) and 160K for hot water combi work. (3.3 GPM which I think is more than enough)
I've had three plumbing and heating guys come in and say they would go bigger and put in a 199K. I don't see the reasoning behind this. Any guidance is appreciated.
btw not one did a heat loss calculation.
Comments
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Is the 160kbtu for 3.3 gpm at your incoming water temp?
The heating part is sized by doing a heat loss calculation on the part of the building to be heated but with a combi it probably is going to be the DHW that will tell you what boiler size you need. DHW is usually set up as a priority over domestic heating so it only needs to meet the DHW need, not both combined. Keep in mind you need the output, not the input to the boiler.
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Can you build an attached shed outside the house for a boiler and indirect?
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab1 -
140kbtu or even 120kbtu would be fine too, depending on the shower head. A heat loss isn’t needed here, it’ll be oversized no matter what. Use the turndown to help with shortcycling.
Other option would be a boiler that’s a storage tank - so like indirect + boiler all in one.
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The coldest incoming water temperature is the key to all this. It can be as low as 35F in cold climate, as high as 90 in southern cities.
Well water tends to be around 50- 55 year around.
With those numbers you size the DHW btu required.
With a combi, the dhw load will be bigger, much bigger.
50,000 btu/hr of fin tube output? That is probably at 180F. A heat load calc would determine how often you could run cooler, more efficient SWT.
Our family of 2 gets by with a 120K combi on well water temperatures. A 120K combi turns down to 12K, so the heat load will be easy to accomodate.
Most tankless size be 70- 77 degree temperature rise. So if you want 120F at the fixtures use these numbers to get your gpm. 2- 3 gpm can work for many folks.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream1 -
Hi Alan - Definitely out of the Question.
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@Hot_water_fan I thought of that. I know of 2 I believe. The Laars FT Floor Standing has a small indirect ,that is only available in the 199K BTU (Min BTS 20K) and the Viessmann 222-F. The Viessmann 222F is a nice looking boiler.
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I just installed a Burnhma Alta 136 combi on home that has 11/2 baths. I installed a mixing valve on the domestic side which is required by most boiler manufacturers which make combi boilers. I set the dwh to 140 and mixed down to 120, have had no issues with be able to supply enough hot water.
I personally am not a fan of combi boilers but space was limited.
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Anyone ever install a cast iron boiler + 30 Gallon indirect in a 3X3X8 foot closet?
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I haven’t especially the way I plumb boilers. @Le John where are you located?
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NTI has a 20 gallon, wall-hung indirect that would easily satisfy your DHW needs. It comes with a tempering valve.
8.33 lbs./gal. x 60 min./hr. x 20°ΔT = 10,000 BTU's/hour
Two btu per sq ft for degree difference for a slab
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I replaced 16year old Laars Mascot combi, actually a Baxi, 133K I think, with a Lochinvar Nobel110. Bothe kept up with a shower and any other small draw, like a hand sink, .35- .50 gpm, or a dishwasher fill. I also had a Lochinvar combi at the main house.
I like Lochinvar, I have had the most experience with that brand and the control settings are easy for me. Great support if you need it from reps or tech support. From my experience.
In my current shop I have a solar tank with a small plate flor DHW, my outdoor shower.
Or I added a plate to a Lochinvar 55K for winter use. It keeps up with a hose for squirting off the truck salt grime. Basically a homemade combi without a need fopr a diverting valve or OEM HX block inside. A pump, plate HX and .35 flow switch is all it takes. Connected to DHW demand so the boiler high fires for DHW.
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream0 -
It's not cast iron, it's steel and better than any cast iron boiler. Energy Kinetics makes a version of the System 2000 that has the boiler above a small storage tank. With their plate heat exchanger it produces plenty of hot water. With the Carlin EZ gas burner you will get over 85% AFUE and you don't have to deal any condensate or modulating equipment, much more appropriate for baseboard heating than a combi in my opinion. I've seen these boilers fit in tight closets nicely.
EK also has the Resolute boiler that is designed to replace tankless coil boilers, although I am not sure if they are available with the Carlin EZ gas burner, I've only seen them with oil burners.
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Thanks @SuperTech! All of our non-condensing boilers are fuel neutral and will operate on oil, Nat. gas or propane with a Carlin EZ gas burner.
@Le John - Take a look at our System 2000 stackable or Ascent Combi they maybe an option
Questions feel free to reach out
Jay
Jay McCay
National Sales Manager
Energy Kinetics
908 328-7154 cell0 -
Hi Jay - I don't believe any of the units will fit in a 34 inch by 34 inch closet. When I look at the diagram I see that I need 49 inches from from to back with the burner door open.
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@Le John , the footprint for the EK1 model (up to 140,000 BTU/hr) is 29 ¼” wide by 30 ½” deep with the service door closed. You can usually open the swing down service door (like an oven door) through the closet door, so the open door is not usually an issue unless the doorway is less than about 24” wide. You indicated 175,000 BTU/hr is grossly oversized so maybe the EK1 is adequate (you’ll have hot water storage so you won’t need the firepower for instantaneous hot water). As a reference, the EK1 is sized properly for applications with consumption up to 2,800 therms of natural gas per year.
Robert W.
Energy Kinetics
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My mistake, I got the EK Ascent and Resolute mixed up.
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