Hydronic system design

keegs

I'm designing a hydronic (central) heating system for a two story seasonal residence in climate zone 6. The house is approx 8 years old. It's 2x4 construction w/R13 insulation in the walls and R35 in the attic. It has double pane vinyl windows and steel insulated doors. There's a full uninsulated basement.

There's a 2 flue, 6" tile, masonry chimney with a thimble that services a 65k BTU coal stove on the main floor and another thimble in the basement that's not currently in use.

I plan to use a New Yorker 90k BTU hand fed coal boiler as the primary heat source in the basement with propylene glycol in the system.

During construction I ran 1/2 pex tubing from the basement to the floor joists under the second floor bathroom and to locations in each of the two bedrooms from which I plan to install baseboards.

I plan to install baseboards and under floor heating from the basement for the main floor.

The basement, first and second floors each measure approx 400 sq/ft. The basement and first floor ceiling heights are 8' and the second floor ceiling height is 7.5'.

One second floor bedroom has three double pane windows (measuring approx. 24w" x 44h" . The bathroom has a 18" x 24" double pane window and the second bedroom has one 24" x 44" inch window.

The main floor has a 32" w steel insulated door with double pane window and a 36" w steel insulated door. A storm door is installed on the larger exterior door. The main floor has four 24w x 44h windows and a 36" wide by 32" h window. An uninsulated solid wood door provides access from the first floor to the uninsulated basement.


Questions that I'm noodling:

How much 3/4" copper fin tube baseboard do I need on the second floor?
How much 3/4" copper fin tube baseboard do I need on the first floor.
How much underfloor radiant tubing do I need to run in the first floor joist bays?
Will the radiation capacity of the system accommodate exceeding high temperature boiler water/glycol limits particularly in the event of a power outage?

Thank you in advance for any help you may offer.

Jamie Hall

Heat loss calculation. It's been said many times, but before you go any farther at all you must do a room by room heat loss calculation on the structure. Slant/Fin, among others, has a very good heat loss application which can either run on a smart phone or on a computer. Easy to use, reasonably accurate results.

Do it.

Then you have a chance of being able to size your fin tube and radiant realistically; anything else is a WAG.

In answer to your high temperature question, the answer is no. You need to provide some sort of heat dump capability independent of the built in radiation.

Jolly Bodger

In addition to doing a Heat Loss Calculation, Uponor has a very good PEX design manual that covers all the instillation options and gives you all the calculation information inclusion flow and head loss. I ordered a hard copy so I could bookmark pages and highlight tables.

Ironman

A heat loss calculation is the first step and the foundation for designing everything.

You may wanna consider a propane boiler instead of coal. Coal isn't as economical as most people think when all factors are considered. Every house I've seen where one was used was a filthy mess from the coal dust.

A mod/con would not only be economical but could could also be set to maintain a very low minimum temp without damaging the boiler.

Glycol would protect the hydronic lines, but what about your potable lines? If you use a mod/con, you wouldn't have to be as concerned since they have a freeze protection mode.

keegs

Thanks all.

The Heat loss calculation for the main plus the second floor is approximately 50k BTUs.
I’m not considering an alternative fuel.
This will be a single zone system with four loops.

My understanding is that the dump zone capacity should equal approx 10% of the boiler capacity which equals approx 9k BTU under a full load of fuel, perhaps somewhat less since the boiler is approx 75% efficient. The dump zone must be located above the boiler.

What are some options for radiating off the excess heat in the event of a power failure?

Jolly Bodger

Run your heat calc per room to get your BB and radiant sizing per room.
As for the dump zone. I would plump a gravity system to the first floor, nice old cast rad, and zone it with a NO (powered closed) zone valve. In the event of power failure the zone valve will open and let the gravity zone dump heat. Could just plumb all your zones (except radiant) for gravity and relay the zone valves to reverse act the heat signal.

KC_Jones

keegs said:

The basement, first and second floors each measure approx 400 sq/ft. The basement and first floor ceiling heights are 8' and the second floor ceiling height is 7.5'.

keegs said:

The Heat loss calculation for the main plus the second floor is approximately 50k BTUs.
I’m not considering an alternative fuel.
This will be a single zone system with four loops.

Are you sure about all that? How did you accomplish the heat loss calculation?

If I am reading this correctly you have a total of 1200 sq ft and only heating 800 sq ft, if that is correct there is no way your heat loss is 50k, I'd be surprised if it was half that.

I will reiterate the answers to your questions are a room by room heat loss calculation.

keegs

Thanks KC...maybe heat loss is the wrong term? I arrived at 50k using the slant fin calculator as suggested in an earlier post.

KC_Jones

I'd be very curious what design conditions you used to get that high. That's 62 btu per sq ft. I live in a 100 year old house, virtually no insulation, original single pane windows and sitting right around 38 btu sq ft in climate zone 5. You should be lower than me with modern construction like you have.

keegs

Jolly Bodger said:

Run your heat calc per room to get your BB and radiant sizing per room.
As for the dump zone. I would plump a gravity system to the first floor, nice old cast rad, and zone it with a NO (powered closed) zone valve. In the event of power failure the zone valve will open and let the gravity zone dump heat. Could just plumb all your zones (except radiant) for gravity and relay the zone valves to reverse act the heat signal.

Thanks Jolly,

The slant fin app gave me the fin tube lengths for each floor......w/out adding into the mix the under floor radiant. Thought about using cast iron radiators and I may still if necessary but the baseboards take up less space and it is a wee house.
Ideally I’d like to design the system to dump to the first floor baseboards. Based on the calculation it’s almost a foot of bb per 1k BTU required to heat the space. So if I understand you, I could make the first floor baseboards a separate zone and use it to dump to.

keegs

KC_Jones said:

I'd be very curious what design conditions you used to get that high. That's 62 btu per sq ft. I live in a 100 year old house, virtually no insulation, original single pane windows and sitting right around 38 btu sq ft in climate zone 5. You should be lower than me with modern construction like you have.

I’ll run it again KC. I’m in zone 6. Northern Maine.

Henry

Using our gas utility standard in Montreal, your actual load is around 33,600 BTU.

Solid_Fuel_Man

Where abouts in Northen Maine? Aroostook county is zone 7.

keegs

Solid_Fuel_Man said:

Where abouts in Northen Maine? Aroostook county is zone 7.

Bridgewater ....

keegs

The fin tube calculator and two other online calculators indicate the BTU requirement is approx. 50k BTUs. You guys want me to make something up?

Jamie Hall

No, we certainly don't want you to make something up, and I can see the possibility of 50,000 BTUh as a load. We just want to make sure that your numbers are right, since it can be so disappointing if they aren't...

If you used Slant/Fin's calculator, did you also record the room by room heat loss? I see that you did get the fin tube length for each room. If you also have the BTUh requirement, you can also figure what size cast iron radiators you would need instead. There's a chart for that somewhere, which relates the output in BTUh to the EDR for the radiator for various hot water temperatures. Very roughly (but probably close enough) you can get the heat output by subtracting 70 from your average water temperature and dividing that into 140 and multiplying the result by 240.

Jolly Bodger

@keegs , Yes you can set up the first floor as a zone and set it up for dump. BB will be a little more difficult to do this with vs a cast rad.
Something seems off, 1K per foot? I don't think they are rated for that. If I remember correctly they are 550BTUH per foot at 180 degrees.
Maybe there is a conversion factor throwing off the math?

KC_Jones

What design conditions are you inputing into the app?

Just to confirm you are talking about 800 sq ft of heated space?

I input into the app as if you had 400 sq ft room with 12 windows and an outside design temp of 0 and got 7900 btu. I got it to 25000 by using an outside temp of -160.

This is why I question the results you are getting.

keegs

Jolly Bodger said:

@keegs , Yes you can set up the first floor as a zone and set it up for dump. BB will be a little more difficult to do this with vs a cast rad.
Something seems off, 1K per foot? I don't think they are rated for that. If I remember correctly they are 550BTUH per foot at 180 degrees.
Maybe there is a conversion factor throwing off the math?

Thanks.. You're right I was mistaken earlier regarding the BTU / per linear ft. of fin tube.

The first floor is one room, According to the Slant Fin calc. the first floor BTU requirement 25,536. It suggests 3 types of baseboard, two are hot water and they're rated in the 550 - 570 BTU p/ft.

For the dump zone::
I'm not there right now so I'll guess I have 25 ft of exterior wall that can accommodate baseboard. 550 x 25 = 13750 BTU. I would run the baseboards in a series on a separate loop with 3/4" copper. supply and return. A zone valve would control this loop and default to open in a loss of power event.

How am I doing?

To complete the dump zone design I think I need to calculate the BTU /h that the first floor underfloor radiant loops (1/2 " pex) and the second floor loop (1/2" pex) will produce during a loss of power event. Not sure how to do this.

Jamie Hall

There is a fundamental problem here with trying to use baseboard as a dump zone in a power failure situation. The figures you are quoting assume that there is a pumped flow.

How, exactly, do you expect to get that flow with no power available to run a pump? You aren't. Gravity convection will give you some flow -- but not much with the pipe size and head involved.

Unless your coal burner is designed and set up to completely kill the draught on power failure -- the inlet dampers close completely -- you are going to have a problem.

Jolly Bodger

@Jamie Hall is right. Gravity systems used large pipes and 3/4" horizontal BB is not going to flow much. If a cast rad is out of the question you could put the circulator on a UPS. Modern pumps don't draw much. Would need to make sure run time would exceed possible fuel load.

keegs

And we haven't addressed the radiant capacity of the other loops during an outage.. Okay then .. Thanks guys for your attention. A solid fuel boiler may not be appropriate in this instance.

hot_rod

A computer back up would run a low power draw ECM circulator for enough time as long as the boiler is able to shut down. Damper off the air source to the fire for example

Solid_Fuel_Man

I have quite a bit of experience with gravity flow and dump zones. You cannot have much horizontal run, and what horizontal you do have should be sloped a min on 1/4" rise per foot run to get much flow at all.

What coal boiler will you have? EFM or Keystoker? I know what Center Farms charges for a ton as I assume that is where it will come from. Coal really only gets messy with larger boilers and a lot of handling.

I'll PM you with some further ideas. I'm only three towns away.

keegs

Solid_Fuel_Man said:

I have quite a bit of experience with gravity flow and dump zones. You cannot have much horizontal run, and what horizontal you do have should be sloped a min on 1/4" rise per foot run to get much flow at all.



What coal boiler will you have? EFM or Keystoker? I know what Center Farms charges for a ton as I assume that is where it will come from. Coal really only gets messy with larger boilers and a lot of handling.



I'll PM you with some further ideas. I'm only three towns away.

Thanks SFM... I'm looking at a used New Yorker WC-90. It's more boiler than I need but there's not too many used boilers smaller than 90k BTUs out there.

I do get some fuel from Center Farms. But lately I'm trying to catch the sales at TSC. I recently picked up a ton there for $250.

This is a seasonal residence. I heat the place now with a 65k BTU Coal Chubby stove. It does a good enough job but it can take up to 12 hours to get the place comfortable during winter months.

The primary on the WC90 is a small vent on the side of the combustion fan. I don't have experience running this boiler but I can slow burn the Chubby for 8-10 hours with the primary and manual damper completely closed and it only holds about 25 lbs of fuel.

With regard to rise and run, do you mean the fin tube baseboard should be mounted with 1/4" rise per foot of run? The Mrs. would love that It's a tight little house. I don't think radiators would be practical. I'm also not going to get much radiation out of the underfloor when the pumps are off.

There is a full unheated basement though.

Jlinde37

How are you making out with your boiler install? I recently installed an oversized hand fed coal boiler. (ds3200 160k btu rating). have a smallish 1750sq ft house with dual temp system. I have zero overheating problems. I do however have 1/3 firebox reduced netting 106kbtu. My heat load is only approx 45k btu.