Mod Con boiler supply temps when run with baseboard or radiators

bmwpowere36m3

I'm renovating my home, '56 single-story ranch ~ 1600 sqft, gutted and currently installing drywall. My plumbing supply guy turned me onto a Lochivar Knight Mod Con and Crown DWH... he figured I would need a WHN085 (69 MBH water). The house originally had a oil-fired boiler, HW storage tank, baseboard and crappy insulation

I've ran the heat loss calculations myself using the SlantFin calculator and they agree with what the plumbing supply guy did (~ 62 MBH). My design day temp is 7* F (outside) and 70* F inside. Based on my design day temp, heat loss and available wall space using:

• S/F Line 30 BB, 165* F (average supply temp)
  
• S/F MP 80 BB, 150* F (average supply temp)
  

What average supply temp should I be targeting (baseboard vs. radiators)? I understand the lower the better. For panel radiators the problem comes down to size of radiator and cost.

I was also planning on running multiple loops for different rooms, each with a dedicated thermostat. I don’t know whether having too small of a loop would be a problem. Current the plan is to have the following loops:

1. Living + Kitchen ~ 17.3 MBH
   
2. Master Bedroom ~ 6.2 MBH
   
3. Master Bath ~ 5 MBH
   
4. Bedroom ~ 6.7 MBH
   
5. DWH ~100 MBH (input capacity)
   
6. Entrance Hall + Mudroom + Guest Bath ~ 13 MBH
   

GW

sir/madam, yes, the lower the temp the better. Your plumber can't give you info on how much more radiation you need to get to your desired max boiler temp at design conditions? 180 is the old fashioned target at design temp. The lower you go, the more money you will spend to get the system to operate at those lower temps.

Gordy

A word or two.

Your emitter choice manufactors will usually have outputs per Lin. Ft. At different water temps. Use those numbers to compare to the room, or zones heat loss.

Remember that AWT will only be at design day conditions. From there any warmer OAT will use cooler AWT which will be controlled by your outdoor reset control on the boiler.

Speaking of zones or the want of. Do not over zone! A zone if desired should be above the minimum modulation of the mod/con or else short cycling becomes an issue. You really need to think about your desired temperature habits. Also the design concept of the home. Do you prefer lower sleeping temps etc. your house is only 1600 SF. So if you really think you need to then combine enough zones to meet min modulation. Honestly looking at your btu requirements for rooms your missing some 42k heat loss was 62k?, or the balance is basement 20k seems high for a basement.

Judging from what I see kitchen living room a zone. Master bed master bath a zone, guest bedroom, and bath a zone, entrance hall mud room tied to what ever the other missing 20k is at. Personally I would not bother zoning.

bob eck

Check out the sterling Synergy copper baseboard at www.sterlingbaseboard.com/documents/DL-SG-1.pdf
On design day you could send out 150* or 140* water temp and if you can bring the water temp back below 135* you could keep the boiler condensing most of the heating season. Small zone will not be good for the boiler.

bmwpowere36m3

GW said:

sir/madam, yes, the lower the temp the better. Your plumber can't give you info on how much more radiation you need to get to your desired max boiler temp at design conditions? 180 is the old fashioned target at design temp. The lower you go, the more money you will spend to get the system to operate at those lower temps.

I understand. I gave him a layout of the house and he did a calculation and said I should go with the Knight boiler WHN085 rated at:

BTU Input: 85000
IBR Rating: 69000
DOE Rating: 79000

It will be installed in an unheated basement.

I ran the heat loss calc as well using the SlantFin tool.

bmwpowere36m3

bob eck said:

Check out the sterling Synergy copper baseboard at www.sterlingbaseboard.com/documents/DL-SG-1.pdf
On design day you could send out 150* or 140* water temp and if you can bring the water temp back below 135* you could keep the boiler condensing most of the heating season. Small zone will not be good for the boiler.

I used the SlantFin specs and I can run 165* F or 150*F average supply temp given the wall space I have (depending on if I use the Line 30 or MP 80 baseboard). People mention a 20* delta (supply temp, In vs. Out), but say most baseboard installs you'll be lucky to have 5 or so degrees (unless the room is really cold).

I looked at each individual room as a zone (thinking that's what I wanted to do. If I combined rooms into zones, I would have to know the delta T from room to room… If there is some equation I should use that be great.

Gordy

You said your heatloss is 62k the rooms listed come to 46k where is the 16k that's not in your post going to?

bmwpowere36m3

House layout… I'll get a better pic later



Areas with red lines, I don't plan on putting in emitters and I didn't factor them into the heat loss calcs of the other/surrounding rooms.

The "main" house is 1300 sq ft. The entrance hall, closet, mudroom and bathroom are something I'm planning in the next year or so.

Gordy

I think if I were you I would run your heatloss calc again. There is no way 62k is it. that's almost 39 Btus a SF. You sound as though you renovated insulated?

bmwpowere36m3

Gordy said:

I think if I were you I would run your heatloss calc again. There is no way 62k is it. that's almost 39 Btus a SF. You sound as though you renovated insulated?

I updated the original post and looked over my heat calc again. I get a total of 48 BTUs/hr. Thinking about it again, I don't remember what the plumber supply guy… Design temp also has a significant impact on the #'s and I don't know what he used. I used 7* F and 70* F inside.

2x4 walls, R15 (Tyvek outside/taped and top/bottom plates caulked) and 2x6 ceiling joists, R19 + R30.

bmwpowere36m3

Gordy said:

A word or two.

Your emitter choice manufactors will usually have outputs per Lin. Ft. At different water temps. Use those numbers to compare to the room, or zones heat loss.

Remember that AWT will only be at design day conditions. From there any warmer OAT will use cooler AWT which will be controlled by your outdoor reset control on the boiler.

Speaking of zones or the want of. Do not over zone! A zone if desired should be above the minimum modulation of the mod/con or else short cycling becomes an issue. You really need to think about your desired temperature habits. Also the design concept of the home. Do you prefer lower sleeping temps etc. your house is only 1600 SF. So if you really think you need to then combine enough zones to meet min modulation. Honestly looking at your btu requirements for rooms your missing some 42k heat loss was 62k?, or the balance is basement 20k seems high for a basement.

Judging from what I see kitchen living room a zone. Master bed master bath a zone, guest bedroom, and bath a zone, entrance hall mud room tied to what ever the other missing 20k is at. Personally I would not bother zoning.

Understood about emitters… just was curious if their was a design temp, like 160 F to start from.

Understood about AWT, only 1% of winter heating days at or below that temp.

Posted layout.

Gordy

Do you mean 48k total heatloss?. I have a 2000 SF ranch built in 52 lots of glass . Not renovated. design temp is -5 I'm at 21 btu's SF. I still think it's off. Typically heat loss programs are 15-20% padded.

bmwpowere36m3

Gordy said:

Do you mean 48k total heatloss?. I have a 2000 SF ranch built in 52 lots of glass . Not renovated. design temp is -5 I'm at 21 btu's SF. I still think it's off. Typically heat loss programs are 15-20% padded.

Yes, 48k total. You have any experience with the SlantFin tool? I do have quite a bit of windows (Anderson 400 series casements), totaling about 208 sq ft. (9x4.5' bay in living room, 6x3.5' master bed, 5x5' master bath, etc… for example).

Do you know of another good heat calc tool to use?

Gordy

Yes to slant fin, and I have over 500 SF of windows, and doors. Double hung with storms which fair better than thermopanes.

bmwpowere36m3

Gordy said:

Yes to slant fin, and I have over 500 SF of windows, and doors. Double hung with storms which fair better than thermopanes.

So you're saying the SF tool is padded 15-20%? The areas that I'm not heating with emitters (basement/attic staircase, MB closet, garage, hallway near living room and AV closet) I consider cold partition walls in the tool.

bmwpowere36m3

Whats interesting is that my parent's house is the same sq ft, year built, renovated 15 yrs ago, heavy insulation, baseboard throughout first floor… has a Burnham 136 MBH oil boiler (15 yrs old).

When I first ran the heat calc #'s I was thinking something must be way off or the DWH load is not included. Which I know it shouldn't be with priority. They also recently had the boiler setup for cold-start and DWH priority.

Gordy

That's not odd most existing boilers are way oversized. In the day fuel,was cheap. Knuckle heads who choose not to do a heat loss just exchange same size.

bmwpowere36m3

Gordy said:

That's not odd most existing boilers are way oversized. In the day fuel,was cheap. Knuckle heads who choose not to do a heat loss just exchange same size.

So should I take the SF calc and subtract 15-20%? 48 BTUs/hrs should really be 38 - 41 BTUs/hr?

Gordy

My moms house was built in 1910 blown insulation in walls 35 years ago newer thermopane vinyl windows 10 years ago. She has forced air with a 35k furnace 1100 SF.

Gordy

Whn 55

bmwpowere36m3

Gordy said:

Whn 55

Thanks!

While I'm not questioning your knowledge or expertise… is there another tool I can use to verify the heat loss #'s. It would make me feel better as I don't have much experience and can only go on what I've calculated, what's in a similar sized house (parents, which I agree might be too high) and what the supply house calculated.

Thanks again.

WillieJ

My house is 3400 sq ft with about 3000 heated, built in 1978. Design temperature for my location is 19* F. There are three zones- main living area, upstairs bedrooms, and downstairs daylight basement, all in baseboard slant fin type radiators. Three zones seems like plenty for this house.

At design temp, the heat loss for the main living is 24,991, for the bedrooms is 9304, and for downstairs is 15808, per the slant fin calculator, for a total of 50,103 in heat loss for the house. Using 180* water there is a total of 84,075 in radiation in the house, so I am over radiated. The extra radiation allows me to use 150* water at design temperature because at that temperature I am radiating 53,000 BTU.

Right now with 39* outside temp, the boiler is putting out 123* water and the house is quite comfortable. Over the last two years the average boiler run time per cycle is about 46 minutes. The cycle time average has gone up as I have adjusted the ODR curve to more closely match the heat loss.

We only do night setback for the bedrooms. We leave the rest of the house at 71*.

The boiler is a Lochinvar WHN085. This was not the result of proper and careful planning. I lucked out. The installer did a very nice and competent p/s installation job. But I really didn't know that until after the fact when I found Heating Help. He did not do a heat loss calculation. We walked around the house prior to the install and he remarked that I had plenty of radiation. As it turns out, that is the case. I did the heat loss after I started coming to Heating Help. I might have been just fine with the WHN055. We knew the old Weil McLain was oversized at 235,000 BTU.

Glad to see you are doing the careful planning that I didn't do. The expertise of the pro's here is tremendous.

Gordy

I would wager the CDN 40 would be fine.

Gordy

Thing to think about is radiation in the basement if that will be future expanded space.

Actually run the numbers with conditioned basement. Dont forget to change the main level floor factor to heated space below. it may shock you how little it changes.

clammy

In the past I ve done a few homes using mod cons boilers and baseboard and I ve found for the money your best bet is to use panel radiators with thermostatic radiator valves .EI buderus model 11 and 22 .If your stuck using base board go with the slant fin 80 and size it for a max temp of 160 at below your outside design temp ,I have a few customers where I have done this and there very happy but the boiler does not stay in the condensing mode after the shoulder months .The big upside of the panel rads w trv and the proper sizing is you can maintain your boiler staying in that condensing mode .My own system is a mod con with buderus panel rads and its odr is set for a max of 140 at 10 odt and she s at it now with a 20 td purring along modulating down to about 30mbtu .My last months gas bill was 54 bucks heat and hot water . Make sure that your new systems design is done correctly other wise that new mod con will not shine and you will not be happy ,Do yourself a huge favor and have either a califee magintic dirt separator (vertical unit is better IMHO) or Senitial industries eliminator (which I ve seen at supply house looks really nice)Make sure if zoning that your not mirco zoning,and if you mirco zoning take a good look at the boiler minion input and more important is it s modulation on start up (hi fire) and how long it stays there to ensure flame stability before modulating down this is where I see issues where the units will ramp up n down on temp and short cycle ,If mirco zoning think boiler buddy buffer tanks great product and have a few of them out there working great.Do yourself a favor take a better look at your heat emitters ,panel rads give you back moulding in your rooms and seem to just disappear into the room .Im done preaching peace and good luck clammy ps take a look at prestige boilers

bmwpowere36m3

Hatterasguy said:

Now you're pushing it.............if he must heat the garage at 7°F.

Garage is not factored into the heatloss (or sq ft)... I was considering leaving a space on the maniofold if I want to put into a unit heater. But I might just do a big shed/garage out back.

bmwpowere36m3

Gordy said:

Thing to think about is radiation in the basement if that will be future expanded space.

Actually run the numbers with conditioned basement. Dont forget to change the main level floor factor to heated space below. it may shock you how little it changes.

If anything I'd go up to add bedrooms/space. I don't care for living space in the basement, considering it's all below grade with very small windows.

bmwpowere36m3

Now let me ask about radiator sizing. How do you calculate the delta T tru the emitter? Assuming I tie rooms together (same heat loss). If I deliver 160 to the first room, what will the supply temp be entering the next room? Is it based on this equation:

BTU/hr = 500 x delta t

bmwpowere36m3

With regards to the emitter specs, are the supply temps listed as "average" (supply+return/2) or the incoming supply temp (with the assumption of a 20 delta t).

bmwpowere36m3

Hatterasguy said:

bmwpowere36m3 said:

Now let me ask about radiator sizing. How do you calculate the delta T tru the emitter? Assuming I tie rooms together (same heat loss). If I deliver 160 to the first room, what will the supply temp be entering the next room? Is it based on this equation:

BTU/hr = 500 x delta t

The formula is DT= (BTU/hr)/(500)(Flow rate)

If you're flowing 4 gpm through the loop and one 8' panel sucks up 4000 BTUH, the next panel is going to see a temperature that has dropped by 2 degrees.

Based on the heatlosses and zones I wanted to do, I have to keep the flow to around 1 GPM. I've looked at TACO circulators before and it seems most would run much higher given the distances in the house and headloss of piping.

Gordy

Just rember with the cdn 40 your indirect is only going to get its the output of 35k. Most gas water heaters are 30-36 k. Raise indirect temp and mix down you will be fine, and don't use setbacks

bmwpowere36m3

Gordy said:

Just rember with the cdn 40 your indirect is only going to get its the output of 35k. Most gas water heaters are 30-36 k. Raise indirect temp and mix down you will be fine, and don't use setbacks

The crown megastore is rated at something like 100k BTU max input. I know the knight boiler you can have a seperate DWH supply temp (default 180) from the heating zones.

Mix down?

bmwpowere36m3

null
Store the water in the tank at 160? Why so high, I was thinking 120-140... planning on a 50 gal.

Gordy

I will add water heater tank temps below 130 is a breeding ground for legionella.

bmwpowere36m3

I've been rerunning the heat calcs… using the SlantFin, Crown Boiler (spreadsheet) and loadcalc.net (supposedly based on Manuel J).

I've started with just walls, floors and ceilings (no windows, doors, infiltration or interior walls).

S/F: 24.7 MBH
Crown: 24.1 MBH
loadcalc: 22.1 MBH

About a 10% difference between S/F and loadcalc.

I found a bunch of window efficient tags which indicate they are 0.28 (u-factor). SlantFin lists double glazed as 0.65 and triple 0.36. The windows are Anderson "dual pane low-e glazing with argon".

Would it be wise to use that value (0.28) or play it safe with 0.36? I'm thinking 0.36 as before I had entered 0.65, about a 4 MBH difference. I know its small, but it all adds up right?

SWEI

If you have an NFRC U-value for the specific windows installed, use that. Be sure you use rough opening dimensions (not the daylight opening or glass opening size.) There's plenty of headroom in the calculator already.

bmwpowere36m3

SWEI said:

If you have an NFRC U-value for the specific windows installed, use that. Be sure you use rough opening dimensions (not the daylight opening or glass opening size.) There's plenty of headroom in the calculator already.

Awesome!

bmwpowere36m3

Hatterasguy said:

bmwpowere36m3 said:

Would it be wise to use that value (0.28) or play it safe with 0.36? I'm thinking 0.36 as before I had entered 0.65, about a 4 MBH difference. I know its small, but it all adds up right?

Windows, although they lose quite a bit of heat per square foot, are negligible due to the rather small percentage of square feet in the building. .28 would be the best of all windows. If you run the calculation with .33, there won't be much of a difference.

Now, the walls............the U factor for the walls is serious business. .02 difference in a wall calculation affects the final result significantly. A serious error is usually made in the wall calculation because of the studs. Their R value is miserable as compared to the insulated wall and the combined R value needs to take this into account. Most folks don't.

Infiltration is the biggest variable of all. The estimates can be wildly off due to the lack of substantive data.

Like I said, I was using the default double glazing setting in S/F without thinking about the number (0.65). If I enter 0.28 it's a 5000 BTU/hr difference. I guess it seems small, but all these values add up.

According to the tools:

Walls: ~7000 BTU/hr
Ceilings: ~3000 BTU/hr
Floors: 15000 BTU/hr (first floor, hardwood, over unheated basement).

I always thought the ceilings (0.022, ~ R46) would be the biggest loss, I have R19 and R30 (crisscross) installed. I'm surprised by the floors… 0.15 (~ R7). For the walls the value is 0.07 (~ R14), that agrees with a breakdown I found that included the R value for studs (2x4) at 15% wall coverage and R15 insulation at 85% wall coverage and sheathing/air barrier film/drywall at 100% wall coverage.

Jean-David Beyer

I have an 1150 or so square foot cape cod house. The downstairs is a radiant slab at grade for heating downstairs and Slant/Fin baseboard upstairs. Upstairs is one zone. Downstairs is another zone. There is also an indirect fired domestic hot water heater in the system.

The heat loss upstairs is about 1/4 that of the downstairs, but requires hotter water temperature. The boiler is an 80K (input) BTU/hour W-M Ultra 3 gas fired. It will modulate from 80k down to 16K BTU/hour.

The downstairs runs just fine within the modulation range of the boiler; it even condenses until the outdoor temperature gets down to 8F, and design temperature around here is 14F.,

On the other hand, the upstairs zone must be set to run at a higher temperature than I might prefer so as to have the baseboard dump out enough heat to prevent the boiler to rapid cycle. That zone will condense only until the outdoor temperature gets down to 30F. I replaced the 3-foot long baseboard in each of two rooms with 14-foot long baseboard in each room to get the average water temperatures down.

In other words, even though I have only two zones, their heat needs are such that if I run with the water temperatures I want upstairs, it rapid cycles. On the other hand, if I combined those zones, there is no way I could get the temperatures I want in those two zones.

I wish they were making a 40,000 or even 50,000 BTU/hour mod-con boilers when I bought mine. I do not know if they do even now.

bmwpowere36m3

Jean-David Beyer said:

I wish they were making a 40,000 or even 50,000 BTU/hour mod-con boilers when I bought mine. I do not know if they do even now.

I was looking at Lochinvar Knight boiler (wall mounted)… WHN055 (55 MBH input, 44 MBH IBR) with a 5:1 turndown. So I think it can modulate down to 8.8 MBH. I was told to run a WHN085 (80 MBH input, 64 MBH IBR) and it should be able to modulate down to 12.8 MBH.

I think their Cadet models go a little lower…

SWEI

Modulation numbers are generally quoted as inputs (firing rate.) Outputs vary by water temp and firing rate, with lower firing rates and lower water temps increasing efficiency (to 98% in many cases.) Use the input numbers to avoid confusion. The WHN055 has a minimum rate of 11k, the CDN040 was 8.5k, now they say 9k. Dunkirk has one that bottoms out at 10k, I think Viessmann is 12k.