Boiler Evaluation Criteria?

[BirchwoodBill]

I have ran several models on the HeatLoad for the Central Heating (CH):
Heat Load Pro is 48K /32K (The 32K is without air leakage)
Dana's method using Energy Bill shows a max of 27K with a min of 3K for the 0 HDD
Weil McLain replacement kit is 56K.
Original Manual-J from 1986 is 78K
Whole Host Load Calculator (quick) is 40K

DHW estimate is for indirect between 55 GA and 72 - which is requires 100 BTUh when all of the bathroom showers are running (which is once a year).

Right now, I am compiling a list of Boilers that can modulate to the lower end, since that covers the majority of the colling.
Navien NHB with 95% AFUE has a range of 8K - 80K
HTP UFT with 95.4 AFUE ranges from 8K to 80K
HTP Versa-Hydro with 93.0% AFUE ranges from 10K to 100K

In reading the manual for the HTP Versa Hydro it will modulate the burner to the tank at 1:7
The modulate the water for the heater exchange at 1:10

Trying to figure out if the HTP Versa Hydro will just draw from the thermal mass of the Indirect tank to heat the CH fluid before it fires the Gas to heat the in-direct. Don't know if the control system has enough smarts in the summer months to not turn on the gas for the 15-30 minutes it takes to heat the basement.

Looking for some practical real-world experience to enlighten this software engineer.

 

[NY_Rob]

The HTP Versa-Hydro seems like a nice all-in-one solution... but is there anyone in your area who services them?
Imagine you wake up on a cold Jan morning and it won't fire up? Now what? HTP is in Massachusetts.
It's not like a broken TV where there's no TV repair shops any longer so you just go out and buy a new one the same day. You rely on the boiler to keep your house warm.
I urge you to look in to local support before deciding on your new (complicated/computer controlled/driven) boiler.

 

[Sponsor]

 

[Dana]

What were the design temperatures used in the original Manual-J? It seems remarkably out of sync with current measured reality, even if the original windows were single-pane windows/no-storms.

The new quickie Manual-J is quite a bit higher than the fuel-use implied load too. Did you use the same outdoor design temperature for both? Do you use deep thermostat setbacks at night AND during the day (which would warrant using a lower HDD base, but adding the additional heating degrees to come up to a code-min 68F indoors when specifying the load.)

For the WAG rule-of-thumb sanity check, how big is the house? Is the foundation insulated?

The Versa does the right thing, and won't short-cycle the burner when putting a bit of heat in the basement with just that zone calling.

 

[BirchwoodBill]

The house 2500 sq ft includes the basement. The basement foundation has 1 inch foam on exterior and 2x4 walls with r13 it is heated to 68f. First and second floor is 2x6 construction with R19 and Andersen series 400 awning and casement. Attic is encapsulated with 2 inch closed cell foam and 18 inches blown fiberglass on attic floor. The accurite temperature sensor in the attic shows 32F at -20F outside. The biggest sieve is the front wood door. Numbers should improve with insulated fiberglass door.

The original manual j was done by my father, so I will need to pull his original notes. I recall seeing see -30F. Plus it was over an unheated basement. I am using -12F, in my models with an interior temp of -65F in bedrooms and 68F elsewhere.

I found some of my own data entry errors this weekend and models are driving down. Heat load pro is showing 45k. Still think, I need to review the data on the windows from 1986. Warmboard has my plans so I will see what they come up with.

HTP has not returned my inquiries on a list of qualified installers. Navien got back to me in about 4 hours. There are 20 installers for Navien in the 50 miles radius...several have experience with warm board. Need to figure out who understands hydronics.

Time for bedtime reading from Dan Holohan ... pumping away and other piping options.

 

[Dana]

In 1986 most double panes were clear glass (no low-E) in the range of U0.5-U0.6. A design temp of -12F is about right for your location. A tight 2500' house with 1/3-1/2 of the space mostly below grade with an insulated basement would realistically come under 30,000 BTU/hr. The difference with the Manual-J is probably air infiltration & ventilation assumptions.

An inch of exterior foam isn't sufficient dew point control for a 2x4/R13 wall in your climate, but you may have an interior side vapor barrier(?). Even without the vapor barrier the moisture buffering capacity of the concrete may save you from getting frost accumulation and mold in the above-grade part of the foundation.

BadgerBoilerMN (aka Morgan Audetat) installed an HTP in his own place a year or so ago. He's been talking about maybe retiring, but if not him, he'd be able to refer you to a competent installer. Morgan understands how to do the math on hydronic systems, and all types of radiant floor systems, and has been very helpful on various web forums to people trying to de-bug/re-design their systems. He's also one of the select HVAC pros who won't screw up a Manual-J with 2 thumbs and a big toe on the scale.

Navien's heat exchangers have fairly high pumping head, and are almost always plumbed primary/secondary. They sell a pre-engineered hydraulic separation manifold of the closely spaced tees variety, but it's not a requirement to use theirs.

 

[BirchwoodBill]

When I ordered the Andersen windows back in 1986 I did get the early version of their "performance-glass" - still have the original catalog. Spend a few years working for Andersen on optimizing their production lines. Good product, good company.

Just got the heat bill for January into February for a 1515 HDD and 8.0 Therms/Day - my spreadsheets shows an estimated 23.2K. (80 % of the Gas is for heat and the boiler is 87% AFUE).

For the basement I have a 6mm interior side vapor barrier against the concrete wall - then 2x4 framing and R-13 Kraft paper - which was the approach back in 1991 when the work was done. Bottom plate is pressure treated but on top of plastic. Luckily we have a sandy loam under the house so there haven no moisture problems. All of the concrete was treated before I framed it up. The carpenters also paint some asphalt on the exterior of the concrete back in the day. I found that 2-inches of closed cell foam against the sill plate and header with another 12x10 inches of fiberglass really reduces the heat loss in the basement.

Yep Morgan knows his stuff, his fee is very reasonable for a design. Once Warmboard finishes their tubing layout for the first floor, I hope Morgan will find the mistakes in my DIY heat load. Looks like the demolition will start sometime in April/May and then the fun will begin.

 

[BirchwoodBill]

1986 Andersen High Performance Glass for AW and CW U-Factor is 0.30
2003 Andersen Series 400 Awning Casement HP Low E, U-Factor 0.28
2003 Andersen Series 400 Flexi-Frame , U-Factor is 0.27

The original Manual-J was based on - design temp of -16F and with standard U-Factor of 0.52
Our house has about 500 Sq Ft of Glass - with a HP Glass of approximately 0.30.

 

[Dana]

Without the number of days to come up with the total fuel use for those HDD, or the average outdoor temp for the 8.0 therms/day I can't check the math on the fuel-use heat load calculation.

During the winter the space heating load is way more than 80% of the fuel use. It's usually more accurate to let the solar gain error balance against the hot water/other uses (since solar gain lowers the amount of fuel used), and assume it's all space heating use.

With only sheet plastic between the fiberglass and the foundation there will be some condensation/frost on the above-grade section at times during the winter. Hopefully the moisture accumulated over the winter will be low enough to avoid mold on the upper portion of those studs. The kraft facer is a "smart" vapor retarder, that allows the studs & fiberglass to dry toward the interior, as long as you don't have a vapor-retardent interior finish. (Latex paint is fine, foil or vinyl wallpaper isn't.)

 

[BirchwoodBill]

The basement walls just have latex paint, so things breath.

HDD was 1515 Here is the math I put into the spreadsheet (Shown as attached PDF)...

Spreadsheet calculates: Therms/Day = Therms / Billing Days = 256 / 32 = 8.0 Therms/Day
The next call converts to BTUh = (Therms * 100,000 BTU per Therm/ 24 hr/day = 800,000 / 24 = 33,333
Gas is delivered to the heated garage (10%) Dryer (5%) and the gas fireplace (5%).
I agree that we can ignore the dryer and fireplace - but not the garage and assume 90% - which yields 30,000 BTU per hour.

The Weil McLain VHE Series 4 has a AFUE of 87% (was recently re-tuned to factor specs about 4 years ago).

When I change the design temp in Heat Load Pro to 10F (Sort of, Kind of Similar to January 2018 conditions) it shows 32,656. It looks like the two models roughly correlate with another. The new radiant baseboards for the basement sized for AWT of 105 should help - so the basement warms up slower.

Working on getting on Morgan's queue to apply WrightSoft to the system and get a properly designed system.

 

[Dana]

Therms per day is meaningless, since not all days are the same average temperature. Therms per heating degree-day is what matters. Your calculation is completely independent of temperature, whereas heat load is ALL about temperature.

From your spreadsheet between 14 November & 19 February you used (182 + 296 + 256= ) 734 therms

During that period there were (1121 + 1752 + 1515 =) 4388 HDD65

So that's (734 / 4388=) 0.16727 therms/ HDD, which is 16,727 BTU/HDD.

At an efficiency of 87% that.s (0.87 x 16,727=) 14,552 BTU/HDD ...

,..which is a load per hour to temperature linear constant of (14,552 /24 =) 606 BTU per degree-hour.

The presumptive balance point is 65F, the 99% outside design temp is -11F, so you have (65F - -11F=) 76F heating degrees.

The implied load is then:

76F x 606 BTU/F-hr = 46,056 BTU/hr. (Within measurement error of the Heat Load Pro's 48K)

At +10F (WAY too warm a design temp for your location) you'd have 55F heating degrees, and a load of 55F x 606 BTU/F-hr= 33,330 BTU/hr, but if you designed your heating system at 1.4x 33.33K = 46.66K you'd still be covered at -11F, but you'd be losing significant ground on days when it hit the negative high-teens.

The VHE Series 4 came in 4 different sizes, with different BTU in/out ratings. AFUE is tested at 1.7x oversize factor, and it comes in fairly close to the steady state in/out BTU efficiency. If it's oversized by more than 2x for your actual loads it's AFUE starts slipping measurably lower than the steady state efficiency, and at 5 x oversizing it can be pretty dramatic.

How oversized is yours, relative to the 46,000 BTU/hr implied load? (Use only the DOE output number, not the IBR net water number since the boiler is fully inside of conditioned space.)

 

[BirchwoodBill]

Thanks for the help on the model. Will update my spreadsheet.

VHE-4 Boiler Input is 100K, DOE Gross is 87K and IBR Net is 75.7K - AFUE is 87.1% - side-vented. A little bit under 1.9.

 

[Dana]

At ~2x oversizing the hit is small enough when the boiler is inside conditioned space to not really matter- it's "within the noise" of other error factors, so the ~46-48K load is probably close to reality. You'd do fine with a ~60K-in cast iron boiler, but 70K would be better for covering Polar Vortex cold snaps.

The NHB-80 or UFT-80W or Versa would all be good choices. The NHB would require primary/secondary plumbing with a hydraulic separator, but that probably won't be necessary with the UFT.

As for other boilers:

The Lochinvar WH-056 or KH-055 (floor version) would cover it (7.6K- 52K-out), but the WH-086 or KH-085 (8.1K- 81K -out) would give you more margin at the 99%+ temperatures.

The NTI Trinity TX51 ( 7.1K-57,000- in) or TX81 (10.3K- 82K-in) are also in the right range.

I'm sure there are others.

 

[BirchwoodBill]

Thanks for the help - my DIY Heatload spreadsheet is updated in the PDF - showing the impact of more insulation in the attic and a small amount of closed cell form on the Rim joist (which is part of the Warmboard insulation).

I am starting to dig into the plumbing for low temperature systems, since I am replacing the remaining convectors with low temp baseboard that can run between 90F - 105F - same range as Warmboard. Need to review notes on dual-heat-exchanger indirect tanks - since that could be a source of heat during the spring and fall. But I am hiring Morgan, i.e, Boiler Badger) to figure out the plumbing details.

 

[Dana]

The only relevant billing periods for the fuel use calculations are those where there has been a consistent & substantial heat load, and comparatively low solar gains. Running it on the shoulder seasons or annual fuel use has huge distortions from both hot water/other uses and solar gain.

A single winter month's billing period has the additional distortion of not knowing exactly what time of day the meter was read, which can be as big as a 5% error if counting the HDD of both the beginning day and final day of the billing period.