Heat loss calculation gut check

Allough

Hello,

I'm in the middle of building a new house. I am doing a lot of the work myself but hiring sub contractors for parts I don't feel comfortable with like electrical, drywall, and for installing the eventual boiler. While I love doing as much work as possible myself, I have no interest in installing something that breathes fire without having some sort of training

Anyways, I would like to do radiant flooring. Since I would like to do the manual labor myself (installing the pex and transfer plates between the joist), and hire someone local to install the boiler, I had been looking at online companies first for materials and design.

Being the untrustful, research-it-myself kind of guy I attempted learning heat loss calculation myself because the number I was supplied with by a unnamed radiant company (from now on called: URC) looks wrong.

Project Assumptions: 0F outside, 70F inside.
Closed loop heating, supplied by boiler.
2x6 R22 walls, R49 ceiling, R3.2 floor with full unheated basement underneath.

1. There is 1,893 sqft of heated space
3. A total of 14 windows that have 399 BTU/h loss each per Andersen.
4. A sliding glass door with 1464 BTU/h loss (Almost cried when I found that out)
5. A fiberglass door with 467 BTU/h loss

These are the same numbers sent to the URC, along with a copy of the plans.

They came back at me with a total heat loss of 39757 BTU/h, and recommending a 100k BTU boiler.

My own calculations, done room by room, comes up with 23375 BTU/h and the RadiantWorks tool recommends a 51k BTU boiler.

Am I right to question the heat loss calc done by the URC?

JeffM

This doesn't answer your load question, but if you're building new I'd strongly suggest looking in to one of the radiant tubing systems that installs above the subfloor (Viega Climate Panel, Warmboard, etc). They perform better so you will have some energy savings, and are lots easier to install which will save you time and frustration. More money up front, but worth it in my opinion.

bmwpowere36m3

There are a lot of variables when it comes to heat loss as I'm personally learning.

Infiltration seems to be the biggest variable and can almost double your heat loss. 24,000 BTUs/hr that's only 12 BTUs per sq ft...

I would ask the subcontractor if they calculated 40k, why are they recommending a boiler twice the size?

Allough

@JeffM‌
I agree with you JeffM, I really like the Warmboard product. However I started this house about 4 years ago, and am building it as I get the money so I don't have a major loan. I already have 28x28ft of it completely finished, except for heating which is supplied with Cadet Softheat's until I can get the radiant in this summer.

In the beginning I hadn't heard of Warmboard, and the price of the Uponor Quiktrack seemed extreme at the time.

Long story short, if I added Warmboard now, I would either have to tear up 760 sqft of finished floor or have a rather large drop in my floor where the "old" and "new" floors come together. (Right smack dab in the middle of my living room).

I wish I had planned for Warmboard from the beginning, but my wife hates of the idea of water pipe sandwiched in the floor anyways.

Don_197

Whether its their 40k or your 30k number.....you should end up with the same size boiler......approx a 50k. I wouldn't sweat it.......you aren't going to find a decent boiler with less than 50k input.

NJ, Designer

Of course you should question the URC estimate, That's how a lot of suppliers make money, Did you pay them for the load calculation? what program did they use?

"Project Assumptions: 0F outside, 70F inside."
WHAT'S YOUR LOCATION?
"Closed loop heating, supplied by boiler".
STAPLE UP GYPCRETE OR WARMBOARD?
"2x6 R22 walls, R49 ceiling, R3.2 floor with full unheated basement underneath."
WHAT'S YOUR CEILING HEIGHT? ROOF CEILING COMBO OR ATTIC ABOVE? WHAT'S YOU CONSTRUCTION TIGHTNESS?

1. There is 1,893 sqft of heated space
"3. A total of 14 windows that have 399 BTU/h loss each per Andersen."
WHAT IS THE U VALUE OF THE WINDOWS AND THE SHGC VALUE? WHAT IS THE SQ AREA OF THE WINDOWS?
"4. A sliding glass door with 1464 BTU/h loss (Almost cried when I found that out)"
AGAIN WHAT'S THE RATINGS FOR THE DOOR AND THE SQ AREA?
5. A fiberglass door with 467 BTU/h loss
"

Trying to learn load calculation you can get some free courses from taco's web site, http://flopro.taco-hvac.com/ or go hire someone that has experience for a few dollars and get a room by room load,

Hope this helps you and good luck.....

Allough

Thanks Don, I guess that's really what I wanted to know. A 100k boiler seemed insane overkill since something like a TT PT110 "only" modulates down to 30k, and I have the heating area split into two almost equal zones.

If only one zone calls for heat at a time, it would be better to have something that can modulate down into the 12 - 20k range right?

@bmwpowere36m3‌, Some of my interior rooms came out with a 9.5 BTU/h calculation, while other bigger ones with exterior walls came up with 15.5 BTU/h .
The "room" I'm most worried about having wrong is my living/dining/kitchen. All three are open to each other with only a half height wall between the living and dining rooms. Since its open, I have to calculate the heat loss as one big room.



Its roughly 782 sqft, 8ft ceiling, and 58 ft total of exterior wall.
I came up with 11.91 BTU/h , and a total required BTU/h of 9329. This is using the RadiantWorks Pro tool.. It seems really low for a big open room like that.

icesailor

"" Of course you should question the URC estimate, That's how a lot of suppliers make money, Did you pay them for the load calculation? what program did they use? ""

That's total ****!!!!!!!

Suppliers are in the business of selling their products. If they don't sell their products, they get bought out by those that do sell products. They also don't want to sell undersized boilers that don't work properly and they have to take back the old one and give away a new one. If you are on very good terms with your local supply house, sometimes, you can get very good deals on things taken back where they are trying to get some of their money back.

I've been following this forum for many years. In this last two years, I can't believe all the undersized systems going in by people given mis-information by Internet Experts (not from here), and posted here because of their problems.

Its a good thing they don't do it like they used to. Those old gravity systems. Overpowered and under pumped.

Now, they are underpowered and under piped and over pumped.

Progress, not perfection.

Allough

@bmwpowere36m3,
This isn't from a local subcontractor, its from an online radiant company.
My sneaking suspicion about the 100k boiler is because they are also the seller of the boiler. In the end, all I was wanting to use them for was the design of the system, the heat loss calculation, and supplier for the pex pipe and transfer plates.

I don't think I am going to be using them for anything now that you guys confirmed my suspicions about the boiler being way to big.

RobG

What kind of boiler, type of PEX and type of plates are they quoting you on?

Allough

Western PA, 16362
Staple up, with 4ft long 0.16 gauge transfer plates. 8in OC
8ft ceiling, we used trusses with the insulation directly above the ceiling. So yes there is technically an attic, but it is unheated space open to the outside.

Windows
U: .3
SHGC: .32
Area: 14.7

Glass door
U: .3
SHGC: .32
Area: 34

5. A fiberglass door
Can't find this anywhere. Its a 36" door of standard height, and according to the sticker an R value of 4.
So an Area of around 19.

Thanks for the link for the Taco courses. I love these kind of things. I'm the type that likes to learn everything I can about what is going in my house.

Allough

RobG said:

What kind of boiler, type of PEX and type of plates are they quoting you on?

Thankfully the quote and heat loss calc was free, nor would I have paid for one that wasn't a local contractor.

They neglected to supply me with the brand of boiler, and they wanted me to use their "special" thin wall pex that doesn't have an O2 barrier. It sounds like an awesome way to get kinks while pulling it and for my feelings on the thin walled pex, no one ever says how much they love the thinner ply garbage bags better than the good ones.

That's not happening in my house. That being said, Pex-AL-Pex seems to be a match made in heaven for underfloor heat where expansion would make noise since its not contained in concrete or something like warmboard. I was going to ask about that later!

JeffM

Since you've got acceptable logic for putting the tubing up from below the subfloor, I would steer away from the thin-wall PEX and urge use of standard SDR-9 PEX with oxygen barrier (which is the standard industry product). I also urge use of extruded heat transfer plates screwed up to the bottom of the subfloor. These are a tight fit to the tubing, and both minimize expansion noise and provide very good heat transfer to the floor. I recently did a radiant retrofit to my kitchen using such plates and 3/8" nominal oxygen barrier PEX, and output is good and the system is silent. The extruded plates are more money than the thin formed plates which staple over the tubing, but are far easier to install, quieter, and perform better - worth the investment. Don't forget to put up as much insulation as you can fit below the floor to drive the heat upward.

bmwpowere36m3

They seem to be missing floor heat loss... My house, 1600 sqft, single story ranch, uninsulated and unheated basement the loss thru the floor is almost a third of the total home's heat loss.

For example when I first ran a set of heat loss numbers using the Slant Fin tool (IBR method), it gave me ~61,000 BTUs/hr for a 1600 sqft house, which is about 38 BTUs/sqft.

I started playing with the tool more, realized that a lot of the variables are U-Factors.... and things started to click.

Without going into too much detail I'm now in the ballpark of 42,000 BTUs/hr, which is ~26 BTUs/sqft. The biggest variable being infiltration, which for me ranges from 7-14k BTUs/hr (0.5-1 ACH) and is hard to estimate what it really is.

Point is, whether its 30 or 40k doesn't really matter. The boiler size will likely be 50 or less depending on how good your heat loss calc is (or pay for one).

Allough

@bmwpowere36m3‌
You are right. The RadiantWorks tool from Watt shows the downward loss on the form, but I can't get it to add to the final total. Doing a manual calculation It looks more like I'll be around 5 BTU/h higher on most rooms, and 12 BTU/h higher on two of my rooms. (The big open space being one of them)

My worst offender would be 27.55 BTU/h sqft, with all but two rooms being under 20 BTU/h sqft.

Either way, I'm still good with a 50k boiler. I do however want to learn how to do an accurate heat loss calculation because I'm interested in radiant floor design in general.

I'll try out the Slant Fin tool.

Allough

Slant Fin tool with the same numbers as the RadiantWorks tool returns 52066 BTU/h total!

bmwpowere36m3

Allough said:

Slant Fin tool with the same numbers as the RadiantWorks tool returns 52066 BTU/h total!

You have to be careful with S/F tool… as I learned. I get 44-54k BTUs/hr (0.5-1.0 ACH). The big hitter is the floor, 20k BTUs/hr assuming in the S/F tool "wood floor over enclosed unheated basement", U-Factor 0.15 or R-Value 6.7.

I ran a test with a wall the same sqft as the floor space… it appears the S/F tool assumes the outdoor temp is the same as the basement temp. This leads to huge floor loss numbers given that floors aren't usually insulated.

With temps in the 20s here, by basement has been at 45 or so…. so the heat loss isn't as drastic as predicted by S/F.

bmwpowere36m3

Hatterasguy said:

And, yet another failure by the SF tool.

No small wonder why their results are always inflated.

Right!

Lets just say the basement maintains a temp of 40F, then the 20k floor loss drops to 9k.

For sure, heat is being lost thru the floors and out the basement walls… how much? Again, another variable to estimate. How much of the foundation is under the ground and what is the temp of the ground? The basement floor slab acts as a big heat sink, warmed by the ground.

bmwpowere36m3

Hatterasguy said:

The basement is warmer than 40°F unless you've got all the windows open down there.

Yes, but is that because of heat from conditioned spaces above or the ground (radiating thru below grade foundation walls or floor slab)?

I don't think 6' down the soil temp is 40 or 55* when its single digits outside. Basements aren't usually that cold, but heat is being drawn from floors above.

I don't think you can assume the basement will be 55* with no heat input. So obviously there's heat loss to the basement that the boiler needs to cover.

I just don't know what's the best way to estimate it.

Rich_49

Please see the thread titled "Rescue help wanted" in this same radiant heating section . Do not use the system or purchase anything from the company you are questioning , you will be sorry just as Laurelie is .
Pay a qualified person to design your system , preferably one that has knowledge of building science also . There are several guys here who do this .

Allough

@bmwpowere36m3‌ @Hatterasguy‌
At the moment 54x28 of my house is uninsulated and unheated, with a 10in block basement underneath that section. The basement is 8ft tall, with 7 ft buried. Last week it was heading negative temperatures several nights. I made a note of it one night because it was -4 outside and almost 20 degrees warmer in the basement. There is definitely some heat pulled from the ground, though at some temperature the heat would have to start flowing the other way due to ground temps being below freezing above the frost line.

bmwpowere36m3

bmwpowere36m3 said:

You have to be careful with S/F tool… as I learned. I get 44-54k BTUs/hr (0.5-1.0 ACH). The big hitter is the floor, 20k BTUs/hr assuming in the S/F tool "wood floor over enclosed unheated basement", U-Factor 0.15 or R-Value 6.7.

I ran a test with a wall the same sqft as the floor space… it appears the S/F tool assumes the outdoor temp is the same as the basement temp. This leads to huge floor loss numbers given that floors aren't usually insulated.

With temps in the 20s here, by basement has been at 45 or so…. so the heat loss isn't as drastic as predicted by S/F.

Hatterasguy said:

And, yet another failure by the SF tool.

No small wonder why their results are always inflated.

Actually I made a mistake with regards to floor heat loss... I was thinking about it wrong. I think the S/F tool is pretty spot on actually. It lists:

"Wood Over ENCLOSED UNHEATED Space>No Insulation, Finish Flooring, Pine stub-floor"

as a Factor 0.15, roughly R7. However the actual R-Value (1/2" plywood, 3/4" hardwood and roofing felt) is closer to R1.5. So given those values, by using a higher R value... S/F is in a sense lowering the delta t between indoor/outdoor temps. In my case ~ 55* assumed in basement, when ODT is 7*.

icesailor

bmwpowere36m3 said:

bmwpowere36m3 said:

You have to be careful with S/F tool… as I learned. I get 44-54k BTUs/hr (0.5-1.0 ACH). The big hitter is the floor, 20k BTUs/hr assuming in the S/F tool "wood floor over enclosed unheated basement", U-Factor 0.15 or R-Value 6.7.

I ran a test with a wall the same sqft as the floor space… it appears the S/F tool assumes the outdoor temp is the same as the basement temp. This leads to huge floor loss numbers given that floors aren't usually insulated.

With temps in the 20s here, by basement has been at 45 or so…. so the heat loss isn't as drastic as predicted by S/F.

Hatterasguy said:

And, yet another failure by the SF tool.

No small wonder why their results are always inflated.

Actually I made a mistake with regards to floor heat loss... I was thinking about it wrong. I think the S/F tool is pretty spot on actually. It lists:

"Wood Over ENCLOSED UNHEATED Space>No Insulation, Finish Flooring, Pine stub-floor"

as a Factor 0.15, roughly R7. However the actual R-Value (1/2" plywood, 3/4" hardwood and roofing felt) is closer to R1.5. So given those values, by using a higher R value... S/F is in a sense lowering the delta t between indoor/outdoor temps. In my case ~ 55* assumed in basement, when ODT is 7*.

Can you explain just what exactly that factor of
"0.5" means in relation to how the S/F program makes computations?

bmwpowere36m3

@icesailor

0.5? Based on my experience, cross-checked with other "IBR" calculators, most of the "factors" in the Slant-Fin tool are U-Factors (i.e., R Value = 1/U-Factor)… the exception being infiltration. For infiltration I found the factor 0.009 = 0.5 ACH, 0.0135 = 0.75 ACH, 0.018 = 1 ACH and so on.