Sizing new rooms for forced warm air heat

John Barry

how do I size a new addition for forced air heat or can I use the slant fin heat loss calc

Ken_8

John,

A heat load calculation is a heat load calculation - regardless of the form of heating used.

The Slant Fin program works well for any heating system.

Which begs the question, why would anyone want scorched air heat in the first place?

If you stay in the scorched air mind-set, remember, duct sizing, register size and location and return air ducting are far more important parts of the puzzle and end result than the basic heat load calcs.

Granted, the first step is to know the load via these calculations, but that's like saying I need 12 ounces of liquid in a glass to quench a thirst. What's IN THE GLASS is far more important than the size of the glass - as long as it is adequate!

Can you see where I'm going here?

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Weezbo

John....

i understand you you have a forced air furnace and you would like tofigure out how much heat needs to be delivered to the area.....before i go too far do you have zoning or pritty much one t stat?.....some times a new plenum round needs to be cut in to allow sufficent cubic feet per min of heat to be delivered..return ducts are not just a nicety they help the balance of the home...sometimes you can place zones with a Booster fan to deliver some btus far away..depending on the level or standard of your construction your heat load may increase so much so that your existing heat plant wont suffice. if after determining the BTU's per square foot that is required to heat the home you find it to require a larger heat source than you now have...please consider some wet heat. it has certain advantages ...distribution of heat that is controlled by zoning that doesnt produce unhealthy blasts of dust etc.no noisy fan motors etc.depending on the level of the current installation you may need to add insulation to areas of your existing home to conserve energy. unlike wet heat that can be Dialed down as it were . simple speed drives are not really the way to roll as the fire chamber is still banging and booming and if the air flow isnt there it may shorten the life of an existing system.wet heat can be dialed in through coil temps and speed drives rather well,with no particulairly detremental effects ..... Newer burners are all about efficentcy..with water as the means of distribution of heat it is not only quiet it can be controlled to within a very close tolerance which further increases your comfort level both financially and environmentaly....you need to do a heat loss calc so theres a free programme on may sites you can use. theres one here although i've yet to give it a test run...it is from slant fin...i happen to like slant fin boilers with riello burners so i will reccommend another from wirsbo. and i looked at another hvac programme called Elite recently that i thought had a fairly strong emphasis on HVAC.Good luck*~/:)

Boilerpro_3

I disagree

convective heating load calcs give different results than radiant heating calcs. With convective heating, air infiltration losses are higher, so loads are higher. And in addition, if the results of government studies are true, you also have to add additional capacity for the estimated 15 to 25% loss from the ductwork due to leakage into exterior walls, attics, etc, especially with typical installation methods using wall cavities as ductwork. This loss is only about 7% for hot water systems. If the ductwork is poorly balance, you will again see an increase in heat loss.

Boilerpro

Ken_8

Not so.

The best comparative study to date was a Canadian one done about a year ago.

The notion that infiltration is less of a factor in radiant heated applications was a theorhetical notion that had no basis in fact.

The Canadian study went on to say radiant is merely one more way to heat a home. Most of the radiant component manufacturers "qualified" their claims by saying things like, "It has been reported that 66° radiant systems have rivalled perceived comfort of 68° conventional systems..."

Claims for radiant's superior comfort were anectodal. The Canadian study used scientific methods to test. Unfortunately, much of the anectodal "evidence" is very loudly bantied about as "scientific." It also is hyped by the marketing department, not the R&D guys.

This does much to damage other benefits of radiant and/or hydronic vs. F/H/A IMHO.

Once you get caught up in the confusion between anectdotal and hard science, marketing lies drive the story - until we all actually start to believe it!

I fear you are a victim of such insessant marketing trash.

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Boilerpro_3

Very interesting Ken

I'd like to see that study. I have often noticed much less (often it seems like none)cold air movement down the stairs of two story radiant heated homes versus homes with convective heat. This kind of air movement would seem to indicate that hot air stratification is taking place, creating a hot air layer near the ceiling that will creat stonger air currents through the structure... like a hot chmeny pulling a stronger draft than a cold.

It sure is nice to here that someone is beginning to do testing.
Is there an online source for the test info.?

Boilerpro

Ken_8

Here's the link...

http://www.cmhc-schl.gc.ca/publications/en/rh-pr/tech/01-106-e.html

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Tom_35

warm air vs radiant

I'm located in Arkansas where 99.9% of the heating is from "scorched air". We have cooling in most homes and some sort of forced air device (furnace, air handler, or fan coil) is needed to move the air through the ductwork. So, heating is built into the fan device and radiant is unfortunately even thought of.

Our company has been installing radiant heating for 5-6 years, but usually only in high end homes since the radiant installation is an added investment. Most people want a better looking home as opposed to the best heating system available.

I installed radiant heating in my home when I built it nearly 5 years ago. I have a concrete slab home with the radiant floor heating through tile, hardwood, carpet, and a staple-up for my wife's sewing room upstairs.

I have a 2-stage variable speed Carrier furnace that I use in the early Fall and Spring. When the heating season sets in, I turn the radiant on.

This past winter, I installed an ECR direct exchange heat pump system to provide the heat for the radiant. This system has the actual copper refrigerant lines in the earth as opposed to PE tubing with a water/glycol solution. I have been using a small condensing boiler, which works great, but I wanted to see for sure that I could use the d. e. heat pump to heat the radiant and my domestic hot water before we started offering it to a lot of customers. During the time that the radiant was not working, we had to set the Carrier Thermidistat 4-5 degrees higher than we had with the radiant heating. My wife, who couldn't care less about radiant before we installed it in our home, kept asking on a daily basis when would the radiant system be working.

The boiler capacity is 75,000 BTU while the direct exchange heat pump is a 5-ton system. I used a Tekmar control system for the logic on the system. We left the boiler in the loop and installed the piping and allow either system to provide heating with a manual toggle switch energizing the appropriate system.

My radiant system has 8 zones and has worked extremely well. I doubt that we will ever see radiant as the norm for systems here in Arkansas, but the folks that have experienced it when they go skiing in Colorado are all excited about it---it just becomes a matter of whether they will part with more of their $$ for it vs the pretty stuff on a home. We've never had a customer say that they are sorry they chose to go with radiant though.

Tom Atchley