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Not enough Heat in part of building

Starting last summer 2008, we built a 1500 ft2 addition on to the front of our Church. during this addition we installed a new trunk and plenum to our HVAC System. We started to notice last winter that the new addition was not heating well, and was just kind of cold and drafty. We thought it was just because we didn't have insulation or drywall on the walls yet, but after that was on, it was still cold. So we started closing vents in the sanctuary to get more heat/air pressure in the new addition, which did help bring the temperature up. In the Summer we do not have a problem with cooling the building, the same vents seem to have more air pressure. We called the service people and they said the blower speeds had been turned up for the heat, but still little pressure. The trunk is about 30 feet long, and the additions lines are on the far end away from the furnace. The longest line is probably 50 feet from the end of the trunk. Do you think we need to put in an additional furnace to heat the new part?

Re: Not enough Heat in part of building

An additional furnace may be necessary in order to adequately heat the space in question---but the procedure is to have the heat technician make some simple math calculations that can accurately determine how much heat is required---and to compare the result with how much heat output the present furnace can produce.

Churches are usually difficult to heat because they usually have high ceilings---since heat rises, it often requires considerably more furnace heat output to overcome this structural aspect, or to have some way to re-direct the heat moving upward, back down toward the ground level.

A somewhat simple math calculation called a HEAT LOSS CALCULATION or MANUAL J CALCULATION is done.

The basic idea is to calculate how much heat the space in question is losing to the outside atmosphere on a winter's day by considering such variables as thickness of walls, ceiling heights, total square footage, exterior wall composition, the number & size of all windows & doors, geographical location, etc.---all these factors are added up to estimate how many BTUs/hour per square foot are needed to heat the space---this is compared with the listed BTUs/hour as listed on the nameplate of the furnace.

For example, if the calculation is for 3000 sq. ft. of space, and the requirement is 40 btu per square foot, the calculation would be:

3000 sq.ft. X 40 = 120,000 btu/hour to heat the space---the output of the furnace or furnaces would have to, in this case, equal or exceed 120,000 btu/hour to adequately heat the space.

But the required btu's per sq.ft. may be as high as 70 or 90 due to high ceilings, etc., so that the heat per hour requirement could well be:

3000 X 90 = 270,000 btu/hour.

If you Google "heat loss calculation" you will find some on-line HLC's that can be bought for a small sum---or you can have a heating technician in your area do the computer-based calculation.

Also Google "heat loss calculations for churches" (without the quotes), or "heat loss formula for churches" (without the quotes).

Re: Not enough Heat in part of building

Nashua Tech is right about having a Load Calc done but, a 50 foot supply from the end of a 30 foot trunk seems a bit long. Is the supply right off the end of the 30 foot trunk or is it about 18 inches back from the end coming out the side of the trunk? There should never be a run coming out the end of a Trunk, this is important to keep up your pressure. Are there any other supply runs that come off the 50 foot run or is there only the one? If there is more than the one run and the ductwork is not being reduced to make up for lost CFM's you will also lose pressure. Are all your Ductwork and Supply Lines insulated so you don't lose heat? A 1500 sq. ft. addition is not small and as Nashua Tech says your System could be undersized. It sounds to me like your not moving enough air to the addition as you say it's OK when you damper down the Sanctuary. If you don't use both parts of the Church at the same time you could have the two areas Zoned, that you way can only heat one area at a time. At any rate as Nashua Tech says a Load Calc. is the first thing you should do. Good Luck!!! :)

Re: Not enough Heat in part of building

Yes all supply lines are insulated; each register in the new addition has its own supply line coming from the trunk. Yes the lines are coming off the side. The only supply line that has to registers on it is the Narthex, and no the supply line does not reduce down for the feeder from it. Yes we have to have both spaces heated at the same time, simply because it is the entrance to the church. Yes Sten you are correct in saying if we close vents in the sanctuary we do get more air in the addition. Likewise if we close the vents on the stage we get more in the sanctuary and everywhere else down the line of the trunk. Vents Closest to the Furnace/Air handler gets more air.
I've also attached some pictures, and I will attach more when I'm on a different computer.

Re: Not enough Heat in part of building

As Nashua Tech said the first thing you have to do is see if the furnace you are using now is large enough to Heat your Church. If it is then you can look at the Ductwork, after every two or three supply runs the Main Trunk should reduce down to the next size. This will keep pressure in the Main Trunk so the last runs will have enough CFM's to adequately Heat the space. Good Luck!!! :)

Bob Gabrilson
Re: Not enough Heat in part of building

If you can get to all of the ductwork then I would recommend zoning. It'll save on utilities and increase the comfort. Try this first, if the furnace is too small, the zoning will still work with the new furnace. If the existing A/C is large enough, then I would guess the furnace is to. It takes more to A/C than heat (with all the people).

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