High efficiency furnace

Originally Posted By: Mark Leonard
This post was automatically imported from our archived forum.



If there is a HRV in a house can the combustion air intake for the furnace be left inside the house.


The furnace is a Concord 90+ high efficiency furnace. The furnace is in a utility room closed off from the rest of the house. The air intake is stubbed out of the furnace with a 90 on it. The HRV is in the same room but there appears to be no vent from the HRV to supply the furnace with fresh air.


Any suggestions?


Originally Posted By: phinsperger
This post was automatically imported from our archived forum.



There are some furnaces that had an option of using inside combustion air. As an HRV is a balanced system, I don’t think it has a bearing on the furnace installation you describe. You would still need a supply of air to the furnace as you would a mid-efficiency (undercut of door, grill in door, etc) to the amount dictated by the manufactuer.


It would however be in your clients best interest to route the air intake from outside simply to reduce depresurization of the house. Less deprsurization means less uncondition air infiltrating in around doors, widows, etc. This will of course result in lower fuel bills.


--
.


Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: rcooke
This post was automatically imported from our archived forum.



Mark Leonard wrote:
If there is a HRV in a house can the combustion air intake for the furnace be left inside the house.
The furnace is a Concord 90+ high efficiency furnace. The furnace is in a utility room closed off from the rest of the house. The air intake is stubbed out of the furnace with a 90 on it. The HRV is in the same room but there appears to be no vent from the HRV to supply the furnace with fresh air.

Any suggestions?

Good call in my opinion . I think you can be satisfied with the HRV supplying the home with enough air but feel the door to the Furnace room should have a grill to allow the Air to get to the furnace.
A good way to write it up is suspect air supply shortage to furnace further evaluation by qualified .
I would also write up Service furnace on move in day.
and then suggest to the purchaser they could get the person who services the furnace to give them further advice. This is not a costly fix usually


--
Roy Cooke Sr.

http://Royshomeinspection.com

Originally Posted By: jhagarty
This post was automatically imported from our archived forum.



Mark:


My general reporting comment is that the Fresh Air Intake be extended to the Home exterior when found to be as you described.

Manufacturer's recommendations will list the requirements of Cubic Feet of Air to BTU firing rate. You need the installation manual to accurately calculate.

Side Note:

When there is only one pipe, verify that the line to the exterior is the Exhaust. This past Winter, I found a 3 year old York Stellar model that was piped to draw combustion air from the exterior and was exhausting to the Basement. CO levels on the 1st Floor Kitchen were 50+ ppm.

This was a 3 year old system that had been serviced Spring and Fall each year after installation. No one noticed the improper installation. Homeowners were experiencing symptoms of CO Poisoning but were never tested as the service records indicated everything was OK.

Seller is now in litigation with the HVAC Vendor.


--
Joseph Hagarty

HouseMaster / Main Line, PA
joseph.hagarty@housemaster.com
www.householdinspector.com

Phone: 610-399-9864
Fax : 610-399-9865

HouseMaster. Home inspections. Done right.

Originally Posted By: Mark Leonard
This post was automatically imported from our archived forum.



Thanks for responding so quickly. Good ideas on verifying which pipe was going outside and a vent on the door.


With the HRV keeping a balance of air in the house, what it takes out it brings back in. This would mean that if the house is starving for air the HRV would only keep the same amount of air in the house not suppling any more for combustion of the gas.

With the furnace relying only on air from the inside of the house would it not compromise the efficiency of the furnace? As well the basement has been converted to an apartment with a separate entrance. The rest of the house being closed off. Therefore only the air in the basement supplies the furnace.

The house is 1500sq feet so maybe the furnace doesn't need that much air for combustion?
Quite correct in saying that the air intake should be taken outside. Or should have been in the first place.


Originally Posted By: rcooke
This post was automatically imported from our archived forum.



This could be a great time for an HRV expert to give his opinion .


We have many things that can add to negative pressure in the home from bath room and Kitchen exhaust to Dryers and Induced draft Hot water tanks .



Roy Cooke Sr.


http://Royshomeinspection.com

Originally Posted By: pbolliger
This post was automatically imported from our archived forum.



I found this on the Popular Mechanics web site.


http://www.popularmechanics.com/home_improvement/how_it_works/1275121.html?page=2&c=y

Very interesting since I have never seen one or heard of one in my neck of the woods.

The air intake ,looks like it comes from the outside, so I wonder about taking air from inside the closet.

Hope this helps.


Originally Posted By: bwieczorek
This post was automatically imported from our archived forum.



Mark:


I had a a 90 plus rheem furnace in my last home that used air from the utility area where the furnace was installed. I had louvered doors on the room where the furnace was located. There was no necessity for mine to draw in air from the outside. I questioned both the installer and code enforcer for the county.


Originally Posted By: phinsperger
This post was automatically imported from our archived forum.



Mark Leonard wrote:
With the HRV keeping a balance of air in the house, what it takes out it brings back in. This would mean that if the house is starving for air the HRV would only keep the same amount of air in the house not suppling any more for combustion of the gas.

For all practical sake - Yes.

Mark Leonard wrote:

With the furnace relying only on air from the inside of the house would it not compromise the efficiency of the furnace?

Yes, as compared to a closed combustion system by routing the in take from the outside.

Mark Leonard wrote:
As well the basement has been converted to an apartment with a separate entrance. The rest of the house being closed off. Therefore only the air in the basement supplies the furnace.

A great source or air infiltration in many home comes from around the rim joists area, utility penetrations, poor window and door sealing, other flues, etc.

To be on the safe side when in doubt, most HVAC's will simply add a supply duct, grill, etc.

Alternatively, you could also have your client (when they own the home) get an energy evaluation done through the EnerGuide for houses program. Part of the evaluation will actually perform a depresurization test at which time the infiltration sources will be quite evident. As well, the real aggregate amount of infiltration can be accurately determined.

However, my first choice would still be just to route the intake to the exterior to get;

- Greater heating efficiency because you do not have to heat the cold infiltrated air that came in to replace the air that was sucked out by the furnace for combustion.

- More humidity. Although the HRV will offset much of this.


--
.


Paul Hinsperger
Hinsperger Inspection Services
Chairman - NACHI Awards Committee
Place your Award Nominations
here !

Originally Posted By: pbolliger
This post was automatically imported from our archived forum.



First is read information from the mfg.‘s plate on the unit. Second does the install follow the mfg. install recommendations? If not then does your local AHJ override that ? Get an idea of room size for category 1 or category 2 FAU’s. Why? Because natural gas needs a 10 air to 1 gas ratio for clean burn.


Here is a formula courtesy of Peoples Energy of Chicago LXWXHX20=Btu’s L=length of room , W=Width of room. H=Height of room x20 ( 20 is a number gas company uses in its calculations for unconfined spaces) That is a 8’x25’x33’ room or 6,600 ft 3 “cubed” minimum room size for 132,000 Btu’s (max) before it turns into a “confined space” .


This formula will tell you the max number of Btu’s that room can “support” the Cat 1, 2 FAU to operate safely.


Remember the dilution air and circulation air are included in this calculation. Finished basements are a big problem with respect to Carbon Monoxide production. People choke off the furnace in the basement without realizing it. No CO detector and you have a local new story about a dead family…


For Category 3 and 4 condensing units that are positive pressure , this is not needed . You take air from the exterior of the home as per mfg. Now why would anyone go against that and use inside air and risk DEATH by installing it in a closet?? What is the point of using a high efficiency unit and de-rate the efficiency or not get the best performance out of it. If you have a sealed system Cat 4 then it gets it's combustion air from the exterior and pushes products of combustion outside.
They have special double PVC venting pipes just for that or else you can do the two pipes offset twelve inches from each other if you don't want two holes in your wall.. I include graphics..

Check the NFGC (National Fuel Gas Code) to thoroughly understand what you are looking at .

Do not think that just one louvered vent is enough. Metal louver have to be in pairs . One on the top within 12 inches and one near the floor within 12 inches with the calculations of 1 sq. inch for every 1000 btu's. Wood louvered doors have 25 % free areas..

CO kills
Any questions?


Originally Posted By: pbolliger
This post was automatically imported from our archived forum.



http://www.nachi.org/bbsystem/usrimages/F/Furnace_vent.gif ]


[ Image: http://www.nachi.org/bbsystem/usrimages/F/Furnance_vents004.jpg ]


[ Image: http://www.nachi.org/bbsystem/usrimages/F/Furnance_vents005.jpg ]


[ Image: http://www.nachi.org/bbsystem/usrimages/V/Venting.gif ]