Max number of supplies off one trunk and max distance between register and furnace?

[rapida]

How many cfm is it if the blower size is 42? Is it 1400 cfm or 4200 cfm?

[George2]

How many cfm is it if the blower size is 42? Is it 1400 cfm or 4200 cfm?

1,400 equals 3.5 tons. 400 cfm per ton

[rapida]

Thanks again George2. But isn't 1,400 cfm too small for my house? I thought I need 1 cfm per sqft, and that's 4,400 cfm. If I go by 6" supplies at 100 cfm each, with 14 registers up and 9 registers down, I will need 2,500 cfm. Did I miss something? Why they don't match?

[George2]

Thanks again George2. But isn't 1,400 cfm too small for my house? I thought I need 1 cfm per sqft, and that's 4,400 cfm. If I go by 6" supplies at 100 cfm each, with 14 registers up and 9 registers down, I will need 2,500 cfm. Did I miss something? Why they don't match?

We typically size the blower to the A/C needed. We try not to oversize the blower because of the air noise that can occur and the effect on the A/C. Your blower speed is set to the size of the A/C. Let's assume your A/C is a 3 ton. The blower is set to that 1,200 cfm setting for the A/C requirements. That will be the most air your furnace is moving. In the furnace mode, you're moving less air than that. You can change the blower speed to a higher setting in the continuous fan mode.

With all the blower setting now available, noise, if the ductwork is correct, is not an issue. In other words, that furnace comes with a optional 5 ton blower (2,000 cfm). Under normal situations, a homeowner would not have a need for all that extra "power". But with the ECM motor and all the CFM settings available, that 5 ton blower even works with a 3 ton A/C. If said furnace had a PSC motor, that wouldn't be efficient.

Your thinking is correct regarding the supplies verses the cfms available, but that is where balancing the airflow comes in. That is why I like zoning so much. It automatically increases the airflow (heating or cooling) to a particular area when the other zones are satisfied.

[rapida]

We typically size the blower to the A/C needed. We try not to oversize the blower because of the air noise that can occur and the effect on the A/C. Your blower speed is set to the size of the A/C. Let's assume your A/C is a 3 ton. The blower is set to that 1,200 cfm setting for the A/C requirements. That will be the most air your furnace is moving. In the furnace mode, you're moving less air than that. You can change the blower speed to a higher setting in the continuous fan mode.

Does it mean after I extend the duck work, if I have any problem with the temperatures not balanced, I can change the blower speed to high to reduce the temperature difference in the house?

With all the blower setting now available, noise, if the ductwork is correct, is not an issue. In other words, that furnace comes with a optional 5 ton blower (2,000 cfm). Under normal situations, a homeowner would not have a need for all that extra "power". But with the ECM motor and all the CFM settings available, that 5 ton blower even works with a 3 ton A/C. If said furnace had a PSC motor, that wouldn't be efficient.

Your thinking is correct regarding the supplies verses the cfms available, but that is where balancing the airflow comes in. That is why I like zoning so much. It automatically increases the airflow (heating or cooling) to a particular area when the other zones are satisfied.

I thought zoning would help too. But those ICS thermostats are so expensive. George2, do you think I can first try without zoning, and if the comfort level in the sun room or house is not as desired, then add zoning?

Does my plan sound good:
1. extend the trunk line and reduce the size of the extended part to 6"x8" (so that the air to the living room is not "robbed" as much)
2. add 3 supplies to the sun room from the extended trunk
3. if temperature cannot reach desired level, add cold air return to the sun room
4. if it still doesn't work, add zones (do I have to have 3 zones since I have 3 branches, or can I just zone the 2 branches for the main level?)

[wahoo]

Sun rooms by their design are horribly hard to keep comfortable. Aside from a seperate "mini-split" you'll probably not be happy with the results however as it sounds like you want to take the cheapest approach...uh....forget something that will really work. Just let the existing system try and keep up with this addition and assume you'll not be happy with the comfort level. I remember we had a customer who built a large sun room/entertainment room onto his house. I figured the loss/gain and installed a SEPERATE 3 1/2 ton heat pump for this sun room alone. It was a beautiful addition, and they were very pleased (and use the room a lot to entertain!). Do it the cheapest way possible and you'll probably not be happy.

[2old2rock]

You won't be able to zone a sun room against a whole house.

[rapida]

You won't be able to zone a sun room against a whole house.

I was not saying I'd zone a sun room against the whole house. Since I have 3 trunks off the plenum (one for living room area, one for bedroom area, and one for the basement), I was thinking putting each on their own zone.

[George2]

Does it mean after I extend the duck work, if I have any problem with the temperatures not balanced, I can change the blower speed to high to reduce the temperature difference in the house?



I thought zoning would help too. But those ICS thermostats are so expensive. George2, do you think I can first try without zoning, and if the comfort level in the sun room or house is not as desired, then add zoning?

Does my plan sound good:
1. extend the trunk line and reduce the size of the extended part to 6"x8" (so that the air to the living room is not "robbed" as much)
2. add 3 supplies to the sun room from the extended trunk
3. if temperature cannot reach desired level, add cold air return to the sun room
4. if it still doesn't work, add zones (do I have to have 3 zones since I have 3 branches, or can I just zone the 2 branches for the main level?)

You don't need special (expensive) thermostats with zoning. If you run the blower in the continuous fan mode, then you can increase the airflow. Just running the fan (blower) when your using the room will help. Reducing the duct extension is not necessary for that short of a distance. If the door is always open in the sunroom, adding a cold air won't do much good. It sounds like zoning is a real possibility with your duct set up.

[rapida]

I read from another thread that I should not have the supply too close to the end of the trunk line. But having the last supply some 16" from the end of the trunk seems impossible because I'll need one under a window at the end of the house. The trunk cannot run any longer than that. It seems inevitable to have the 6" supplies make a few turns and cross a few joists (not very favorable), if I want to keep some distance between the supply take off and the end of the trunk. Is it really crucial to keep that distance?

Or should I just extend the trunk a little bit to accommodate the addition of supplies, and have the supplies run across the room, instead of having the trunk run across the room?

Another thing is whether I should have 2 or 3 supplies for the sun room. There are two exterior walls. There is one windows on one exterior wall, and there is one patio door and one window on the other exterior wall. Ideally I suppose I need one register by each window/door, making it 3 registers. But the 16"x8" trunk already has got 8 registers. If I add 3 more, would that cause the rest of the house suffer more than if I just add 2 registers? I don't know whether this is relevant or not, the other two trunks in the house, 16"x8" each, one without branching and one branching off to two 14"x8" lines, has 6 and 9 registers respectively.

I have the Infinity thermostat (SYSTXCCUID01) now. If I switch to the cheaper thermostats for zone addition, will I lose the better control on the Infinity system?

[rapida]

Which one is better? Sorry for so many images. I was trying to edit my drawing but all versions are showing up.

[George2]

Which one is better? Sorry for so many images. I was trying to edit my drawing but all versions are showing up.

I would go with option #1 and install a 10"x6" duct register in the basement below for extra heat in that area. The duct register can be closed in the summer.

[George2]

I read from another thread that I should not have the supply too close to the end of the trunk line. But having the last supply some 16" from the end of the trunk seems impossible because I'll need one under a window at the end of the house. The trunk cannot run any longer than that. It seems inevitable to have the 6" supplies make a few turns and cross a few joists (not very favorable), if I want to keep some distance between the supply take off and the end of the trunk. Is it really crucial to keep that distance?

Or should I just extend the trunk a little bit to accommodate the addition of supplies, and have the supplies run across the room, instead of having the trunk run across the room?

Another thing is whether I should have 2 or 3 supplies for the sun room. There are two exterior walls. There is one windows on one exterior wall, and there is one patio door and one window on the other exterior wall. Ideally I suppose I need one register by each window/door, making it 3 registers. But the 16"x8" trunk already has got 8 registers. If I add 3 more, would that cause the rest of the house suffer more than if I just add 2 registers? I don't know whether this is relevant or not, the other two trunks in the house, 16"x8" each, one without branching and one branching off to two 14"x8" lines, has 6 and 9 registers respectively.

I have the Infinity thermostat (SYSTXCCUID01) now. If I switch to the cheaper thermostats for zone addition, will I lose the better control on the Infinity system?

The Infinity stat will work with some zone boards so you will not have to forgo it. Your model furnace might not except the deluxe Infinity zone system. If it will, then the Infinity control would need to be a model Z01 (at the end) not the D01. The other zone thermostats can be cheaper setbacks.

[rapida]

I see. Thanks. Either the contractor wanted to make some extra bucks or wanted to scare me away from zoning, he was telling me I need to have Infinity stats for all the zones in order to work, and it was a shame having to get rid of the existing Infinity stat.

I was not able to add the third option in my last post, which had one take off at the end of the trunk line. Is it really a no-no, or will I get the benefit of extra air flow to the sun room? Here is the drawing.

[rapida]

I would go with option #1 and install a 10"x6" duct register in the basement below for extra heat in that area. The duct register can be closed in the summer.

We are using the room under the sun room as a root cellar in the winter. With the register it will be heated and we'll lose the cellar. Not that we have to have a cellar, but I'd like to see how much benefit we can get from the basement register. Also, should I have all the ducts in the cellar insulated? I am a little concerned about condensation in the summer. The walls are always dry, but nevertheless it's humid in there.

[George2]

I see. Thanks. Either the contractor wanted to make some extra bucks or wanted to scare me away from zoning, he was telling me I need to have Infinity stats for all the zones in order to work, and it was a shame having to get rid of the existing Infinity stat.

I was not able to add the third option in my last post, which had one take off at the end of the trunk line. Is it really a no-no, or will I get the benefit of extra air flow to the sun room? Here is the drawing.

Option #3 would be fine...no prob.

The Infinity zoning system gets confusing. It first begins with the right (newer model) furnace. If you have the newer model, then you can incorporate the Infinity zone system but you'll need to change out your Infinity stat to a "zoning" Infinity stat. If you go the route, the other stats can (just) be sensors.

There are other zone systems that can use your existing stat and any other stats for the other zones. I like the Arzel Heat Pump Pro zone system. Most contractor do not understand zoning. It scares them. It was something that made a lot of sense to me so I did my own studying and research to learn the in and outs. I've sold zoning for 15 years or more with great results.

[rapida]

I finally found a contractor who will do the work. He told me I could expect a maximum 3 degree temp difference between the sun room and the rest of the house. Is it too good to be true?

He also told me I don't need to insulate the ducts in the basement room. I though maybe it's fine in the winter. But should I be worried about condensation during the summer when the AC is running?

Or is it a good idea to put the duct work in the ceiling and insulate the whole joist space in the ceiling?

[George2]

I finally found a contractor who will do the work. He told me I could expect a maximum 3 degree temp difference between the sun room and the rest of the house. Is it too good to be true?

He also told me I don't need to insulate the ducts in the basement room. I though maybe it's fine in the winter. But should I be worried about condensation during the summer when the AC is running?

Or is it a good idea to put the duct work in the ceiling and insulate the whole joist space in the ceiling?

I'm a little surprised he would predict a 3 degree difference. If it happens....great. If you're using the room below as a root cellar, I would wrap (insulate) the duct and the floor joists.

[rapida]

I finally got the work done and couldn't be happier. The contractor put in 3 supplies as shown in the last figure, and one air return.

It turned out the return was not necessary - if I leave it open, the sun room would be warmer than the house when the furnace is on, and cooler than the house when the AC is on. Now I have it closed. The temperature in the sun room is just right, with only 1-2 degree difference between the living room and the sun room. The rest of the house does not suffer from anything that I could notice. The furnace kicks on and off as usual. The temperature of the house is maintained as usual.

Well, although the weather has given us both cold (40 degree) and warm (85 degree) days to test the duct work addition, we didn't have any extreme temperatures yet. My guess is it will be fine. If it doesn't keep up, I'll just open the air return or open the door between the sun room and the living room. I'll post once I know. Now, I am really looking forward to enjoying the sun room in the summer soon.

Thank you all for the expert opinions, especially George2. I couldn't have done it without your help! This is one of the best improvements to the house, and surely the most cost effective!

[George2]

I finally got the work done and couldn't be happier. The contractor put in 3 supplies as shown in the last figure, and one air return.

It turned out the return was not necessary - if I leave it open, the sun room would be warmer than the house when the furnace is on, and cooler than the house when the AC is on. Now I have it closed. The temperature in the sun room is just right, with only 1-2 degree difference between the living room and the sun room. The rest of the house does not suffer from anything that I could notice. The furnace kicks on and off as usual. The temperature of the house is maintained as usual.

Well, although the weather has given us both cold (40 degree) and warm (85 degree) days to test the duct work addition, we didn't have any extreme temperatures yet. My guess is it will be fine. If it doesn't keep up, I'll just open the air return or open the door between the sun room and the living room. I'll post once I know. Now, I am really looking forward to enjoying the sun room in the summer soon.

Thank you all for the expert opinions, especially George2. I couldn't have done it without your help! This is one of the best improvements to the house, and surely the most cost effective!

You're welcome and thanks for the update. I'm happy it works so well for you.