Huge combustion air vents are making my house too cold!

[randyl712]

I've just bought a house, custom built in 2006, Colorado.

The utility room has two 50-gallon gas hot water heaters in it, the room also houses fire sprinkler system with massive water vessel, well pump pressure tank, water softener, etc.

My issue is that the builder put in two huge combustion air vents to the outdoors, each 8" diameter (one high, one runs close to the floor). I understand that the hot water heaters need combustion air, but these large openings into my house are basically turning the utility room into the outdoors, so when it's freezing outside, it's @#$ cold inside, too. Thus the adjacent rooms in the basement are cold, as are the living spaces above the utility room.

Note that there is no insulation in the room other than on the exterior side, above the concrete slab wall in the space between that and the ceiling joists there's maybe 1-2 feet of fiberglass insulation. I've thought about adding 3/8" rigid foam to the concrete walls where I can (there's electrical boxes, plumbing, gas, etc. touching the concrete so it's not possible to add it uniformly) and I plan on insulating the interior walls with fiberglass insulation to help the adjacent rooms stay warmer.

But - this just doesn't seem right. I'm concerned about letting the room get so darned cold - that can't be good for the water softener, the hot water heaters, etc. It certainly isn't efficient to basically have the water heaters sitting in a room that could be 40 degrees in the winter (or colder?).

I've done some rudimentary calculations - There are 2 x 40,000 BTU water heaters in the utility room, which is 160 square feet, ten foot ceiling height = 1,600 cubic feet.

So my question is - given that this room is becoming a walk-in freezer all winter, how do you keep an outdoor vented space from becoming so cold? Two huge holes into my house is the opposite of efficiency and I'm seriously concerned about the heaters and softeners operating in potentially below-freezing conditions!

Thanks for your help. If you ultimately recommend I have a professional come out, I'd love a specific type of expert who would really know what the heck they're talking about. I feel like I certainly could have a local HVAC guy out to look at it but I would want someone who knows what they're talking about.

[jmac00]

interesting? so this Utility Room is on the exterior of the home? It's not in a basement or Garage?

I would get all the pipes (or any pipes) off the cement walls. Use "stand-off" or nail a couple 2x4 to the cement and attach the pipes to the 2x4.

Next insulate the crap out of that room. then I would get some heat in there. sounds like the only way to do that would be electric baseboard heat? or if you have a boiler run that room on it's own zone.

the 8" vents have to stay, period.

p.s. you say the hot water tanks are 50gal? and only 40K btu's? could you check that again, cause that sounds a little small---thanx

[mechanical'al]

You could convert to high eff. equipment which will directly pipe in its combustion air then you could cover those vents?

[randyl712]

interesting? so this Utility Room is on the exterior of the home? It's not in a basement or Garage?

Sorry if I wasn't clear - the utility room is an unfinished room in a finished basement.

I would get all the pipes (or any pipes) off the cement walls. Use "stand-off" or nail a couple 2x4 to the cement and attach the pipes to the 2x4.

I don't think I can really move anything - the water heaters are all but 1/2" from the cement wall and there's a 1" copper pipe running outside for the landscaping line which hugs the wall tightly. The electrical and gas is attached to the cement wall as well. So I can put up maybe 3/8" rigid foam on this wall but I'd have to cut around a bunch of things. (And I'm not sure the rules about putting it so close to the water heaters)

then I would get some heat in there. sounds like the only way to do that would be electric baseboard heat? or if you have a boiler run that room on it's own zone.
the 8" vents have to stay, period.

I've got direct-vent furnaces in the home so I guess putting an electric heater in there is my only choice? I'm really bummed that I'm basically forced to heat a room with two huge holes to the outside - that just seems whacky to me. And expensive.

p.s. you say the hot water tanks are 50gal? and only 40K btu's? could you check that again, cause that sounds a little small---thanx

Yep, 2 x A.O. Smith GCV-50 Residential Water Heater, Natural Gas, 50 Gallon, ProMax, Tall, 40,000 BTU

You could convert to high eff. equipment which will directly pipe in its combustion air then you could cover those vents?

That's something I've thought of but would cost a few grand to replace 100 gallons of hot water capacity...

[jmac00]

Sorry if I wasn't clear - the utility room is an unfinished room in a finished basement.

how many square feet is the basement? why not pull combustion air from the basement?

Put a 10" holes in the utility room door (use a 12 x 12 return air grill, so it looks nice)

[randyl712]

I've totally thought of that - the basement is large at around 1,500 sq ft and is open to the rest of the house (no doors closing it off) so technically it's much larger still. Looks like 2 x 12x12 vents from the basement to the utility room would supply the air necessary and allow me to close off those exterior intake vents. Any reason NOT to do this? I'm on the fence about which way to go. I just want a comfortable house without insane HVAC bills.

[jmac00]

I've totally thought of that - the basement is large at around 1,500 sq ft and is open to the rest of the house (no doors closing it off) so technically it's much larger still. Looks like 2 x 12x12 vents from the basement to the utility room would supply the air necessary and allow me to close off those exterior intake vents. Any reason NOT to do this? I'm on the fence about which way to go. I just want a comfortable house without insane HVAC bills.

knockyourselfout, I would plug those holes right after I put the 12x12 grills in the door, there is no reason you can't draw combustion air from the basement.

[motoguy128]

2 X 50 gallon water heaters = 1 tankless with room to spare. Probably wouldn't cost much more either and free up a ton of space.

Natural draft and single pipe appliances should be banned in new construction. No need for them anymore except for replacements. Too many issues and potential risk with proper tight home construction.

But for now +1 on combustion air form the basement. It will reduce the point source cold drafts, but remember the actual air requirements and heat lost doesn't change.

[mechanical'al]

ya you can do that though it will induce infiltration as you will be placing the whole structure in a slight negitive the air must come from some where possiblely causing other cold drafts

[darctangent]

I've just bought a house, custom built in 2006, Colorado.

The utility room has two 50-gallon gas hot water heaters in it, the room also houses fire sprinkler system with massive water vessel, well pump pressure tank, water softener, etc.

My issue is that the builder put in two huge combustion air vents to the outdoors, each 8" diameter (one high, one runs close to the floor). I understand that the hot water heaters need combustion air, but these large openings into my house are basically turning the utility room into the outdoors, so when it's freezing outside, it's @#$ cold inside, too. Thus the adjacent rooms in the basement are cold, as are the living spaces above the utility room.

Note that there is no insulation in the room other than on the exterior side, above the concrete slab wall in the space between that and the ceiling joists there's maybe 1-2 feet of fiberglass insulation. I've thought about adding 3/8" rigid foam to the concrete walls where I can (there's electrical boxes, plumbing, gas, etc. touching the concrete so it's not possible to add it uniformly) and I plan on insulating the interior walls with fiberglass insulation to help the adjacent rooms stay warmer.

But - this just doesn't seem right. I'm concerned about letting the room get so darned cold - that can't be good for the water softener, the hot water heaters, etc. It certainly isn't efficient to basically have the water heaters sitting in a room that could be 40 degrees in the winter (or colder?).

I've done some rudimentary calculations - There are 2 x 40,000 BTU water heaters in the utility room, which is 160 square feet, ten foot ceiling height = 1,600 cubic feet.

So my question is - given that this room is becoming a walk-in freezer all winter, how do you keep an outdoor vented space from becoming so cold? Two huge holes into my house is the opposite of efficiency and I'm seriously concerned about the heaters and softeners operating in potentially below-freezing conditions!

Thanks for your help. If you ultimately recommend I have a professional come out, I'd love a specific type of expert who would really know what the heck they're talking about. I feel like I certainly could have a local HVAC guy out to look at it but I would want someone who knows what they're talking about.

I've totally thought of that - the basement is large at around 1,500 sq ft and is open to the rest of the house (no doors closing it off) so technically it's much larger still. Looks like 2 x 12x12 vents from the basement to the utility room would supply the air necessary and allow me to close off those exterior intake vents. Any reason NOT to do this? I'm on the fence about which way to go. I just want a comfortable house without insane HVAC bills.

Where in Colorado? What is your altitude?

You zero in on the water heaters, but you mention nothing about space heating equipment for the home. What heats the home? Where is that system? How many BTU's is that rated at? Does it have combustion air piping as well?

2 X 50 gallon water heaters = 1 tankless with room to spare. Probably wouldn't cost much more either and free up a ton of space.

I disagree. One tankless would rarely give the same preformance when a contractor thought that two 50's were appropriate. Custom homes usually mean more bathrooms than typical and high end tubs/ multi-head showers, etc. On top of that you are almost certainly not accounting for the reduced BTU capacity that goes with most locations in Colorado, a fatal thing to disregard in this state. That being said, niether of us knows without more information.

[randyl712]

Where in Colorado? What is your altitude?

South metro area, under 6,000 ft.

You zero in on the water heaters, but you mention nothing about space heating equipment for the home. What heats the home? Where is that system? How many BTU's is that rated at? Does it have combustion air piping as well?

There are direct-vent gas furnaces in the home also but not in this utility room. They are in other little rooms with direct venting to the outside. They aren't nearby right now but I believe them to be 75,000 BTU units.

I disagree. One tankless would rarely give the same preformance when a contractor thought that two 50's were appropriate. Custom homes usually mean more bathrooms than typical and high end tubs/ multi-head showers, etc.

Spot on - it's a large home, 5 bathrooms, whirlpool tub in the master, two shower valves/showerheads in the master shower as well.


I think we may be inclined to try and insulate the utility room on the interior walls and add a small space heater to keep the room from freezing. It's not ideal but my wife is not sold on the idea of putting holes in the walls for the return registers to open the room to the basement... and the water heaters aren't going to last forever so conceivably we could replace them with direct-vent or tankless down the road and seal up the ducts at that time? Sigh. Wish there was a better solution right now.

[darctangent]

Honestly Randy,

The steps you outlined are more likely to be a treatment for the symtpoms you report, not the actual problem. You need a real professional opinion, not the guesses you will get with the information we have. There are some aspects of the information you have provided that don't line up well with the general design principles that a good contractor would follow, so I think there pieces we are missing. Only an on-site visit from someone properly qualified will be able to deal with your situation. I don't service your area, but I am likely to know of someone who does. If you forward your contact info to me (email address in profile, just click on my name, then the about tab), or alternately post you email adddress in your profile (NOT HERE!!) I will put you in touch with someone. You may also click on the link in my signature line and then fill out a contact form if you wish. Any of the three methods will work.


PS- I have an idea how one might reduce exceess air moving through the combustion air piping, and I will pass that along to my contact.

[Freezeking2000]

I would not seal the openings unless a pro confirms you can.

I would ventilate the room with specially made make up air units that run only when making water. (Fan in a can)

[motoguy128]

I disagree. One tankless would rarely give the same preformance when a contractor thought that two 50's were appropriate. Custom homes usually mean more bathrooms than typical and high end tubs/ multi-head showers, etc. On top of that you are almost certainly not accounting for the reduced BTU capacity that goes with most locations in Colorado, a fatal thing to disregard in this state. That being said, niether of us knows without more information.

It would depend on the BTU capacity of the water heaters. IF they are both 75k BTU units, then I would tend to agree that 1 300k tankless would fall short. However, keep in mind that's it's atill a single family home, and I'm well aware of winter water temps. We hit record lows of 35F incomming water temps here this winter. That still gives you 5gpm at 112F. Plenty to fill a soaking tub and still use a handwash sink. But it might fall short if there was one of those stand-up showers with 20 heads that uses 15gpm. In that case... well in that case, even the 100 gallon storage would run out quick.

A compromise could be to add an electric water heater just as a storage tank and have it just maintain at 120F for hygenic reasons, set the tankless to the same and use a mixing valve to drop it to 115F. IMO there no need to run domestic water over 115F.

[jmac00]

It would depend on the BTU capacity of the water heaters. IF they are both 75k BTU units, then I would tend to agree that 1 300k tankless would fall short. However, keep in mind that's it's atill a single family home, and I'm well aware of winter water temps. We hit record lows of 35F incomming water temps here this winter. That still gives you 5gpm at 112F. Plenty to fill a soaking tub and still use a handwash sink. But it might fall short if there was one of those stand-up showers with 20 heads that uses 15gpm. In that case... well in that case, even the 100 gallon storage would run out quick.

A compromise could be to add an electric water heater just as a storage tank and have it just maintain at 120F for hygenic reasons, set the tankless to the same and use a mixing valve to drop it to 115F. IMO there no need to run domestic water over 115F.

the OP said the tanks are 40K btu (which I think is light for a 50 gal) but read up a few posts and you'll see the BTU rate.

[firecontrol]

An economics point of view. By the time you insulate and add a space heater and the cost year after year to operate the heater you might find that it would be cost effective to change out the 7 year old water heaters with sealed combustion units of some kind.

Some of the aspects are cost vs cost comparisons, but others are comfort and practicability issues. If your home's hot water system has a constant circulator installed that assures hot water at your taps all the time, or even on a timer, you might be able to use a sealed combustion instantaneous water heater with a large electric water heater in line with it. Just a thought.

[RAMHS]

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[beenthere]

RAMHS, this is the Ask Our Pro's forum, and only Pro members that have been vetted by the AOPC may post advise, commentary or ask questions of the OP here.

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Further infractions may result in loss of posting privileges.

[ckartson]

You may consider Installing MOD's ( motor operated dampers) in the combustion air ducts. You would need a pro to do this because the dampers would need to open on any burners call for heat. Both dampers would have to open and provide proof of opening before either burner can fire. This is commonly done in boiler rooms. This may not be possible because many resi hot water tanks don't have provisions for this sequence but some of the direct vent models do. You would need to have someone assess the equipment first.

[darctangent]

dampers are not possible. If you check the OP's post above you will see he has natural draft water heaters. f.y.i the OP appears to have vanished. he appears to be a semi DYI personality.

in my opinion this thread is getting filled with all sorts of extraneous posts that cloud his need for onsite pro. depending on the nature of his issue, the OP may actually have a dangerous condition. He needs a pro.