Heating a duplex

[James Benson]

I have recently purchased a duplex for cheap ($96 000) and it needs a full reno. i just went through the renovation secrets program, and made some changes to my original reno plans. Today i was telling a co worker about what i am going to do and he made a comment about my HVAC (we are both carpenters BTW). he suggested that i remove the forced air system all together since it will create a sound funnel in between units, and will require extra fire and smoke separation measures to be implemented. he then suggested i install a boiler instead and have radiant heat so that the tenants can have separate heating and they can heat rooms individually. this also would allow the main floor to have in floor radiant heat, whereas the basement would have baseboard heaters i think. also i could put a gas fireplace in the living room in each unit to supplement the heat and add to the look and feel of the place (and up the rents too!) any thoughts or suggestions on what kind of heating systems to use and how to best set it all up?

 

[kfort]

Sound separation will never be perfect. Ever. Your target should be the best balance of cost vs acoustic separation.

That said, yeah, hvac ducts are great at transferring everything from a dull whisper and up. Depending on layout, I would probably do hvac & elec baseboard combo. 2x roxul, resilient channel, drywall (possibly x2 If height is ample) & call it a day.

You'll need full fire separation around furnace regardless.

Edit: wait, are these strictly side by side? If so, I would probably go 2 furnaces. And acoustic drywall on at least one side of the common wall.

 

[James Benson]

It is an up and down unit.

Sound separation will never be perfect. Ever. Your target should be the best balance of cost vs acoustic separation.

That said, yeah, hvac ducts are great at transferring everything from a dull whisper and up. Depending on layout, I would probably do hvac & elec baseboard combo. 2x roxul, resilient channel, drywall (possibly x2 If height is ample) & call it a day.

You'll need full fire separation around furnace regardless.

Edit: wait, are these strictly side by side? If so, I would probably go 2 furnaces. And acoustic drywall on at least one side of the common wall.

it is an up and down unit. it is single family home with basement suite that was legalized a long time ago. 7' ceilings so i gotta save space but i can do double insulation and resilient channel and one layer of 5/8 type X drywall. i have to get rid of the old furnace though, its from 1957 and the duct work is just all over the place, its a mess. since i gotta take it all out its no big deal for me to change it, my main question is what is going to be the best system. i can split the electrical because the building has a duplex meter but i cant split the gas. i do care about the environment, so id like it to be environmentally friendly and cost effective. sort of a tall order really.

 

[kfort]

Chances are I would do furnace for up & baseboards for down. Just don't let them run ductwork in stupid places like across the middle of the living / kitchen in the basement.

 

[Matt Crowley]

One of the biggest challenges I've had with up/down suites when it comes to sound attenuation is that you often end up trading ITC's for STC's. (Impact noise vs. ambient room noise). As far as ceilings go I've found that Roxul in joist cavity space and second layer of drywall make a huge difference. Instead of hearing conversations upstairs you hear muffled noise. What it doesn't help with is impact noise like walking, moving furniture around (chairs at dinnertime), kids jumping around, or deep base noises. I haven't found any effective methods to reduce deep base noises actually. I haven't personally installed resilient channels but that is more on the STC side than ITC and I'm not convinced it is worth the investment.

The best bang for your buck, in my opinion, when it comes to sound attenuation in a suite is the flooring you choose to install on the main level. I'm not sure about market demands out east, but out west here carpet in suites is generally a thing of the past. This is unfortunate because carpet is excellent at masking noise and you can put in a nice thick underlayment to muffle noise even further. A lot of tenants like the real clean looking hard finish floors. These are the worst for impact noise. Recently, we installed a LVT (luxury vinyl tile) laminate-looking flooring and I think it is great. It is essentially just a rubber and you can even lift out pieces in the middle and replace them. It is a lot softer than the laminate planks and our tenants believed it was hardwood until we told them what it actually was. I would choose LVT before ceramic in a bathroom as well. Investing in a good underlayment is a great strategy in my opinion.

Basement suites are tougher for turnover and the toughest complaint is to deal with is sound.

As far as heating goes, I would lean towards the two furnaces as well. You end up with two complete / separate sets of ductwork. You have some ceiling height concerns to deal with so it is hard to say without seeing the suite.

 

[kfort]

Resilient is designed to reduce contact area, thereby reducing sound transfer through the material. This would most commonly be impact on the floor of the main suite. Dropping stuff, walking etc.
Edit: and "bass" type noises are significantly harder to muffle. Longer wavelength penetrates objects much easier. Example: subs in your trunk are loud and clear but those tweeter (high pitched) speakers won't be heard. Or, AM radio travelling hundreds of km vs FM travelling dozens...

 

[Owenb]

Have a look at ductless heating systems, or mini splits as they are also known. They are pretty incredible systems and they can be designed for very low temperature. The sound issue will be solved.

 

[Matt Crowley]

Have a look at ductless heating systems, or mini splits as they are also known. They are pretty incredible systems and they can be designed for very low temperature. The sound issue will be solved.

It's almost impossible to "solve" sound transmission. No doubt flanking STC sound will be lessened by a ductless systems.

CMHC article on sound transmission: https://www.cmhc-schl.gc.ca/en/inpr/bude/himu/coedar/upload/Sound-Control-EN.pdf
Alternative source: http://www.woodworks.org/wp-content/uploads/Acoustics_Solutions_Paper.pdf

 

[yaonchung]

My previous home have high velocity heating system. its smaller duck work ideal for limited space installation and heats up the small rather quickly. you can certainly look into it.

 

[RyP]

All great advice here. One thing I would add is to do what you can to have the suites completely separate. If they share an entrance you'll want sound insulated doors to each unit. With separate furnaces, resilient channel and roxul installed, doors were our biggest problem.

Also, if you choose resilient channel it is imperative that it is installed correctly. Meaning that the drywall is only attached to the channel itself and not any wood joists. Even if a couple screws make it into a wood joist the vibration isolation is lost. Many drywalls pay little attention to this detail during install and I believe this is why many believe that it isn't worth the trouble. We've been "lucky" enough to install it both correctly and incorrectly, and the difference was substantial. Albeit, no matter the measures you use sound isolation is only better and never perfect. Good luck!

 

[sbh]

I would check your building code. With baseboard heat via electric or a boiler or even in floor heating, you still need to circulate the air. An HRV system is generally installed and does not take away from head room as you can put them between the joists. Most building codes don't allow you to just pump heat into a unit without air circulation.

Boilers are very efficient and definitely save money on long term utility costs. They can been expensive to install especially if you are running all the water lines. If I was ever doing a full gut renovation I would consider a boiler. I would also consider a boiler if I had very low ceilings and making minimum code for head room was an issue.

Some great points here on sound proofing. One other thing we have found that makes a difference is a solid core door between suites if there is a common stairwell.

 

[Bill Mitsui]

Where are you located? what would be winter temperature like?

For HVAC system,

1. Forced air, most popular system. however, there are costs associated with fire code compliance. costs to install in old brick house. and it might take extra space in basement with low ceiling. Albeit, gas is cheap, much cheaper than electricity and this would not change in next few years. High velocity system would use smaller duck, however, the sound/noise level should be considered.

2. Water system. Boiler system is relatively cheaper to install and you could have a decent zoned heating system (might not be cheap). Some tenants like this type of heating system. I'm not aware there is a bylaw for air cycling, and most fire code would not require air cycling neither. the catch. .. running extra water lines/pipes around home would be a concern if any of them leak. especially in extreme cold eastern area.

3. Baseboard/IR heater, easy to install and change, almost no maintenance, however, in cold area, it is cost forbidden to maintain room temperature at 18 degree in winter.

4. Heat pump, there are few different types of heat source pump, most popular is split heat pump. high installation code. Carrying cost is ok, Fire department would like this type of heating since no much ducts in ceiling/drywall.

You might make a list to compare cost of installing and maintaining.

I have replaced baseboard with superheat p-series mitsubishi slim heat pump (could be used for -20) in Toronto for a multi-family. House is over 100 years old whole brick house.

 

[23994]

Bill,

I am very interested in your past experience of replacing baseboard, can you please share some idea as:

how long will it take?
cost roughly
easy or difficult?
any pre-conditions?

thanks
Sue

 

[Bill Mitsui]

Hi Sue,

It toke 3 days to install 12 split systems for 12 units by contractor who supply all the systems and installations.

The cost varies depends on BTU, between $3000-$6000 per system. Mine was about $4000 per 9000 BTU, per system all included two years ago. I have my own electrician hence the costs of installation were relatively low.

Since we toke out all baseboards and reuse the power line, it was relatively easy to install.

If you could reuse baseboard power supplies that would be a big plus. Heat pumps could be installed on the wall or deck.