Mod/con boiler flat panel radiators questions

bombaloo

Hello

After much deliberation, I will be replacing my poorly functioning heating and cooling systems at the same time as getting a kitchen addition to my home. Currently have oil steam boiler with cast iron radiators and a high velocity spacepak system for cooling. Home is about 100 years old but has had spray foam put in the walls and closed foam in the attic and double pane windows. A blower door test with thermal imaging was performed and exposed some areas bringing in cold air.   A “short basement” type crawl space will get close cell spray foamed and the house will get some air sealing improvements. Also the home is climate 4A lower Hudson valley NY

The current plan is to remove everything (cast iron boiler, steam pipes, radiators, spacepak air handler, outdoor condenser, duct work. The second floor will get a ducted Mitsubishi hyper heat pump (the bedrooms are small and we really need to reclaim the radiator space for beds and what not). The first floor will get 3 ductless units for cooling and shoulder season heating. There will be a gas conversion and new has boiler for hydronic heating during winter. New pex lines, manifold, etc. The new 400 or so square foot kitchen will have radiant flooring under porcelain tile. This is where I need advice. I am deciding between cast iron radiators or modern flat panel radiators for the remaining first floor to replace all the steam radiators. This decision would also help with the decision to have a cast iron boiler or mod con boiler. I do like the idea of lower temp radiators so I could use a mod con boiler and get greater gas efficiency. Also it would allow me one day to convert to an air to water heat pump when they are more mainstream. If I went with cast iron radiator and cast iron boiler and had my temps at 160-180 i could never reuse it with heat pump. I know cast iron radiators would be easier to be more comfortable and that’s why I’m trying to make my home higher performing with insulation and air sealing to allow lower temp radiators to be a viable option in my old home. 

What would you all do?!

pedmec

I would use cast iron baseboard. its spread out so it covers more outside wall than a flat panel and has thermal mass which helps minimize temperature swings. A little pricey but absolutely great comfort.

Hot_water_fan

This is a false choice. Cast iron radiators also work with lower temps. Likewise, they aren’t any more comfortable than panel radiators, just much heavier . 

You’ll only need the highest temps for the coldest days, so an air to water heat pump would work regardless, but the lower the temp needed of course the more of the hours it will cover.

Jamie Hall

I hope you'll be happy with the results. Taking out the steam is about the last thing i would consider. You are looking at a huge capital expenditure for very little gain in efficiency if any -- and no gain in comfort.....

However... it's your house and your nickel. Or nickels. Given the options you seem to be considering, first I would check the heat load of that kitchen. Assuming there well be some cabinets in there, you probably have a net usable floor area of less than 300 square feet for the radiant, and that works out to a flat out maximum of perhaps 9000 BTUh (7500 BTUh is more realistic). If the heat loss of that space is more than that, you are going to need radiators in there.

As I said above, if you don't mind keeping the cast iron radiators -- keep the steam. Your existing radiators will not put out anywhere hear the heat on hot water than they do on steam, even with non-condensing hot water (at which point you have no efficiency gain over steam). Running condensing temperatures, you will have less than half the heat output from them that you have now with steam. Again, check your heat loss calculations. If that will be adequate... OK. Otherwise, you will need more radiation. You may find your best bet, if you want to run condensing (or in later years, a heat pump) will be a really big array of flat panels.

You do ask what I would do. Keep the steam and get it properly serviced and niost like, piped and venterd the way it should be. Depending on the heat loss in the kitchen, I might use a radiant floor powered by the steam boiler (very simple to do) and, if needed, some additional radiation -- again, steam if possible for minimum size. Then, if I had some cash left over or felt wealthy, I might put in the heat pumps -- if I really needed the air conditioning. You asked...

bombaloo

Jamie Hall said:

I hope you'll be happy with the results. Taking out the steam is about the last thing i would consider. You are looking at a huge capital expenditure for very little gain in efficiency if any -- and no gain in comfort..... However... it's your house and your nickel. Or nickels. Given the options you seem to be considering, first I would check the heat load of that kitchen. Assuming there well be some cabinets in there, you probably have a net usable floor area of less than 300 square feet for the radiant, and that works out to a flat out maximum of perhaps 9000 BTUh (7500 BTUh is more realistic). If the heat loss of that space is more than that, you are going to need radiators in there. As I said above, if you don't mind keeping the cast iron radiators -- keep the steam. Your existing radiators will not put out anywhere hear the heat on hot water than they do on steam, even with non-condensing hot water (at which point you have no efficiency gain over steam). Running condensing temperatures, you will have less than half the heat output from them that you have now with steam. Again, check your heat loss calculations. If that will be adequate... OK. Otherwise, you will need more radiation. You may find your best bet, if you want to run condensing (or in later years, a heat pump) will be a really big array of flat panels. You do ask what I would do. Keep the steam and get it properly serviced and niost like, piped and venterd the way it should be. Depending on the heat loss in the kitchen, I might use a radiant floor powered by the steam boiler (very simple to do) and, if needed, some additional radiation -- again, steam if possible for minimum size. Then, if I had some cash left over or felt wealthy, I might put in the heat pumps -- if I really needed the air conditioning. You asked...

Thank you for these thoughts. Part of me will miss the steam however the only solution to keeping steam would to only keep it on the original first floor house. My bedrooms are very small for modern standards (small in addition to having one corner of each room cut out for the dormer style roof) and freeing up the radiators in them will allow more ideal bed placement, etc. 

In terms of the kitchen yes there is cabinetry plus a 7 x 4 island and some sky lights, windows, sliding patio door so yes I am a bit concerned with the heat loss there and the fact that the radiant surface will be covered. I plan to make those windows highest performing as possible. Triple pane, casement. Wish I could do European tilt n turn but no one here can install those. However, the kitchen will have one of the minisplits so I figure I could use that for additional heating if the radiant floor is not adequate. There is no room for any radiator in the kitchen. If the radiant floor ends up mostly for comfort purposes and I need to use the minisplit to heat it that is ok. I love wood floors and was very hesitant to have tile in the kitchen Becuase of how cold it will feel but heated tile makes it acceptable. 

Mad Dog_2

Depends on your preferred decorating style. With Hot water heater, you have oodles of radiation options:

Standard Baseboard
C.I. Baseboard
Connectors
Runtal Skinny Baseboard 
Panel Radiators 
Free Standing Cast Iron Radiators 
Recessed Sun Rads

Pick a decorating style and go from there. If you oversize radiation, you can use a lower design temperature and harvest the most from a Condensing boiler.

My two cents. Even the Best Cast Iron Baseboard are not the same quality of say 5 yrs ago.  I've installed alot of it. Too many leaks!  Mad Dog 🐕 

Jamie Hall

Well... so be it. For the kitchen radiant floor, you can only use the parts of the floor which are NOT covered by cabinets and that kitchen island. The parts of the floor which are covered must not have radiant tubing under them -- and this needs to be made clear to all and sundry when it is being installed. I very much doubt, frankly, that you have enough usable floor in there to handle the heating requirements of the space -- but I could be wrong. Have been before. If the mini-split in there is a cold temperature capable unit, it may suffice.

Jamie Hall

And furthermore... let me restate: do your heat loss calculations for all the individual rooms very carefully. As I noted before, the heat output from any possible choice of hot water radiation is much less than that of an equivalent sized steam radiator, and if you want to have any efficiency gain at all it will be less than half that of the same radiation running on steam.

bombaloo

Jamie Hall said:

Well... so be it. For the kitchen radiant floor, you can only use the parts of the floor which are NOT covered by cabinets and that kitchen island. The parts of the floor which are covered must not have radiant tubing under them -- and this needs to be made clear to all and sundry when it is being installed. I very much doubt, frankly, that you have enough usable floor in there to handle the heating requirements of the space -- but I could be wrong. Have been before. If the mini-split in there is a cold temperature capable unit, it may suffice.

What is your reasoning for not putting them under the island or exterior wall cabinetry. I’ve done some searching and its topic has come up and many say it’s ok and possibly beneficial for plumbing or getting some heat through the bottom of the cabinetry. Obviously I understand it’s wasted radiation and that it should be avoided under a fridge but what else harm could be done by having it under the cabinetry. 

I could fit in a radiator in the eat in kitchen part of the kitchen but not possible in the L part against the island unless I use a hydronic toe kick blower. Is that something you would recommend?

bombaloo

Mad Dog_2 said:

Depends on your preferred decorating style. With Hot water heater, you have oodles of radiation options:

Standard Baseboard
C.I. Baseboard
Connectors
Runtal Skinny Baseboard 
Panel Radiators 
Free Standing Cast Iron Radiators 
Recessed Sun Rads

Pick a decorating style and go from there. If you oversize radiation, you can use a lower design temperature and harvest the most from a Condensing boiler.

My two cents. Even the Best Cast Iron Baseboard are not the same quality of say 5 yrs ago.  I've installed alot of it. Too many leaks!  Mad Dog 🐕 

I really like the runtal panel radiators look. What is your experience with those in terms of performance, durability.  

Jamie Hall

There are two reasons for not having radiant floor under a cabinet or whatever. The first is -- it's wasted heat. Very little of it will make into the space you are trying to heat up.

It will, however, heat up the cabinet -- and that is the second reason: you will not be able to store any foodstuff in heated cabinet. Most foods go "off" very quickly if they are in a heated or warmed area -- some don't just go "off", they go outright bad. Like make you sick.

hot_rod

If anything a loop under the kitchen cabinet would keep that space warm for plumbing. But really no need or use for tube under cabinet kickspaces.

A kickspace heater is a fin tube with a small blower to push air out into the room. Those are fine under cabinets.

Same applies for couches and beds with dust ruffles that prevent heat from escaping under the bed.

The term we use is heat flux The square footage of the room with the cabinets subtracted out.

So in this 12X12' room, the radiant panel is actually 106 sq ft. That much floor area needs to be able to cover the heat loss of the room.

So if the load for the kitchen was 2880 btu/hr 20 btu/ sq ft.

With only 106 sq feet useable, the load is now 27 btu/ sq ft required. That is getting on the high side for a comfortable radiant floor. Surface temperatures above 82F on design days perhaps?

This is why kitchens may sometimes need additional heat, like a kickspace heater. Especially with 2 or 3 outside walls.

bombaloo

hot_rod said:

If anything a loop under the kitchen cabinet would keep that space warm for plumbing. But really no need or use for tube under cabinet kickspaces. A kickspace heater is a fin tube with a small blower to push air out into the room. Those are fine under cabinets. Same applies for couches and beds with dust ruffles that prevent heat from escaping under the bed. The term we use is heat flux The square footage of the room with the cabinets subtracted out. So in this 12X12' room, the radiant panel is actually 106 sq ft. That much floor area needs to be able to cover the heat loss of the room. So if the load for the kitchen was 2880 btu/hr 20 btu/ sq ft. With only 106 sq feet useable, the load is now 27 btu/ sq ft required. That is getting on the high side for a comfortable radiant floor. Surface temperatures above 82F on design days perhaps? This is why kitchens may sometimes need additional heat, like a kickspace heater. Especially with 2 or 3 outside walls.

Thank you for the advice. This will be for my heating engineer and plumber to work out. This is a plan of the kitchen and I put some red lines to represent the walkable floor of the kitchen. I just randomly put the lines to represent it. Considering this is an addition would you use warmboard-S or just do it manually. 

hot_rod

Looks like a lot of glass on the end of the kitchen, cathedral ceiling and skylights?
Be careful with the loads in that area of the home.

bombaloo

hot_rod said:

Looks like a lot of glass on the end of the kitchen, cathedral ceiling and skylights? Be careful with the loads in that area of the home.

Yes! There will be 3 windows with a built in bench although I think I will make 2 of them picture windows and triple pane. Yes there is a cathedral ceiling so the mini split is going over those windows.  Now that it think of it I could really use a radiator built into the bench like the photo below. 

hot_rod

Skylights too? Typical roof insulation is R-30 x R-50 these days. Putting glass in the roof make it more like R-3. Just be sure to account for these heat loss details.

bombaloo

Jamie Hall said:

There are two reasons for not having radiant floor under a cabinet or whatever. The first is -- it's wasted heat. Very little of it will make into the space you are trying to heat up. It will, however, heat up the cabinet -- and that is the second reason: you will not be able to store any foodstuff in heated cabinet. Most foods go "off" very quickly if they are in a heated or warmed area -- some don't just go "off", they go outright bad. Like make you sick.

I will reconsider keeping steam for my first floor and possibly my oil and cast iron boiler. My question is how many different hot water zones with different temperatures can I have off of a steam boiler. For instance. Can I have one radiant low temperature floor zone for the kitchen and a second zone for an aquacoil 160 degrees going to my attic air handler for backup heat. 

Jamie Hall

bombaloo said:

Jamie Hall said:

There are two reasons for not having radiant floor under a cabinet or whatever. The first is -- it's wasted heat. Very little of it will make into the space you are trying to heat up.

It will, however, heat up the cabinet -- and that is the second reason: you will not be able to store any foodstuff in heated cabinet. Most foods go "off" very quickly if they are in a heated or warmed area -- some don't just go "off", they go outright bad. Like make you sick.

I will reconsider keeping steam for my first floor and possibly my oil and cast iron boiler. My question is how many different hot water zones with different temperatures can I have off of a steam boiler. For instance. Can I have one radiant low temperature floor zone for the kitchen and a second zone for an aquacoil 160 degrees going to my attic air handler for backup heat. 

No problem unless they are huge The attic one will need to go through a heat exchanger, though.