Air to water with existing cast iron baseboard?

1915_foursquare

We are in Massachusetts in a 1915 house insulated with cellulose.  We have a Weil McLain 97+ gas boiler running 3 zones (upstairs, downstairs, mud room); the mud room heating is in the floor, the other rooms are cast iron radiators (all but one of which are BaseRay baseboards).  The heat is good but the boiler is becoming increasingly unreliable; we would like better cooling than window AC units can provide;!and we would like to get off gas if possible.

With all that in mind we are getting quotes on mini splits, but I have two concerns.  First, electric rates in New England are high, so we will likely pay more to run mini splits than gas.  Second, radiant heat is much more comfortable than forced air.

I like the idea of air to water heat pumps (although they wouldn’t provide cooling) but it sounds like the operating temperature is much lower than a gas boiler, so it might not be compatible with our radiators.  

Is it even worth getting quotes on air to water systems?  If so what are the important considerations to keep in mind when evaluating proposals?

Hot_water_fan

Start here! https://idronics.caleffi.com/magazine/27-air-water-heat-pump-systems

The short answer is that yes, it works. That doesn’t mean you’ll be 100% off gas, but maybe 90% off gas. 

Air to water can provide cooling actually - however, you are correct that baseboards cannot, so you’ll need ductless heads or ductwork supplied by the air to water unit. 

There aren’t many of these systems out there, so contractors might not have direct experience. Instead, look for the types of contractors that are open to growth and learning. 

GGross

To do this correctly can involve some legwork. Basically what you need to know is the max output temp for your heat pump, the amount of radiation in each room, and the heat loss of each room. Most A2W heat pumps right now are maxing out at 149f output (I think there are some high temp models, but not familiar with them)

- perform a manual J on the whole house, you also need to know the heat loss specifically for each room to make sure there is enough radiation

- is there an A2W heat pump that can output enough BTU/hr to heat the whole house based on the manual J?

- if yes, now you pick your equipment, this should tell you the max temp output the equipment is capable of. Using the radiator manufacturers spec, figure out the output of each radiator based on the max water temp from your A2W.

- If the load of each room is less than the output BTU/h of the radiation in that room at the given water temp, you are basically good to go

I would add that you still probably want a buffer tank, with backup heating elements in case of extreme low temperature. You should not base the system on those backups unless gas is simply not an option, they are not nearly as efficient as the heat pump. Or keep your gas boiler as backup. Personally if the system is already in place for gas I would be more keen on mini splits and keeping the gas boiler for heating. Even if not sized for heating you may be able to make use of them in the shoulder seasons for heating to choose which fuel type will cost you less, many mini splits are pushing COP of 4 or better in mild heating conditions.

Jamie Hall

If you decide to do this, you will have to keep the gas boiler (or go to electric resistance, which you really don't want to do) in good operating condition. This may mean a new boiler whether you go for the air to water heat pumps or not; if the old one is getting creaky, and you will have to decide whether that is a cost you want to incur.

Why? Simply because it is very unlikely that your baseboards can put out enough heat at the maximum temperature that an air to water heat pump can provide to keep you warm. As @Hot_water_fan suggests, it may be as little as 10% of the time, but even that in a typical winter is getting on for 3 weeks. This may not be acceptable to you -- and it will NOT be acceptable to your local building inspector or a hired one, should you decide to sell or try to remortgage the property.

Hot_water_fan

Exactly, the lower water temperatures might prevent an easy drop-in replacement. There are plenty of ways around that in the Caleffi resource. Keeping the boiler as auxiliary heat is probably the cheapest and easiest.

hot_rod

So helpful info here

1915_foursquare

Thanks!  The Caleffi documents were very easy to follow and informative.  Given that the systems are fairly new here I suspect we will just go with mini splits for now.

1915_foursquare

The first mini split quote came in at $27k for 44k BTU.  The equipment (a 5 head Mitsubishi hyper heat system) looks like it would cost maybe $7k retail.  $20k to do the install seems outrageous - is it?  Are installers just pocketing the $10k rebate here?

Hot_water_fan

@1915_foursquare no pricing allowed, sorry. There's a good bit that goes into an installation. I would assume the rebate is split some way between customer and installer.

Is there any way to add ductwork? That'll be higher quality than a ductless system.

1915_foursquare

@Hot_water_fan thanks, I didn’t realize.

Our installation should be straightforward - full, open, unfinished basement, plenty of slots in the 200A panel, etc.  so I don’t know why the quote is so high.

Ducts aren’t really feasible unfortunately.  Maybe the high velocity small diameter ones would fit?

Big Ed_4

New England , Keep the cast iron radiation and stay plugged into the gas line . The mini splits work for those muggy days . As you know they are heat pumps . Use them to heat your home on the days up to before you have to fire up the boiler . Then enjoy the cast iron warmth when you need it . I would not recommend totally relying on heat pumps .

I would also recommend an outdoor reset for your system . It would flatten out the heating cycle . It would give you comfort and fuel savings .

Rule on this board we don't talk pricing ..

1915_foursquare

@Big Ed_4 the mass save rebate of $10k is predicated in having a mini split system that can do all of our heating, AND on us promising not to use the gas system except in an emergency.  I would also prefer not to have to maintain both mini splits and the boiler, and the boiler may need replacing in the next few years if we keep it.  If we size the mini splits for only auxiliary heating, we lose the $10k so we might end up spending more out of pocket for less capability.

We do have a wood stove for backup (and ambiance) which makes the mini splits less of a gamble on terms of heating when it is very cold.

Big Ed_4

It is your call...

pecmsg

1915_foursquare said:

@Big Ed_4 the mass save rebate of $10k is predicated in having a mini split system that can do all of our heating, AND on us promising not to use the gas system except in an emergency.  I would also prefer not to have to maintain both mini splits and the boiler, and the boiler may need replacing in the next few years if we keep it.  If we size the mini splits for only auxiliary heating, we lose the $10k so we might end up spending more out of pocket for less capability.

We do have a wood stove for backup (and ambiance) which makes the mini splits less of a gamble on terms of heating when it is very cold.

No problem then
i promise not to use the gas!

that boiler will be fired up the 1st time the temps hit single digits and the NE Wind begins to blow

Jamie Hall

You have hit the joker in the MassSave rebate system -- either you take the rebate and be honest and freeae, or you take the rebate and lie, or you don't take the rebate. As @Big Ed_4 says, your call.

pecmsg

Jamie Hall said:

You have hit the joker in the MassSave rebate system -- either you take the rebate and be honest and freeae, or you take the rebate and lie, or you don't take the rebate. As @Big Ed_4 says, your call.

At least they’re giving you the option! A lot of areas they won’t even give you that the gas must be removed

Hot_water_fan

If it’s too much hassle, don’t take the rebate. Problem solved! 

Robert_25

1915_foursquare said:

@Big Ed_4 the mass save rebate of $10k is predicated in having a mini split system that can do all of our heating, AND on us promising not to use the gas system except in an emergency.  I would also prefer not to have to maintain both mini splits and the boiler, and the boiler may need replacing in the next few years if we keep it.  If we size the mini splits for only auxiliary heating, we lose the $10k so we might end up spending more out of pocket for less capability.

We do have a wood stove for backup (and ambiance) which makes the mini splits less of a gamble on terms of heating when it is very cold.

You will really miss the radiant heat from the radiators and heated slab if you go with mini-splits. We have a minisplit, and end up turning the boiler on due to cold floors long before the minisplit can't keep up.

Do you plan on using the woodstove to supplement? A woodstove that is properly placed in a home of modest size can help a lot. I have several friends that heat with minispits & woodstoves. The woodstoves are most efficient when the minisplits are the least efficient, so it can work out well with the right setup.

1915_foursquare

@Robert_25 we will likely use the wood stove in the coldest part of the winter.  We have successfully used it to heat the entire house when the boiler was not working, for two separate one-week periods.  The house is a foursquare with a central chimney and a fairly open plan downstairs so the heat circulates well. 

Robert_25

1915_foursquare said:

@Robert_25 we will likely use the wood stove in the coldest part of the winter.  We have successfully used it to heat the entire house when the boiler was not working, for two separate one-week periods.  The house is a foursquare with a central chimney and a fairly open plan downstairs so the heat circulates well. 

That is an ideal setup for a woodstove. Is it a fairly modern woodstove? The new ones burn MUCH cleaner and are more efficient than the models most of us grew up with.

If you really want to get rid of NG but still have some sort of backup central heat, an electric boiler may be worth considering. The electric boiler would be able to run your radiant floor in the mudroom, and also heat the rest of the house if your Minisplits are not up to the task and you were not around to fire the woodstove. The benefit of an electric boiler is that it is basically a hands-off system that is very reliable. The downside is when you DO use it, the cost of operation will be considerably higher than heating with NG.

The best path ford will depend on what your goals are and how much you are willing to spend on the project vs. the ongoing cost to heat your home. You will also need to consider the capacity of your electric service/panel vs. what will be required to replace all of your NG appliances with an electric equivalent.

1915_foursquare

@Robert_25 it is a modern wood stove - Pacific Energy Alderlea T4. And we get excellent draft (two and a half story chimney at the center of a hip roof, with no trees nearby).  We have a wood shed and nearby family with a wood supply, too.

The electric service is 200A with lots of free slots.  We are replacing our (dying, terrible, Samsung) gas range with induction as well.  Hot water is gas fired on-demand; no plans for now to replace that since it is efficient and reliable.  And the dryer is electric.

I would like either keep the gas for backup, if needed, or put in a hydronic heat pump using the existing radiators, if possible.  Ripping out the gas boiler to put in an electric one doesn’t seem to be a great solution for our situation.

Robert_25

1915_foursquare said:

Ripping out the gas boiler to put in an electric one doesn’t seem to be a great solution for our situation.

If you plan on keeping NG service I completely agree.

Big Ed_4

It sucks maintaining a fire in winter ...

1915_foursquare

I am now leaning towards getting air source heat pumps but not taking the whole house rebate, so I can use mini splits for cooling and shoulder season heating but rely mainly on the gas boiler in the winter (supplemented by the wood stove when I feel willing to feed that).  If I go this route I might still size the heat pumps to be able to do the whole house if need be.  Not necessarily the most cost efficient solution but it might not cost that much more than a shoulder-season system to install.  And winters keep getting milder here so long term mini splits might be a better option anyway.